Armpit of a patient with hidradenitis suppurativa who has been treated with the drug adalimumab (marketed under the name Humira). 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. Adalimumab is a human monoclonal antibody that targets excess tumour necrosis factor (TNF) in the body, overproduction of which causes inflammation, swelling, and pain.