Painful Bilateral Gynecomastia Secondary to Topical Finasteride

A 76-year-old man developed grade three gynaecomastia with breast tenderness after using 0.25% topical finasteride for male pattern hair loss for 11 months. The symptoms resolved after stopping the treatment, although the breast enlargement persisted. This case is notable as it is the first reported instance of gynaecomastia linked to topical finasteride, a condition more commonly associated with oral finasteride. The condition is thought to result from increased conversion of testosterone to oestradiol, raising oestrogen levels. Gynaecomastia is rare with topical finasteride and was not observed in phase three clinical trials.