Acne vulgaris. Artwork showing aspects of acne vulgaris, a skin disorder in which the sebaceous glands in hair follicles become inflamed. Acne vulgaris generally starts in adolescence and is caused by overactivity of the sebaceous glands. The sebum produced by the glands cannot escape as the hair follicles are blocked by a keratin plug. Bacteria (green rods, central panels) multiply and the follicle becomes inflamed. A pustule forms in the sebaceous gland which may rupture releasing fluid (yellow) into the surrounding tissue. Acne vulgaris is found mainly on the face, back and chest. Treatment is with antibiotic drugs and ultraviolet light.