Sebaceous glands sebum from

Microcomedo—Microscopic lesion formed from the combination of sloughed, clumping keratinocytes reacting with sebum and fatty acids from the sebaceous gland. 

Most lipids found on the hair surface come from sebum. Hair also contains internal lipids, which are partly extractable [2,3] much of this extractable material also appears to originate from the sebaceous glands. Robbins [2,3] has reported that the total extractable lipid can be as much as 9% of the total weight of hair that has not been shampooed for a week. The external and internal lipids are divided roughly equally among this extractable material. 

Similar to mouse models that lack the acyl-CoA cholesterol acyltransferase-1, diacyl-glycerol acyltransferase-1, and ElovlS genes, Scdl mice exhibit cutaneous abnormalities with atrophic sebaceous glands and narrow eye fissure with atrophic meibomian glands, suggesting an important role of MUFA in skin and eyelid homeostasis. The major function of sebaceous and meibomian glands is to secrete lipid complex lubricants, termed sebum and mebum, respectively. These lubricants contain wax esters, TGs, and cholesteryl esters, and prevent the evaporation of moisture from the skin and the eyeball. 

Lipid extracted from human hair is similar in composition to scalp lipid [134]. Thus, the bulk of the extractable lipid in hair is free lipid however, cell membrane complex lipid is also partially removed by extraction of hair with lipid solvents or surfactants. In a sense, the scalp serves as a lipid supply system for the hair, with sebum being produced continuously by the sebaceous glands [135]. Sebum production is controlled hormonally by androgens that increase cell proliferation in the sebaceous glands, and this in turn increases sebum production [135,136], although seasonal and even daily variations in the rate of sebum production do occur [137]. 

Healthy, normal human skin is kept moist by natural body oils contained in sebum, a secretion of the skin s sebaceous glands. The oily sebum helps the epidermis, or outer layer of the skin, retain the 10-30% of water it normally contains. However, some people suffer from skin that is nam-rally dry, or dry because of aging or contact with materials like paint thinner that dissolve and remove the sebum. Such individuals may find some relief by using OTC products called moisturizers. 

The composition of human skin surface lipids varies over the body but in sebaceous gland-enriched areas (such as the face) the secretion, sebum, may represent 95%. When sebum is freshly formed it contains mainly triacylglycerols, wax esters and squalene. However, due to bacterial action, unesterified fatty acids are rapidly released. These acids are both irritant and comedogenic (give rise to black-heads ) and have been implicated in acne vulgaris - an extremely common complaint of puberty. It is often stated that the severity of acne correlates with the amount of seborrhoea and many treatments are designed primarily to remove epidermal lipids from the skin surface. 

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