The sebaceous glands are microscopic exocrine glands in the skin that secrete an oily or waxy matter, called sebum, to lubricate and waterproof the skin and hair of mammals. In humans, they are found in the greatest number on the face and scalp, and are also found on all parts of the skin except the palms of the hands and soles of the feet. The type of secretion of the sebaceous glands is referred to as holocrine. In the eyelids, meibomian glands, also called tarsal glands, are a type of sebaceous gland that secrete a special type of sebum into tears. Fordyce spots are ectopic (misplaced) sebaceous glands found usually on the lips, gums and inner cheeks. Areolar glands surround the female nipples. Preputial glands also known as Tyson’s glands are found in the genitals of both sexes of mice and rats. There are several related medical conditions, including acne, sebaceous cysts, hyperplasia and sebaceous adenoma. These are usually attributable to overactive sebaceous glands which produce an excess of sebum.