Background The aim of this study is to investigate the cellular mechanism of long-term hair reduction using a novel, square pulse, low-fluence home-use IPL device.
Methods Ten subjects’ axillae (Fitzpatrick III–V) were treated once weekly for four consecutive weeks in a simulated home-use trial. Treated and control site punch biopsies were taken from axillary sites for H&E staining and blinded histological examination before, immediately after and six months after the fourth treatment. The contralateral axilla served as a control.
Results Histologically, four sequential weekly treatments gave a significant increase in telogen compared with anagen follicles. Six months after the fourth treatment, an 87% reduction in terminal hair count (P ≤ 0.00005) was recorded. An atypical telogen with infundibular dilatation and plugging of keratin and clumping of melanin with disintegration and/or retraction of the intraluminal hair shaft were observed. The papillae remained viable and some new anagen follicles were evident after four treatments. Vellous hairs appeared unaffected by IPL exposures. A mixed inflammatory infiltrate of lymphocytes and eosinophils around vessels of the superficial and deep dermis was sometimes present but the epidermis appeared always normal.
Conclusion A highly significant hair density reduction through induction of telogen followed by miniaturization similar to that achieved in professionally delivered permanent laser hair reduction appears to be the major mechanism of hair reduction using home-use IPL. IPL-induced damage to the isthmus and upper stem may inhibit or interfere with the hair regrowth process. Longer term studies are required to determine if this observed damage is clinically permanent.