Hair removal using lasers or broadband intense pulsed light has become one of the most ubiquitous medical procedures. At our center a small proportion of patients have spontaneously reported what they believed to be increased hair growth at sites of previous laser epilation. We sought to retrospectively review the prevalence and features of this paradoxical effect.

This was a single center, retrospective study that included all patients who underwent laser hair removal during a 4-year period with a long-pulsed alexandrite laser. All cases of laser-induced hypertrichosis were assessed clinically by history, examination, and laboratory tests, and confirmed by review of serial clinical photographs taken during the course of the laser treatments. The clinical features of patients with postlaser hypertrichosis were compared with 50 patients randomly selected from among all those who had undergone laser hair removal at our center (n=489).

Of 489 patients, 3 (0.6%, 95% confidence interval: 0.01-1.9%) treated with the long-pulsed alexandrite laser (755 nm) reported increased hair after laser hair epilation. There was a trend for this adverse effect to occur in darker skin phototypes (IV) and with black hair as compared with the unaffected comparison group (n=50). However, the small number of cases (n=3) did not provide sufficient power to adequately test factors such as age, sex, treatment settings, and number of treatments statistically.

Postlaser hair removal hypertrichosis is a real but rare occurrence in our experience.