Inflamed sebaceous cyst. This adult male has an infected sebaceous cyst on the nape of his neck (at centre). The raised, pink lesion has a pale centre where pus is collecting. Sebaceous cysts arise from the blockage of secretory glands (producing oily sebum) which surround a hair follicle. The cyst becomes filled with a smooth, yellow, cheesy material which may get infected by bacteria and become painful. Treatment is by surgical removal of the cyst wall under local anaesthetic. Antibiotic drugs will prevent infection.