Photodynamic Therapy for Hair Removal

The photodynamic therapy (PDT) is based on the principle of light interaction with a pho – sensitizing molecule resulting in the formation of chemically reactive species in the target tissue. However, the phosensitizer must preferentially accumulate in the target tissue to avoid collateral damage. For topical PDT, aminolevulonic acid (5-ALA) was the first mol­ecule demonstrated to have practical usefulness [80]. Topically applied ALA is metabo­lized by viable cells into protoporphyrin IX (PplX), a molecule extremely sensitive to light around 415 nm. Upon excitation to light, PplX produces reactive oxygen species and free radicals that cause localized tissue damage [81]. The advantage of ALA for hair reduction is that the topically applied ALA gets metabolized to PpIX by the rapidly proliferating hair follicle cells at a rate that is much greater than the epidermal cells. Moreover, since the metabolic activation is not dependent on hair color, it makes ALA an ideal molecule for the PDT of gray and blonde hair, which otherwise exhibit poor efficacy to the laser hair-re­moval treatments. Grossman et. al. [82] studied topically applied ALA in a hirsute subject, and demonstrated good efficacy. However, dermal phototoxicity is still a significant safety concern for the use of ALA or any other phosensitizer molecule for hair-removal purposes.