Reduction of regrowing hair shaft size and pigmentation after ruby and diode laser treatment

Laser pulses which selectively damage pigmented hair follicles are a useful treatment for hypertrichosis. Clinically, regrowing hairs are often thinne r and lighter after treatment, In this study, hair shaft diameter and optic al transmission (700 nm) were measured before and after ruby (694 nm) and d iode (800 nm) laser irradiation. Hair was collected from 47 and 41 subjects treated with ruby (0.3 ms and 3 ms) and diode (10-20 ms) lasers, respectiv ely. "Responders" were defined as subjects with significant long-term hair loss as determined by hair counts at 9 and/or 12 months after treatment. In ruby laser responders (34/47), regrowing hairs were significantly both thi nner (decreased diameter) and lighter (increased transmission), In "nonreep onders" (13/47), regrowing hairs were lighter, but not thinner. The regrowi ng hair shaft absorption coefficient (as calculated assuming Beer's law) wa s significantly decreased by 0.3 ms ruby laser treatment, but was not chang ed by 3 ms ruby laser or diode laser treatment. After diode laser treatment , 38 of the 41 subjects were responders and regrowing hairs mere both thinn er and lighter. These results show that laser treatments can affect structu ral recovery (size of hair), follicular pigmentation (hair absorption coeff icient), or both. Regrowth of thinner hair (decreased shaft diameter) occur s in conjunction with actual loss of hair. After long pulses (3 ms ruby; di ode), regrowing hair was thinner and also lighter to an extent related to t he decrease in hair diameter, In contrast, short ruby laser pulses (0.3 ms) appeared to be capable of inhibiting follicular pigmentation per se, in ad dition to affecting the hair diameter. This may account for the complete re growth of lighter hair in "nonresponders'' treated with 0.3 Iris pulses, La ser-induced reduction in hair diameter and/or pigmentation are both long-te rm responses which confer cosmetic benefits in addition to actual hair loss .