Intralesional injection of the anti-inflammatory steroid triamcinolone acetonide to treat hidradenitis suppurativa in a patients armpit. The injections deliver higher concentrations than topical application. Hidradenitis suppurativa, also known as acne inversa, is caused by the blockage of the apocrine glands typically found in the armpits, buttocks, groin and back. Apocrine glands are specialised sweat glands that open into a hair follicle before reaching the skin. The glands become blocked due to overactivity, giving rise to inflammation, infection and abscess formation. Cryosurgery, antibiotic drugs, surgical excision, grafting or steroid drugs are used in the treatment of this condition.