THE ROLE OF MOISTURIZERS IN ITCH AND DRY SKIN

Moisturizers and emollients have been used for years in patients with dry skin with some relief in pruritus. Moisturizers are one of the gold standards of treatment in atopic dermatitis, the hallmark

of itchy dry skin.⁴⁰ Moisturizers’ mechanism of action involves retention of water in the stratum corneum and providing an exogenous barrier to prevent transepidermal water loss. However, the antipruritic mechanism of this treatment remains unclear. Moisturizers containing salicylic acids are known to exert anti-pruritic effects with an uncertain mechanism.⁴¹ Moisturizers such as urea, glycerol, and lactic acid promote desquamation and corneodesmolysis. In dry skin, it is likely that abnormal retention of these cohesive proteins coupled with reduced hydration will alter the mechan-ical properties of the stratum corneum. This alteration may lead to the stimulation of underlying nerve fibers in the epidermis.

Importantly, not all moisturizers provide the same effect in restoration of the barrier function.

Certain lipid mixtures or an inadequate concentration of physiologic lipids actually have been demon-strated to inhibit barrier restoration.^42,43Newer ceramide-dominant emollients have been developed in efforts to restore the intrinsic physiologic lipid concentration of the skin. One type of ceramide-dominant emollient was shown to significantly improve the overall severity of atopic dermatitis and demonstrated correction of transepidermal water losses in these patients.⁴⁴ Unfortunately, studies using ceramide-dominant emollients for patients with atopic dermatitis did not use itch improvement as an endpoint. However, these types of moisturizers likely have a role in the improvement of itch associated with dry skin.

In addition to using moisturizers to improve barrier function with hopes of itch reduction subsequent to this improvement, another approach is to formulate topicals containing both mois-turizers and anti-pruritics. Some common topical pruritics currently being used with success are pramoxine and polidocanol.^1,45This approach has been used extensively internationally, but remains underutilized in the United States. Studies using ceramide-dominant emollients compounded with anti-pruritics would be of interest.

12.6 CONCLUSION

The association between primary and secondary causes of dry skin with pruritus is well known.

The mechanism of itch transmission as a result of dry skin and barrier impairment is not as clear.

However, a large body of evidence suggests that a cross-talk exists between the stratum corneum and nerve fibers in the epidermis. This cross-talk through an array of possible mediators is the likely process of itch transmission to the central nervous system. Future studies focused on this interaction will help shed light on the mechanisms of itch stimulation in dry skin. Currently, the treatment of itch using moisturizers is limited. Newer ceramide-dominant emollients and concomitant moisturizer and anti-pruritic formulations offer promise. Future investigations may offer specific topical targets and greatly improve the efficacy of topical therapy.

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