[2] In humans, sebaceous glands occur in the greatest number on the face and scalp, but also on all parts of the skin except the palms of the hands and soles of the feet.

Fordyce spots are benign, visible, sebaceous glands found usually on the lips, gums and inner cheeks, and genitals.

In humans, sebaceous glands are found throughout all areas of the skin, except the palms of the hands and soles of the feet.

[4] Sebaceous glands are also found in hairless areas (glabrous skin) of the eyelids, nose, penis, labia minora, the inner mucosal membrane of the cheek, and nipples.

Overexpression of the signalling factors Wnt, Myc and SHH all increase the likelihood of sebaceous gland presence.

[6] Relative to keratinocytes that make up the hair follicle, sebaceous glands are composed of huge cells with many large vesicles that contain the sebum.

Sebaceous glands secrete the oily, waxy substance called sebum (Latin: fat, tallow) that is made of triglycerides, wax esters, squalene, and metabolites of fat-producing cells.

In colder conditions, the nature of sebum becomes more lipid, and in coating the hair and skin, rain is effectively repelled.

[25] During the last three months of fetal development, the sebaceous glands of the fetus produce vernix caseosa, a waxy white substance that coats the skin to protect it from amniotic fluid.

[27] Meibomian glands, in the eyelids, secrete a form of sebum called meibum onto the eye, that slows the evaporation of tears.

[28] They also serve to create an airtight seal when the eyes are closed, and their lipid quality also prevents the eyelids from sticking together.

Acne is a common occurrence, particularly during puberty in teenagers, and is thought to relate to an increased production of sebum due to hormonal factors.

Comedones generally occur on the areas with more sebaceous glands, particularly the face, shoulders, upper chest and back.

Comedones may be "black" or "white" depending on whether the entire pilosebaceous unit, or just the sebaceous duct, is blocked.

[41]: 22–25 viii  Astruc describes them being blocked by "small animals" that are "implanted" in the excretory ducts[41]: 64  and attributes their presence in the oral cavity to apthous ulcers, noting that "these glands naturally [secrete] a viscous humour, which puts on various colours and consistencies... in its natural state is very mild, balsamic, and intended to wet and lubricate the mouth".

[41]: 85–86  In The Principles of Physiology 1834, Andrew Combe noted that the glands were not present in the palms of the hands or soles of the feet.