Permanent Hair Removal by Normal-Mode
Ruby Laser
Christine C. Dierickx, MD; Melanie C. Grossman, MD; William A. Farinelli; R. Rox Anderson, MD
Objective:To assess the permanence of hair removal by normal-mode ruby laser treatment.
Methods:Hair removal was measured for 2 years after a single treatment with normal-mode ruby laser pulses (694 nm, 270 microseconds, 6-mm beam diameter). Observations:Six test areas on the thighs or backs of 13 volunteers were exposed to normal-mode ruby laser pulses at fluences of 30 to 60 J/cm2delivered to both
shaved and wax-epilated skin. In addition, there was a shaved and wax-epilated control site. Terminal hairs were manually counted before and after laser exposure. Tran-sient alopecia occurred in all 13 participants after laser exposure, consistent with induction of telogen. Two years
after laser exposure, 4 participants still had obvious, sig-nificant hair loss at all laser-treated sites compared with the unexposed shaved and wax-epilated control sites. In all 4 participants, there was no significant change in hair counts 6 months, 1 year, and 2 years after laser expo-sure. Laser-induced alopecia correlated histologically with miniaturized, velluslike hair follicles. No scarring and no permanent pigmentary changes were observed. Conclusions:Permanent, nonscarring alopecia can be induced by a single treatment with high-fluence ruby la-ser pulses. Miniaturization of the terminal hair follicles seems to account for this response.
Arch Dermatol. 1998;134:837-842
U
NWANTED HAIR is ama-jor cosmetic and surgi-cal problem. Many tem-porary hair removal methods exist, includ-ing shavinclud-ing, wax epilation, and use of chemical depilatories.1,2Electrolysis is a
well-established method for permanent de-struction of terminal hair follicles. How-ever, the method is tedious, and efficacy has been reported to range from 15% to 50% permanent hair loss.3Scarring can
oc-cur after electrolysis, especially if inex-pertly performed.4
Damage to hair follicles based on the theory of selective photothermolysis5has
been reported recently.6Thirteen
volun-teers with brown or black hair were ex-posed to normal-mode ruby laser pulses (694 nm, 270 microseconds, 6-mm beam diameter) at fluences of 30 to 60 J/cm2
de-livered to both shaved and wax-epilated skin sites on the thighs or back. In all 13 participants, laser exposures produced a
hair growth delay consistent with induc-tion of telogen. Ruby lasers have been com-mercialized for hair removal, but the ques-tion remains whether permanent hair loss can be induced by selective photother-molysis. Four study participants6had
clini-cally obvious hair loss at the final fol-low-up visit 6 months after exposure, each of these with less than 50% regrowth of terminal hairs. We decided to follow up the participants of this first study at 1 and 2 years after laser exposure to evaluate the permanence of hair removal.
RESULTS HAIR LOSS
Results at 6 months’ follow-up have been published previously6 but did not
ad-dress the question of permanent hair loss. Of the 13 participants, 7 were fol-lowed up for 2 years after laser exposure.
For editorial comment
see page 867
This article is also available on our Web site: www.ama-assn.org/derm. OBSERVATION
At 1 year and 2 years after laser treatment, 4 of these 7 participants still had obvious hair loss confined to laser-treated sites and 3 had complete or nearly complete hair regrowth. In all 7 participants, there was no significant change in terminal hair counts 6 months, 1 year, and 2 years after laser exposure.
Figure 1, left, illustrates hair loss on a partici-pant’s back 1 year after laser exposure. The hair loss is fluence dependent, with the greatest loss at the highest fluence (60 J/cm2). Figure 1, right, illustrates the same
sites 2 years after treatment. The same amount of hair loss is still present.Figure 2, top and bottom, show the same site on an upper thigh treated with 60 J/cm2
at 3 months and 2 years, respectively. No substantial change in the clinical appearance of the alopecia is seen. Neither pigment changes nor scarring was seen in any participant at the 12- and 24-month follow-up visits.
Hair loss at 6, 12, and 24 months after a single laser exposure in the 4 participants showing perma-nent hair loss are plotted vs fluence inFigure 3. Sites treated with 60 J/cm2(highest fluence) after shaving
had the greatest hair loss, 64.3% ± 1.1%. Statistically significant hair loss was seen at 6 months for all flu-ences at both shaved and epilated sites compared with the unexposed shaved and epilated control sites. At 1 year and 2 years, there was significantly less hair only
in the shaved sites for all fluences compared with the untreated control site.
HISTOLOGICAL FINDINGS
Terminal and velluslike (miniaturized) hairs were iden-tified on the transverse sections and counted by estab-lished criteria.8-10 Terminal-velluslike hair ratios were
calculated from the follicular counts, and fibrous tracts were recorded as absent or present. Results are shown in theTable. The total number of hairs was identical in the control and laser-treated sites. However, in the laser-treated sites, there was a reduction in large termi-nal hairs with a reciprocal increase in small velluslike hairs. The average hair shaft diameter measured from the histological sections also decreased after laser treat-ment (Figure 4). There were no signs of fibrous tracts, and normal-appearing sebaceous glands were still pre-sent around the miniaturized hair follicles.
COMMENT
The results of this study show that permanent loss of terminal (coarse) hair can result from a single treat-ment with high-fluence, normal-mode ruby laser pulses. The lack of change in any participant’s termi-nal hair counts beyond 6 months after laser exposure
PARTICIPANTS AND METHODS
Thirteen adult volunteers (12 men and 1 woman) con-sented to participate, as previously described.6All had fair skin (Fitzpatrick type I, II, or III) and brown or black hair. Test sites were chosen on the back or poste-rior aspect of the thighs based on uniformity and density of terminal hairs. Eight 33 2-cm areas were mapped and photographed. Baseline hair counts were obtained from each site by manually counting and marking terminal hairs. Before laser exposure, half of the test sites were shaved and half were epilated with cold wax (My-Epil, Laboratoire Suzy, Montreuil, France). Sites were irradi-ated with a normal-mode ruby laser, described below, at fluences of 0 (unexposed control), 30, 40, and 60 J/cm2. Laser pulses were given in a contiguous, nominally nonoverlapping pattern that covered the entire test site.
Clinical evaluation, terminal hair counts, and pho-tographs were obtained 1, 3, 6, 12, and 24 months after laser exposure. One participant who had obvious alope-cia in all laser exposure sites at all of these follow-up vis-its consented to biopsy examination. Three-millimeter punch biopsy samples were obtained before treatment and at 1 year after laser exposure from a site with alope-cia treated at 60 J/cm2after shaving. Tissue specimens were processed for light microscopy of horizontal sec-tions with a technique using trisection or quadrisection that maintains all sections in the same anatomic orienta-tion (deep to superficial) on the microscope slides.7All specimens were stained with hematoxylin-eosin for light microscopy.
DATA ANALYSIS
Hair loss was defined as the percentage of terminal hairs absent after treatment compared with the number before treatment. For each site, at each follow-up visit, hair loss was calculated. Results for each experimental condition were pooled for all participants. The mean ± SD for each condition was calculated. A paired t test was used to determine significant differences (P,.05) between post-treatment and prepost-treatment hair counts for each experi-mental condition at the 6-, 12-, and 24-month observa-tion times.
LASER AND DELIVERY APPARATUS
suggests that 6 months’ follow-up may be sufficient to assess final outcome after treatment for hair removal.
The mechanisms by which high-fluence, normal-mode ruby laser pulses induce selective damage to hair follicles6are based on the principles of selective
photothermolysis.5At 694 nm, light penetrates well
into and through the dermis, and follicular melanin is
by far the dominant chromophore in the dermis.11
Laser pulse width also seems to play an important role, as suggested by the thermal transfer theory.5
Thermal conduction during the laser pulse heats a region around each microscopic site of optical energy absorption. The spatial scale of thermal confinement and resulting thermal or thermomechanical damage is therefore strongly related to laser pulse width. Q-switched (nanosecond domain) laser pulses effec-tively damage individual pigmented cells within hair follicles by confinement of heat at the spatial level of melanosomes,12leading in animals to leukotrichia but
not to hair loss after Q-switched ruby laser pulses.13
Consistent with this behavior, permanent hair loss has not been reported in humans after Q-switched laser treatment despite a decade of widely using Q-switched ruby and Nd:YAG lasers for tattoo removal. The ther-mal relaxation time of whole hair follicles is between 1 and 100 milliseconds, depending on size. Thermal relaxation of human terminal hair follicles has never been measured but is estimated to be about 10 to 50 milliseconds.6,14,15
The 0.27-millisecond ruby laser pulses used in this study were clearly long enough to cause thermal coagu-lation and vaporization injury of hair follicles,6leading
to a growth delay6in all participants and permanent
hair loss in some. However, in theory, the longer-pulse (3-millisecond) ruby laser now commercially available for hair removal may be more ideal for several reasons. First, it is still unknown which “targets” in hair follicles are responsible for permanent hair loss. A somewhat
Figure 1.Left, Test sites on the back 1 year after ruby laser treatment. Site 1 was treated with 30 J/cm2, site 2 was treated with 40 J/cm2, and site 3 was treated
with 60 J/cm2. Site 4 was left untreated and served as a control. A fluence-dependent regrowth is apparent. Right, Two years after a single laser treatment, the
longer pulse width should allow more thermal conduc-tion and damage to nonpigmented regions of the hair follicle but retain confinement on the spatial scale of the follicle itself. Second, the efficiency of extracting heat from the epidermis during each laser pulse into cold sapphire in contact with the skin surface should be improved with the longer laser pulse.
The biologic mechanisms by which ruby laser pulses cause permanent loss of terminal hair remain unknown. However, this study strongly suggests that miniaturization of coarse terminal hair follicles to vel-luslike hair follicles is involved, producing nonscarring alopecia. Only 1 participant with laser-induced alopecia was examined histologically 1 year after laser exposure, and more should be studied as the number of people with laser-induced alopecia grows. In this participant, however, there was an absence of fibrosis or any rem-nant of laser-damaged hair follicles, a decrease in termi-nal hair follicles, and a reciprocal increase in miniature hair follicles. These histological findings are also consis-tent with clinical observations. A miniaturized terminal hair or secondary vellus hair is arbitrarily defined as having a cross-sectional hair shaft diameter of less than 30 mm.9Because the size of a hair depends on the size
of the papilla and the hair bulb,16ruby laser pulses seem
to miniaturize the papilla and the bulb either by direct photothermal injury or by injury to other structures of
the follicle that control formation of the bulb with each anagen cycle.
The histological picture of miniaturized follicles after ruby laser pulses corresponds with the histological picture of androgenetic alopecia.8,9,17Male baldness is
characterized by a proportional reduction in size of the papilla and the matrix.16Therefore, the terminal
fol-licles are gradually transformed to velluslike folfol-licles. “Loss” of hair in androgenetic alopecia only relates to the loss of terminal hairs and is similar to “loss” of hair after ruby laser treatment. The follicles are not actually lost but produce hairs that are shorter, finer, and less pigmented. These miniaturized follicles still have arrec-tor pili muscles.8Pluripotent stem cells of the bulge—a
region of follicular epithelium near the insertion of the arrector pili muscles—regenerate epidermis during wound healing.18,19To the extent that ruby laser–induced
alo-pecia is like male pattern aloalo-pecia, wound healing should not be largely affected after laser hair removal.
We hypothesize and suggest that the 2 distinct responses—growth delay and permanent hair loss— are caused by induction of telogen and miniaturization of terminal hair follicles, respectively. Numerous observations are explained by this hypothesis. In all 13 participants, whether they had measurable permanent
Figure 2.Hair loss in a test site on the thigh treated with 60 J/cm23 months
(top) and 2 years (bottom) after treatment. Alopecia is still present at 2 years.
80 60 30 70 40 10 0 50 20
60-S 40-S 30-S Con-S 60-E 40-E 30-E Con-E
% Hair Loss
Fluence, J/cm2
6 mo 1 y 2 y
Figure 3.Hair loss in the 4 participants with clinical alopecia 6 months, 1 year, and 2 years after laser exposure for each fluence (60, 40, and 30 J/cm2) in shaved (S) and epilated (E) sites compared with unexposed control
(Con-S and Con-E) sites.
Histological Findings*
Before Laser Treatment
1 y After Laser Exposure
Terminal hairs, No. 3 1
Velluslike hairs, No. 1 3
Total hairs, No. 4 4
Terminal-velluslike ratio 3:1 1:3
Average (mean±SD) hair shaft diameter, µm
68.7 ± 44.2 22.5 ± 12.2
Fibrous tracts Absent Absent
hair loss or not, there was a growth delay consistent in length with telogen. Presence of the hair shaft during laser exposure was not essential to induce growth delay, which occurred at all fluences in both shaved and epilated sites in all participants.6Presumably,
there is enough ample melanin present because epila-tion typically breaks the hair shaft above, in the upper third of, or at the midlevel of the bulb.20In contrast,
permanent hair loss after a single laser exposure was significant only in sites that were shaved (hair shaft present) rather than wax epilated and was fluence dependent. Both responses are clinically significant and may be separately desirable to different patients. Growth delay that provides a few months of hairless skin is far more reliable and requires lower fluences than permanent hair loss. Permanent hair loss occurred in this study in only 4 of the 13 participants after a single treatment.
Knowledge of the hair cycle and particularly of the length of telogen is essential for interpretation of the results of this study. At present, no consensus exists on a definition for treatment-induced “perma-nent” hair loss despite frequent use of the term to describe the effects of electrolysis. We suggest, and hereby use, the following specific definition: “perma-nent” 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. Telogen may last for 3 to 7 months on the thighs and chest,21,22 after
which the follicle will recycle into anagen, which also lasts 3 to 7 months on the body. Our observation period of 24 months after a single laser treatment therefore spans 2 to 4 complete growth cycles, depend-ing on the length of the telogen phase. The data show gradual reappearance of terminal hair up to 6 months after laser exposure, which is consistent with recovery of terminal hair follicles within 1 growth cycle. Thereaf-ter, the data show no significant difference in hair counts 6 months, 1 year, and 2 years later, which is consistent with no further recovery of terminal hair fol-licles. This strongly suggests that whatever terminal hair follicles were inactivated at 6 months were also missing for at least 2 years, although we did not map and track individual hair follicles in this study. For studies of laser or other treatments intended to induce hair loss, we suggest that measurements be carried out until a steady state is achieved, which in this study seems to be between 6 months and 1 year. A distinction also needs to be made between permanent and com-plete hair loss. Comcom-plete hair loss refers to a lack of regrowing hairs (ie, a significant reduction in the num-ber of regrowing hairs to zero). Complete hair loss may be either temporary or permanent. Ruby laser treatment usually produces complete hair loss for 1 to 3 months, followed by partial permanent hair loss.
Finally, it is likely, but as yet unproven, that the sensitivity of human hair follicles to laser pulses varies with the hair growth cycle. In this study of responses after a single treatment, the hairs “resistant” to perma-nent inactivation by laser treatment may have been mainly in the telogen stage at the time of exposure. On the thighs, up to 72% of the hairs are in telogen.21
Selec-tive photothermolysis requires absorption of light, and the bulb of a telogen hair is unpigmented because of cessation of melanogenesis during catagen.23On the
other hand, as anagen progresses, the bulb and papillae descend deeply into the dermis and beyond such that late anagen hairs may also be relatively resistant to laser pulse injury. By this reasoning, follicles should be most easily inactivated by laser pulses during early anagen. If so, the reliable induction of telogen with a single laser treatment, as we suggest, has profound clinical implica-tions. As the “surviving” terminal follicles transition into anagen, after growth delay, a second treatment may be more effective than the first. On the contrary, a sec-ond treatment given too early or too late may have little effect. We are presently investigating these interesting questions.
Accepted for publication December 8, 1997.
This study was supported by funds from the Wellman Laboratory of Photomedicine, Harvard Medical School, Boston, Mass.
Presented in part at the 1997 American Society for La-ser Medicine and Surgery, Phoenix, Ariz, April 4, 1997.
We thank Thomas Flotte, MD, for his assistance with the histology slides.
Reprints: R. Rox Anderson, MD, Wellman Laborato-ries of Photomedicine, Bartlett Extension 6, 50 Blossom St, Boston, MA 02114.
REFERENCES
1. Kvedar JC, Gibson M, Krusinski PA. Hirsutism: evaluation and treatment.J Am Acad Dermatol. 1985;12:215-225.
2. Richards RN, Marguerite U, Meharg G. Temporary hair removal in patients with hirsutism: a clinical study.Cutis. 1990;45:199-202.
3. Wagner RF. Physical methods for the management of hirsutism.Cutis. 1990; 45:19-26.
4. Kligman AM, Peters L. Histologic changes of human hair follicles after electroly-sis: a comparison of 2 methods.Cutis. 1984;34:169-176.
5. Anderson RR, Parrish JA. Selective photothermolysis: precise microsurgery by selective absorption of pulsed radiation.Science. 1983;220:524-527. 6. Grossman MC, Dierickx C, Farinelli W, Flotte T, Anderson RR. Damage to hair
follicles by normal-mode ruby laser pulses.J Am Acad Dermatol. 1996;35:889-894.
7. Frishberg DP, Sperling LC, Guthrie VM. Transverse scalp sections: a proposed method for laboratory processing.J Am Acad Dermatol. 1996;35:220-222. 8. Whiting DA. Diagnostic and predictive value of horizontal sections of scalp
bi-opsy specimens in male pattern androgenetic alopecia.J Am Acad Dermatol. 1993; 28:755-763.
9. Headington JE. Transverse microscopic anatomy of the human scalp.Arch Der-matol. 1984;120:449-456.
10. Whiting DA. The value of horizontal sections of scalp biopsies.J Cutan Aging Cosmet Dermatol. 1990;1:165-173.
11. Anderson RR, Parrish JA. The optics of human skin.J Invest Dermatol. 1981; 77:13-19.
12. Polla L, Margolis RJ, Dover JS, et al. Melanosomes are a primary target of Q-switched ruby laser irradiation in guinea pig skin.J Invest Dermatol. 1987;89: 281-286.
13. Dover JS, Margolis RJ, Polla LL, et al. Pigmented guinea pig skin irradiated with Q-switched ruby laser pulses: morphologic and histologic findings.Arch Der-matol. 1989;125:43-49.
14. Van Gemert MJC, Welch AJ. Time constants in thermal laser medicine.Lasers Surg Med. 1989;9:405-421.
15. Anderson RR. Laser-tissue interactions. In: Goldman MP, Fitzpatrick RE, eds. Cutaneous Laser Surgery: The Art and Science of Selective Photothermolysis. St Louis, Mo: Mosby–Year Book Inc; 1994:1-18.
16. Van Scott EJ, Ekel TM. Geometric relationships between the matrix of the hair bulb and its dermal papilla in normal and alopecic scalp.J Invest Dermatol. 1958; 31:281-287.
17. Abell E. Pathology of male pattern alopecia.Arch Dermatol. 1984;120:1607-1608.
18. Sun T, Cotsarelis G, Lavker RM. Hair follicular stem cells: the bulge-activation hypothesis.J Invest Dermatol. 1991;96(suppl 5):77S-78S.
19. Lavker RM, Miller S, Wilson C, et al. Hair follicle stem cells: their location, role in hair cycle, and involvement in skin tumor formation.J Invest Dermatol. 1993; 101(suppl 1):16S-26S.
20. Bassukas ID, Hornstein OP. Effects of plucking on the anatomy of the anagen hair bulb: a light microscopic study.Arch Dermatol Res. 1989;281:188-192. 21. Seago SV, Ebling FJB. The hair cycle on the human thigh and upper arm.Br J
Dermatol. 1985;113:9-16.
22. Saitoh M, Uzuka M, Sakamoto M. Human hair cycle.J Invest Dermatol. 1970; 54:65-81.
23. Kligman AM. The human hair cycle.J Invest Dermatol. 1959;33:307-316.
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