Erythrasma in a Male's Armpit

Description

Left axilla and adjacent anterolateral chest wall are shown with the arm slightly abducted, exposing the axillary vault and hair-bearing (hirsute) skin of the anterior and posterior axillary folds. Reddish-brown, finely scaly macules coalesce into patches along the deepest portion of the intertriginous crease, where the medial upper arm contacts the lateral thoracic wall. Follicular openings and short axillary hairs remain visible through the discoloration, suggesting a superficial process limited to the stratum corneum rather than a nodular folliculitis or hidradenitis pattern. Erythrasma is classically caused by Corynebacterium minutissimum and favors warm, occluded sites such as the axilla, groin, and inframammary folds, so this view puts the key diagnostic terrain in frame. Under Wood lamp examination, these plaques often fluoresce coral-red due to coproporphyrin III, a practical bedside discriminator from tinea cruris or candidal intertrigo, which more often show an active scaly border, satellite pustules, or maceration. Treatment decisions hinge on recognizing that this is a bacterial intertrigo: topical clindamycin or erythromycin and benzoyl peroxide washes usually suffice, while extensive disease may prompt oral macrolide therapy, plus attention to friction, hyperhidrosis, obesity, and diabetes risk. Dermatology and infectious disease teaching files can pair this image with differential-diagnosis plates for inverse psoriasis, dermatophytosis, and contact dermatitis in the axillary fold. It also fits primary care education on intertrigo workups, including when to use Wood lamp, KOH preparation, and culture, and it supports patient-facing materials on hygiene, antiperspirant use, and recurrence prevention in the underarm. Anatomical accuracy verified by SciePro's Medical Advisory Board.