A diagnosis under ultraviolet light

A man in his 30s presented with a three month history of an unusual odour from the armpits. On examination, the axillary hair shafts were encircled by what appeared to be soft yellow-white material. The hair roots and adjacent skinwere not affected.Dermoscopywithpolarised light showedyellowish-white creamy concretions adherent to several hair shafts (fig 1, left). Under ultraviolet light (a Wood’s lamp with a wavelength range of 360-400 nm) these concretions exhibited green, purple, and red fluorescence (fig 1, right). The findings represent an atypical example of trichomycosis axillaris, a superficial bacterial infection of axillary hair caused by corynebacterium, which usually fluoresces with pale yellow light under UV dermoscopy. The diagnosis is usually made clinically, but bacterial culture can be used to confirm the causative bacteria. The condition mainly affects young adults, and risk factors include hyperhidrosis and living in areas with high humidity.1 Management includes shaving the affected hair or using topical antibiotics.1