A paradoxical phenomenon: Intense pulsed light‐induced hypertrichosis, a brief review

Abstract

AbstractThe advancement of laser and light therapies have allowed patients of all races and ethnicities access to different methods for removing unwanted hairs that can cause emotional distress and impact one's quality of life. Despite their effectiveness, these technologies are not without their risks, such as the well‐known side effects of blister formation, erythema, crusting, and postinflammatory hypo‐ and hyperpigmentation. However, one adverse effect that seems to remain a clinical mystery is paradoxical hypertrichosis. Paradoxical hypertrichosis is the growth of fine, dark hair in treated areas or untreated areas close to the area treated on the face and neck, more frequently affecting those with darker skin (Fitzpatrick III‐VI) and darker hair color, and most associated with those having undergone the intense pulsed laser and long‐pulse alexandrite laser, although, this adverse reaction is likely common to all current and laser and light hair removal devices, despite the unknown prevalence and varying incidence rates. This phenomenon is not well understood, although explanations include the activation of dormant hair follicles by the intense pulse light flashlamp's suboptimal fluences and the synchronization of hair growth cycles caused by direct light stimulation.