Ruby laser-assisted hair removal success in relation to anatomic factors and melanin content of hair follicles

Ruby laser-assisted hair removal is thought to work tia selective photother molysis, which relies on light reaching the deeper layers of skin, and the absorption of light by the target chromophore, melanin. It is therefore pos sible that efficacy of treatment is affected by anatomic factors that deter mine the amount of light reaching the hair bulbs (i.e., skin color, depth o f intracutancous hair, epidermal thickness and dermal density) and the mela nin content of hair. To examine this hypothesis, a prospective study was pe rformed. Forty-eight volunteers were treated with the Chromos 694 Depilatio n Ruby Laser at a single standard fluence of 11J/cm(2). Treatment efficacy was determined by measuring hair density at 3 and 7 months after treatment. Epidermal depth and dermal density were measured from 2-mm biopsies taken before treatment, and the intracutaneous hair length was determined fr om p lucked hair. Skill color was assessed using a spectrophotometer, and melani n content of dissolved hair was assessed using spectrophotometry. Efficacy of treatment for each patient was compared with the patient's age, intracut aneous hair length, epidermal depth, dermal density, skin color, and total melanin content and relative eumelanin content of hair. No correlation was found between the efficacy of treatment and age and the various anatomic fa ctors. Patients with higher eumelanin content in their hair had better long term results (Spearman rank test, p = 0.00219). The results suggested that the efficacy of treatment did not depend solely on the amount of laser ligh t penetrating the skin but correlated well with the eumelanin content of ha ir. The clinical implication of this finding is discussed.