ORIGINAL ARTICLE
Clinical and microscopic evaluation of long-term
(6 months) epilation effects of the ipulse personal
home-use intense pulsed light (IPL) device
M.A. Trelles,1C. Ash,2G. Town3,*
1
Instituto Me´dico Vilafortuny, Cambrils, Spain
2Cyden Institute of Light Therapy, Institute of Life Sciences, Swansea University, UK 3
University of Wales, Global Academy, Swansea Metropolitan University, Swansea, UK *Correspondence: G. Town. E-mail: [email protected]
Abstract
Background The aim of this study is to investigate the cellular mechanism of long-term hair reduction using a novel, square pulse, low-fluence home-use IPL device.
Methods Ten subjects’ axillae (Fitzpatrick III–V) were treated once weekly for four consecutive weeks in a simulated home-use trial. Treated and control site punch biopsies were taken from axillary sites for H&E staining and blinded histological examination before, immediately after and six months after the fourth treatment. The contralateral axilla served as a control.
Results Histologically, four sequential weekly treatments gave a significant increase in telogen compared with anagen follicles. Six months after the fourth treatment, an 87% reduction in terminal hair count (P£ 0.00005) was recorded. An atypical telogen with infundibular dilatation and plugging of keratin and clumping of melanin with disintegration and⁄ or retraction of the intraluminal hair shaft were observed. The papillae remained viable and some new anagen follicles were evident after four treatments. Vellous hairs appeared unaffected by IPL exposures. A mixed inflammatory infiltrate of lymphocytes and eosinophils around vessels of the superficial and deep dermis was sometimes present but the epidermis appeared always normal.
Conclusion A highly significant hair density reduction through induction of telogen followed by miniaturization similar to that achieved in professionally delivered permanent laser hair reduction appears to be the major mechanism of hair reduction using home-use IPL. IPL-induced damage to the isthmus and upper stem may inhibit or interfere with the hair regrowth process. Longer term studies are required to determine if this observed damage is clinically permanent.
Received: 7 July 2012; Accepted: 14 November 2012 Conflicts of Interest
Mario A. Trelles has no conflicts of interest. Godfrey Town receives travel expenses and salary from CyDen Ltd., UK, salary and equity position with GCG Healthcare Ltd., UK, and consultancy fees from UNILEVER, Trumball, USA. Caerwyn Ash is a PhD graduate at University of Wales and received travel grants from the university. He also received salary from CyDen Ltd and has a minor stock holding in the company.
Introduction
The motivation for removal of unwanted body hair can be for a number of cosmetic or medical reasons.1Both men and women have a choice of many methods such as shaving, tweezing, sugar-ing, threadsugar-ing, electrolysis, depilatory lotions and creams, waxing and lasers or intense pulsed light (IPL) to remove unwanted hair.
Photo-selective treatment using lasers and IPL following the principles of selective photothermolysis first proposed by Ander-son and Parrish in 19832has been an increasingly popular method
of hair removal over the past decade since it was first reported in 1996 by Grossman et al.3 Initially, light-based devices used to
remove hair were lasers, with the US Food and Drug Administra-tion (FDA) granting pre-marketing clearance for the use of the q-switched Nd:YAG laser (ThermoLase Softlight; Thermotrex Cor-poration, San Diego, CA, USA) for hair removal using a carbon-based lotion. The principal difference between a laser and an IPL is the range of wavelengths produced by an IPL. However, all have the same mode of action: the selective targeting of the hair shaft melanin to induce a temperature rise leading to destruction or dis-abling of the hair regeneration mechanism with minimal damage to adjacent tissue and epidermis. Although the laser-based approach proved efficacious, high cost and technical complexity
restricted its use primarily to the medical field. The development of the IPL system eventually provided a lower cost, more flexible alternative to the laser, while delivering similar clinical results.4–8
All modern IPL systems use a high-powered xenon flashlamp to generate sufficient optical energy to cause hair depilation. It is these intense flashes of white light being transmitted through the upper layers of skin and absorbed preferentially in the hair shaft and transformed as heat that produce a photothermal response in the pigmented hair shaft, damaging the structure of the hair shaft and conduct heat to adjacent tissue. This process is believed to lead to thermal damage to the pluripotential stem cells surround-ing the hair follicles and results in suppression of further hair growth. Partial discharge (‘square pulse’) IPLs like the one used in this study have the advantage of a constant broadband spectrum output and thus many wavelengths contribute to denaturing the key proteins found in the hair structure, while hair removal lasers only emit a monochromatic light and some lasers may be limited in their suitability for certain skin and hair types.9
The growing demand for simple and effective home-use, hair removal devices has aroused commercial interest among manufac-turers and there is now a proliferation of lasers and IPL systems on the market, some of which are far from accomplishing what is expected from professional photoepilation. Consequently, an objective assessment of light-based home-use systems is needed to check their performance and to validate the effects of hair removal that can only be carried out through controlled clinical studies and the observation of histological effects on the hair structure.
The aim of this ethics committee approved, randomized clinical efficacy and blinded histological study was to investigate the cellu-lar mechanism of long-term hair reduction using a novel, square pulse, low-fluence home-use IPL device and established histopath-ological protocols. The study also evaluates possible significant dif-ferences in the efficacy of the system with the same dose, regardless of Fitzpatrick skin phototype and hair characteristics and additionally, measures hair regrowth over a period of six months after the last of a series of four (one per week) photoepila-tion treatments. Results were compared with those shown by the randomized contralateral axilla, which was shaved once a week over 4 weeks.
Materials and methods
Subjects
Informed consent was obtained from each of the ten subjects par-ticipating in the study. Subjects were enrolled without offering any financial compensation. This contractual arrangement was agreed prior to the commencement of the trial. The treatment sequence and purpose of IPL trials for hair removal were fully explained and all subjects were informed about the three biopsies that would be taken on each axilla: one prior to first treatment, one immediately after the fourth weekly treatment and the third six months after the last IPL treatment. The same biopsy protocol
was performed on the contralateral axilla, which was shaved weekly using a razor and served as a control, at the same time as the other axilla received IPL treatment. Inclusion criteria for the study were as follows: women aged between 18 and 45 years; Fitz-patrick skin phototypes III to V, with dark, thick hair. Subjects were not selected for the study if they had undergone previous epilation using IPL or laser systems. If they had previously used any hair ‘plucking’ method, they must have ceased doing so for at least two months prior to treatment. Exclusions from the study were subjects presenting with any cutaneous disorders and ⁄ or lesions, anomalous skin healing, infection of the treatment area, known photosensitivity, pregnancy, diabetes mellitus, suntan in the area for treatment and subjects using photosensitizing or anti-coagulant medication.
The axilla was chosen as the area for testing because of its acces-sibility for IPL treatment and shaving, ease of assessment and because it is a discreet area that permits taking of biopsies without embarrassment for the subject. Also being bilateral, the axilla per-mits contralateral controlled follow-up of the two methods of epi-lation. Measurements of hair density before treatment were performed in vivo using a graduated magnifying loupe and showed an average of 53 follicles per 6 cm2. Before treatment, a terminal hair count of a selected 6 cm2area was performed for each axilla and recorded in Table 2. The hair-count area was randomly selected and mapped using a template following anatomical refer-ences to facilitate an accurate follow-up of hair regrowth data. Once completed, both axillae of all subjects were shaved using a razor.
IPL device
The iPulse Personal (CyDen Ltd, Swansea, UK) IPL system was chosen as the hair removal treatment device for this study (Fig. 1). The iPulse Personal IPL generates a broadband spectrum of wave-lengths with a 12 mm · 25 mm (3 cm2) treatment area. The device emits a nearly even distribution of energy over 25–60 ms pulse durations, which are within widely recognized thermal
relax-Table 1 Subject demographics
Subject Number Subject characteristics Age Sex Skin type
1 20 F III 2 38 F V 3 18 F IV 4 24 F III 5 32 F V 6 42 F III 7 45 F III 8 37 F V 9 28 F IV 10 35 F IV
ation times (TRT) for successful hair removal (Fig. 2). The device is supplied together with clear ultrasound gel to couple light from the fused silica glass transmission block to the user’s skin. The measured energy ranges from 7 to 10 J ⁄ cm2and is as stated by the manufacturer10(Fig. 3). The device utilizes an electronic capaci-tance sensing safety system composed of four contact pins that measure whether coupling gel is used and if the sensing pins are in positive contact with the skin.
The device treatment parameters were pre-established by the manufacturer, taking into account the varied phototypes and gen-eral hair characteristics of consumers and the need for simplicity of use for self-applied treatments. The treatment programmes offered were determined following independent safety trials for ocular and skin hazard and expected efficacy had already been reported in an independent, published efficacy study simulating home-use.11
IPL treatment
The iPulse Personal IPL parameters employed were identical, regardless of subject’s phototype and skin characteristics. The pro-gramme selected was ‘Fair’ (10 J ⁄ cm2, single pulses of 25 ms dura-tion), with two passes. ‘Simulated home-use’ treatment was applied by a qualified operator in individual 3 cm2spots through
a layer of transparent light-coupling gel at room temperature. The handpiece was moved after each pulse to an adjacent area leaving a space in between to avoid overlapping of light energy and possi-ble skin burns due to build up of thermal gradient, using the cou-pling gel as a visual indicator of the treatment pattern. When the entire area was covered, a second pass was carried out, but this time light pulses were delivered centring the 3 cm2window of the handpiece on the non-treated spaces, once again leaving a space between them, until the entire area of axilla hair was treated. In this way, if any treatment areas were inadvertently overlapped, the time delay between the two passes reduced the possibility of any heat accumulation. The total number of pulses per axilla varied from 10 to 16 (average 13 pulses) with a delay time between pulses of 6 s. All subjects were treated once weekly for four consecutive weeks.
Prior to commencement of treatment, a test pulse was made on the darkest parts of the skin of each axilla. After 10 min, observa-tions were made to ascertain whether there was any adverse reac-tion such as significant erythema, skin burning or blister formation. The full treatment was then carried out following the sequence described above.
The IPL application was performed, ensuring full contact with the skin through the transparent gel layer and the 3 cm2handpiece window on the skin surface. The light-coupling clear ultrasound gel was at room temperature and was applied in an approximately 3 mm thick layer. At the time of treatment, the quartz-glass win-dow of the IPL hand piece was applied to the skin maintaining good contact when the lamp was fired. Although this was a simu-lated home-treatment study, immediately post-treatment, an anti-inflammatory prednicarbate ointment normally used only in a clinical setting (Peitel Cream, Laboratorios Novag, S.A. Barcelona, Spain) was routinely applied to the IPL-treated and control areas. It is acknowledged that this topical steroid ((11b)-17-[(ethoxycar-bonyl)oxy]-11-hydroxy-3,20-dioxopregna-1,4-dien-21-yl propio-nate), will have suppressed signs of inflammation in the same way as Aloe Vera. In any event, the application of this topical steroid will have had no known impact on the epilation effects of IPL
Table 2 Hair regrowth after IPL home-use device depilation. Average hair count before treatment was 53.4 in the 6 cm2area (average 8–9 hairs per cm2)
Subject number Area of 2· 3 cm with an average hair count per 6 cm2 Before treatment Before 4th treatment 2 weeks after 4th treatment 6 months after 4th treatment 1 48 25 2 2 2 36 12 1 6 3 54 16 2 0 4 42 15 2 3 S 36 48 16 28 6 60 5 2 3 7 78 11 9 10 a 54 2 0 3 9 72 8 7 8 10 54 10 1 8 Average hair count per 6 cm2 53.4 15.2 4.2 7.2 Averagrt hair reduction 72% 92% 87%
Figure 1 iPulse Personal home-use intense pulsed light used in this investigation.
treatment. Each subject was instructed not to use any method of epilation on the treated area, until the following treatment session and to note down the day on which they first noticed hair regrowth. Aloe Vera (Profarplan Laboratory, Barcelona, Spain) was provided to all study subjects and recommended for use at home on the treated axilla three times a day for 3 days, which was sufficient to alleviate any discomfort and make cutaneous signs disappear.
Subject assessment
An inter-subject hair density visual scale scoring from 0 to 100% was presented to each subject prior to treatments, starting imme-diately before the second treatment. The subjects were informed that hair density should be considered a maximum of 100% before starting the block of four treatment sessions. Consequently, they were to score results achieved based on the density of hair observed at each time point, which was expected to be progres-sively less. The score was to be recorded as zero if hair was com-pletely eliminated and no regrowth was noticed at six months after the fourth treatment. Subjects were informed that all results
regarding hair regrowth would determine the satisfaction index with the treatment. If hair regrowth was of high density this would mean Dissatisfied (DS) and so, medium density would be Fair (F), regrowth of little density would be Satisfied (S) and no regrowth would be Very Satisfied (VS).
Photographic assessment
Also, terminal hair counts and high-resolution digital photogra-phy were performed prior to the fourth treatment (week 4), two weeks after the fourth treatment and 6 months after the fourth treatment and compared with the hair count prior to treatment. For this examination the same 6 cm2 area was checked. To ensure accuracy regarding location of the area for the hair count, each subject’s axilla was mapped using a template. Five parame-ters were analysed: (i) reduction in the number of terminal hairs, (ii) the time that the area was free of hair, (iii) any side-effects, (iv) subject satisfaction and (v) histological follow-up. After the weekly check-up, on the same day that the IPL treatment was carried out, the therapist shaved the contralateral axilla with a razor.
Figure 2 Graph shows the relationship of target diameter and the TRT. The shaded area indicates calculated TRT of a typical terminal hair follicle of 200 lm diameter.
Figure 3 Pulse durations and Fluence values for treatment settings of the iPulse Personal.
Statistical analysis was performed using Microsoft Excel Ana-lyse-It software (IBM, New York, NY, USA). The degree of hair density reduction was analysed using the Wilcoxon Signed Rank Test.
Histological assessment
Skin histology samples were taken under local infiltration anaes-thesia with Mepivacaine without vasoconstrictor (Scandinabsa, Laboratorios Inibsa, Barcelona, Spain) before treatment, 15–20 min after the fourth treatment and at 6 months. An incisional oval-shaped 8 mm diameter biopsy was taken in the direction of hair growth, making sure that it included the deep dermis. A total of three biopsies of each axilla from each subject were obtained during the study. Biopsies were taken ensuring that they corre-sponded to different areas of the axilla for each subject. Samples were formalin-fixed, paraffin-embedded, sectioned either in the transverse direction (perpendicular to the long axis of the folli-cle) or in the longitudinal direction, (parallel to the long axis of the hair follicle) and stained with Hematoxylin and Eosin (H&E) for optical microscopic evaluation. An experienced inde-pendent pathologist who was familiar with the photoepilation technique performed a blinded microscopic evaluation.
Results
Subjects
Subjects’ demographics are shown in Table 1. None withdrew from the study.
Adverse events
During treatment, no subject experienced sufficient discomfort to abandon treatment and subjects reported only bearable heat or a stinging sensation. They also commented that a slight pain like a rubber band ‘flicking’ the skin was felt during treatment.
When treatment sessions ended, perifolicular oedema was noticed together with reactive erythema. The latter progressively increased as reported by subjects and started to decrease between 6 to 12 h later. Subjects with dark phototype skin experienced more evidently these two treatment-related effects. All 10 subjects expe-rienced slight burning sensation and itching but those who appar-ently experienced the most discomfort were the darker Fitzpatrick Skin Type V phototype skins.
No burns or changes in skin colour were observed at any time point when subjects came for treatment.
At the weekly check-ups, no late-emerging epidermal side-effects were seen in any skin phenotype and epidermal melanin distribution appeared normal.
Hair counts
Hair counts were performed prior to fourth treatment, 2 weeks after fourth treatment and 6 months after the series of four IPL epilations were carried out, and are presented in Table 2. Hair
elimination progressively became more evident and prior to the fourth treatment there was practically no hair with the exception of subject number 5 who presented with an apparent total regrowth of hair. However, in this case the hair at the 6-month assessment was finer and lighter in colour. At the time of hair counts in the selected areas, an average reduction of over 70% was shown.
Hair counts taken before commencement of the treatment regime showed an average of 53.4 hairs in the 6 cm2 region of investigation. After three treatments, immediately before the fourth, the average hair count in the same region was 15.2, a reduction of 72%. Two weeks after the fourth treatment, the hair count was reduced to 4.2 hairs, a reduction of 92% overall. Six months after the fourth treatment, the average hair count in the region was 7.1 reflecting a reduction of 87% in terminal hair count (P £ 0.001) using the Wilcoxon Signed Rank Test. Reduction of the number of hairs in the area selected for observation always varied by three to four hairs in the 6 cm2area of examination. Subject assessment
The satisfaction index, in relation to results achieved, is presented in Table 3. Subjects’ opinion regarding hair growth and density were translated into scores: DS, F, S and VS according to reduc-tion in hair populareduc-tion, comparing what they presented with before and six months after treatment.
Once the series of four treatments were completed, at the 6-month assessment, subjects reported that in the axilla treated with the IPL home-use device, hair had started to regrow from the third month onwards but hair density was less in all cases com-pared with pre-treatment. Contralateral axillae, which were not treated, appeared with normal rates of hair regrowth in all sub-jects and showed notable differences compared with the treated axilla. Also, subjects remarked that the skin of the IPL-treated axilla presented a better, healthier aspect and it was smoother to touch.
Table 3 Subject satisfaction index and hair counts. Area exam-ined 2 cm· 3 cm (6 cm2 ) Subject number Subject satisfaction at 6 months
Observations regarding hair regrowth
1 S Regrowth was of a few hairs 2 VS Practically no regrowth 3 VS Absence of hair regrowth 4 S Limited hair regrowth
5 DS Hair regrowth but was finer and less 6 S Minimal hair regrowth
7 F Regrowth was noticeable but less 8 S Regrowth was of very few hairs 9 F Regrowth was noticeable but less 10 S Regrowth of very few hairs DS = Dissatisfied; F = Fair; S = Satisfied; VS = Very Satisfied.
Histological results
Prior to treatment, skin presented in a normal pattern with abun-dant hair follicles of normal aspect. The epidermis was normal, multicellular and undulating with intermittent regular protrusions of the epidermis layer (rete pegs) into the upper layers of the under-lying dermis. The dermis looked normal with well-distributed fibres and appendages. This characteristic was maintained in all biopsies taken from the control contralateral axilla at all points of biopsy assessments.
Four sequential weekly treatments produced follicles with clear treatment effects, which consisted of an increase in telogen com-pared with anagen follicles as well as the presence of some minia-turized hairs. Moreover, effective retarded hair regrowth was noted and was more effective and prolonged in the regrowth ratio, when compared with the contralateral axilla shaved with a razor blade.
In biopsies taken from treated skin at 15–20 min post-treatment, marked changes were present in the lower part of some hair follicles (Fig. 4). The matrix area remained viable in the majority of follicles, however, in a few of them, they were reduced in size and had a darker colour (Fig. 5). An atypical telogen was seen and the base of the hair fibre was retracted upwards. The affected hair follicles showed infundibular dilatation with plugging of keratin and clump-ing of melanin with disintegration and ⁄ or retraction of the intralu-minal hair shaft (Fig. 6). A denaturation of collagen near the follicles and a mixed inflammatory infiltrate of lymphocytes and eosinophils around vessels of the superficial and deep dermis were present. Morphological changes in the hair shaft were noticed that could be related to thermal light effect. The epidermis and the appendages appeared normal and unaffected. Some new anagen follicles were evident after four treatments.
Histological changes noted in the standard hair architecture fol-lowing the IPL treatment fulfil efficacy parameters of treatment to obtain extended hair regrowth delay under safe circumstances. The follicles showed typical telogen morphology, with infundibu-lar dilatation, plugging and marked proliferation of the stem outer sheath. Clumping of melanin and mild trauma of the intraluminal hair shaft was observed. The papillae always remained viable and some new anagen follicles were evident after four treatments, but there were no hairs extending to or through the epidermis. Vellous hairs appeared unaffected by IPL exposures due to small follicular diameters and a much lower concentration of melanin. A mixed inflammatory infiltrate of histiocytes, lymphocytes and eosinophils around vessels of the superficial and deep dermis as well as some hialinization of the collagen were observed.
Discussion
Despite many practical technology advances in light-based epila-tion, little remains known about the molecular mechanisms driv-ing cell differentiation in the hair follicle or precisely why thermal damage to the follicular matrix and adjacent tissue results in pro-longed hair regeneration delay and follicular involution. It is
gen-Figure 5 Tangential section after treatment, stained with hema-toxylin and eosin, magnification· 10, showing miniaturization of some hair follicles.
Figure 4 Hair follicle biopsy taken 15–20 min after treatment, stained with hematoxylin and eosin, magnification· 10, showing disintegration with retraction of the intraluminal hair shaft and plugging of keratin (longitudinal section). Epidermis presents with no damage and slight coagulation is seen in the upper part of the hair structure.
erally accepted that progenitor cells in the matrix generate individ-ual follicles during each growth phase and that stem cells, believed to be located in the follicular bulge in the upper third of the folli-cle, contribute to rebuilding cycling hair follicles.12,13A review of the literature shows that many of the published histological studies are more than 10-years old and subsequent claims by manufactur-ers and clinicians rely on this early work with short-pulsing nor-mal mode ruby lasers for hair removal and the current route to FDA 510(k) pre-marketing clearance in the United States still fol-lows histological evidence provided by researchers at that time.
In 1996 in a pilot histological study, Grossman et al. assessed damage to hair follicles in ex vivo black-haired dog skin to design a human study.3 Using a 270 ls short-pulsing, normal
mode ruby laser at 694 nm at radiant exposures from 40 to 160 J ⁄ cm2, and it was shown that damage ranged from focal
damage to the follicular epithelium and alteration of the periad-ventitial collagen with focal damage in the reticular dermis immediately adjacent to the hair follicle at 40 J ⁄ cm2, to conflu-ent damage to dermal structures, reticular dermis and adnexae at 160 J ⁄ cm2. In the corresponding human study, in all cases little or no apparent histological difference was noted at fluences of 30–60 J ⁄ cm2, hair shafts showed fragmentation and eosinophilia and there was heterogeneous but widespread injury to follicular epithelium seen as cytoplasmic eosinophilia and nuclear conden-sation. There was only one case (at the highest fluence) of focal thermal coagulation of perifollicular collagen in the dermis. Although the data in this study suggested a low damage thresh-old for induction of growth delay and a higher damage threshthresh-old for permanent hair loss, it was acknowledged by the authors that the pulse duration of 270 ls was well below the estimated TRT for both follicles and epidermis and that the relative importance of thermal denaturation vs. vaporization and mechanical damage remained uncertain.
As early as 1997, Dierickx et al. observed, following a 2-year his-tological hair removal study using a 270 ls ruby laser, that while the biological mechanisms by which ruby laser pulses cause per-manent loss of terminal hair remain unknown, the study strongly suggested that miniaturization of coarse terminal hair follicles to vellus-like hair follicles was involved, producing non-scarring alo-pecia and that the histological picture of miniaturized follicles after laser treatment corresponded to the histological picture of andro-genic alopecia. Thus, the gradual transformation of terminal to shorter, finer, less pigmented, vellus-like follicles is a major feature of light-based permanent hair reduction.14
Similar histological results using 10–40 J ⁄ cm2 and 1 ms and 3 ms pulse duration normal mode ruby lasers were reported in 1999 by Omi et al. and McCoy et al. respectively.15,16McCoy
con-cluded that while there was no evidence of permanent follicle death after one ruby laser treatment and despite evidence of persis-tence of follicular elements after two and three treatments, it is possible that laser-induced damage to the isthmus and upper stem may interfere with the interaction between dermal and epidermal germinative cells, thus inhibiting or altering the normal hair cycle. In a further investigation in 2002, McCoy et al. concluded after studying biopsies at up to 6 months that induction of telogen in terminal follicles followed by miniaturization appears to be the main mechanism of ruby laser hair reduction.17
In 1999 in a study employing light microscopy and scanning electron microscopy, Lieuw et al. reported that although damage to the follicular cells is mainly thought to be thermal in nature, it is probably compounded by the presence of an inflammatory response, as seen in the histological sections presented in their study. It was also proposed that failure to destroy the hair bulb may explain the regrowth of hair after ruby laser irradiation.18
Currently, no consensus exists on a definition for treatment-induced ‘permanent’ hair loss despite frequent use of the term to describe the effects of electrolysis and light-based hair removal. Clinical providers of light-based hair removal treatments and the FDA have both generally adopted the specific definition provided by Dierickx et al. in 1997 that ‘permanent’ hair loss is a significant reduction in the number of terminal hairs after a given treatment that is stable for a period longer than the complete growth cycle of hair follicles at the given body site.14According to the FDA, ‘Per-manent hair reduction is defined as the long-term, stable reduction in the number of hairs re-growing after a treatment regime, which may include several sessions. The number of hairs re-growing must be stable over time greater than the duration of the complete growth cycle of hair follicles, which varies from four to twelve months accord-ing to body location. Permanent hair reduction does not necessarily imply the elimination of all hairs in the treatment area’.19
From the results of these early studies, it is therefore not sur-prising that initial hair reduction success with high-energy short-pulsing q-switched lasers operating in the nanosecond domain was short-lived and the Normal Mode Ruby Laser results using pulse durations between 270 ls and 3 ms provided the first
defini-Figure 6 Hair follicle section after treatment, stained with hema-toxylin and eosin, showing infundibular dilatation and plugging of keratin with mild trauma of the intraluminal hair shaft. Notice dis-ruption (separation) of the trichilemmal keratinization and a few inflammatory cells in the dermis.
tive evidence of permanent hair reduction. During the last two decades, IPL devices have appeared in the market, initially mim-icking the pulse durations of the early ruby and alexandrite lasers and subsequently developing extended pulse durations and trains of sub-pulses more closely aligned to the accepted optimal pulse duration of 20–100 ms to match the TRT of the average range of hair follicles. The most recent development of ‘square pulse’ IPL technology further advances potential efficacy of hair reduction by delivering a constant spectral ‘footprint’ of biologically effective duration and wavelengths at radiant exposures comfortably below the threshold for epidermal damage but above recognized lower limits for effective hair reduction.20
To achieve effective epilation, it is accepted that destruction of the cells of the follicular matrix producing irreversible lesions to the ‘bulge’ area is necessary. Currently, there is speculation as to the importance of the papilla as a possible significant target for effective photoepilation treatment.
The IPL system used in this study offers three pre-set programmes, to epilate individuals of Fitzpatrick skin phototype I to IV effectively. According to our clinical observations, with two passes, no adverse reactions were produced, even in dark photo-types, using the programme for ‘Fair’ skin, which is the highest energy setting. Although treatment uses relatively moderate fluence compared with some professional systems, energy is released evenly throughout the duration of the pulse to avoid any ‘peak’ thermal build-up. If, however, multiple high-energy pulses are repeatedly ‘stacked’ by incorrectly discharging the IPL on the same spot, the skin may suffer an adverse reaction. If this situation arises, particu-larly because of superimposition of pulses, we have observed in trials conducted at the preparatory stage of this study, that skin suffers a first-degree burn, especially in dark phototypes, which peels in about a week without leaving traces of any pigmentary com-plication. Repetition rate between pulses is fixed at 6 s. The delay time permits heat dissipation and tissue cooling, so that uncon-trolled thermal build-up and risk of skin burning are avoided.
The primary chromophore that absorbs photons emitted by the IPL is the melanin within the hair follicle, the structures next to the dermal papilla and the cells of the ‘bulge’. To achieve this objective, sufficient prolongation of heating of the chromophores must take place to allow thermal transfer from the primary target to adjacent vital hair structures and accomplish damage to follicu-lar stem cells.
Once the main melanin target of the hair follicle (approximately 200–300 lm diameter) is thermally saturated, heat effects advance outwards to the entire involved structures of the hair follicle, which are implicated in hair vitality. The application of longer pulses than the TRT of the hair shaft allows propagation of a ther-mal volume with a damaging effect, which causes changes in the viability of follicular stem cells. This is important to achieve long-term epilation.
IPL systems are categorized into two types, free discharge and square pulse. A free discharge system delivers peaks of
uncon-trolled high-power optical energy, within a fixed pulse duration and as a consequence, it is not possible for the operator to select an optimal pulse duration of ‘useful’ light to match the true TRT of the biological target. Since the effective pulse duration is vastly shorter than the overall pulse duration, this may result in excessive energy accumulation by skin chromophores leading to adverse skin reactions such as severe erythema or blistering of the subject’s skin and subsequent transient hyperpigmentation.
A constant delivery of optical energy across the pulse duration within the time period of the TRT ensures a constant spectrum of ‘useful’ optical energy to the intended target chromophores and reduces the risk of exceeding the threshold of damage to skin structures by allowing a lower total power delivery than the free discharge method. Significantly, lower energies can be used to obtain equivalent clinical results compared with free discharge sys-tems with variable spectral output and high fluences or grouped short peaks of light energy.21
In the case of the IPL used for this study, fluence and pulse time are relatively constrained owing to the target market of consumers who will use the device. The fact that emitted wavelengths and energy are constant throughout the pulse facilitates effective epila-tion.
The potential criticism of not having enough energy for com-plete hair bulb elimination as compared to many high-power pro-fessional medical IPL and laser devices holds two lessons: a greater margin of safe use of the personal device by a member of the gen-eral public and less evident efficacy after only four treatments. However, it is expected that depilation conducted frequently at home by the user will lead to comparable permanent results of hair elimination over extended periods of time provided that treat-ments are carried out on a regular basis.
Conclusions
Using the treatment regimen described in this study, the device produced a highly significant reduction in hair density.
The histological outcomes in this home-use IPL study are con-sistent with the recognized findings of earlier researchers into the microscopic changes seen in professional systems for laser-assisted permanent hair reduction.
Induction of telogen followed by miniaturization similar to that achieved in professionally delivered laser hair reduction appears to be the major mechanism of terminal hair reduction using home-use IPL. IPL-induced damage to the isthmus and upper stem may inhibit or interfere with the hair regrowth process. Longer term studies are required to determine if this observed damage is clini-cally permanent.
Acknowledgements
This study was contracted to the Antoni de Gimbernat Foun-dation and was conducted at the headquarters of the Instituto Me´dico Vilafortuny, Cambrils, Spain.
The report given in this study is registered in the academic activities of the FUNDACION ANTONI DE GIMBERNAT year 2009–2010.
The authors thank Dra. Adriana Ribe´ Ph.D., Ribe´ Clinic, Paseo de Gracia, 91, 3–2 Barcelona, Spain an independent pathologist who processed the punch biopsies, prepared and stained the histology sections, and performed a blinded evalua-tion of the selected biopsies using light microscopy.
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