The application of PDT to the field of hair removal is in its nascent stages of development. As discussed in the acne section earlier, studies have demonstrated uptake of ALA into the pilosebaceous unit. In 1990, Divaris and colleagues demonstrated that intraperitoneal injection of ALA resulted in PpIX fluorescence in sebaceous glands and to a lesser extent in hair follicles of albino mice . Following illumination, a persistent reduction in the number of hair follicles was observed . Identification of PpIX fluorescence was subsequently reported in mice following topical ALA application  . Recently, PDT induced damage to not only sebaceous glands, but also to hair follicles in a rat model following application of liposomal ALA and irradiation with a red filtered halogen lamp was demonstrated . Liposomal delivery of topical ALA to intact or depilated rat skin demonstrated PpIX expression in pilosebaceous units, with maximal expression in anagen hair. Inhibition of hair induction after depilation was observed .
It is plausible that ALA application topically to depilated skin may facilitate uptake and conversion of ALA into PpIX in hair follicles, making the matrix cells amenable to light destruction. The wavelength would need to be in the red range in order to achieve adequate penetration depth. This would unfortunately be likely to cause the side-effect profile reported extensively for red wavelengths when used with ALA for the treatment of
acne; namely, blistering, crusting, and dyspigmentation. It would be interesting to observe whether short incubation ALA and short durations of illumination would be adequate for hair reduction, while ameliorating side effects.
The only published clinical study regarding the use of PDT for hair disorders in humans aimed at treating the hair-loss disease, alopecia areata with topical ALA followed by red light. This study demonstrated no increase in hair growth following treatment, which would be expected, should PDT to hair follicles result in their destruction . Clearly, clinical studies are needed in order to evaluate this potential modality as a mode of hair removal.
The author has conducted an experimental protocol to evaluate topical 5-ALA and IPL (580-980 nm) for the removal of blonde and gray hair. A photographic example of a patient with excessive vellus hair on the face, prior to and following ALA PDT with IPL is shown in Fig. 21.4. Regrowth following treatment increased from an estimated 30% at 1 month (Fig. 21.4A) to 40% at 2 months (Fig. 21.4B), and 50% at 3 months follow-up (Fig. 21.4D).
It will be necessary to follow patients for a long term—6 months and 1 year—in order to make an assessment regarding long-term reduction.
Basic science studies indicate that topical ALA results in preferential accumulation of PpIX in hair follicles, with highest expression during the anagen phase. This makes actively growing hair susceptible to light-mediated destruction, as shown in rodent models. Clinical studies are needed in order to determine whether this would be a viable mode of hair removal, provided the protocol is optimized to maintain the efficacy of hair follicle destruction without the risk of significant side effects and complications.