J. Soc. Cosmetic Chemists 16 405-411 (1965) ¸ 1965 Society of Cosmetic Chemists of Great Britain The Sebaceous Glands F. j. EBLING* Based on a lecture delivered before the Society on 25th February 1965. Synopsis--The structure, mode of secretion, distribution and development of the sebaceous glands are reviewed, the composition of sebum is described, and its function is debated. The actions of androgens, oestrogens, and progestogens on the sebaceous glands are discussed. It is concluded that while traditional views of the function of the sebaceous gland may be challengeable, the gland is far from vestigial in structure and, moreover, its sensitivity to male hormones is no less than that of the accessory male sexual organs. For these reasons a functional status for the gland ought to be assumed, though it is possible that this is not yet fully understood. INTRODUCTION The human scalp and face may have as many as 900 sebaceous glands in each sq cm of skin (1). These glands produce a waxy secretion known as sebum, and in adults about 100 •g cm•/hr of lipid material can be removed from the forehead by absorption on pads of cigarette paper (2-4). Thus a single forehead, say 100 cm • in area, produces nearly 2g of sebum in a week. What is sebum ? What is its function ? How it is produced and how is the activity of the sebaceous gland controlled ? STRUCTURE, MODE OF SECRETION, DISTRIBUTION AND DEVELOPMENT OF SEBACEOUS GLANDS The sebaceous gland is holocrine its secretion is formed by complete disintegration of the glandular cells. In man the gland consists of a series of lobes or acini, each connecting to the main sebaceous duct which itself normally opens into the pilary canal (1) in rodents the gland consists only of one or two simple sacs. Sebaceous cells are replaced by cell division at the periphery of the lobes, and the cells differentiate and disintegrate as *Department of Zoology, The University, Sheffield, 10, Yorks. 405

406 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS they move towards the centre of the lobe and duct. In the human gland, the lobes are in different states of maturity it seems that new acini constantly arise from walls of the duct, grow into sebaceous units, fuse with adjacent lobes, and ultimately degenerate (1). Sebaceous glands occur over much of the body, though not normally on the palms or soles, and only sparsely on the dorsal surfaces of the hand and foot they are largest and most numerous in the mid-line of the back, on the forehead and face, in the external auditory meatus and on the ano- genital surfaces (1). In a number of sites sebaceous glands open directly to the surface of the skin and not by way of a hair follicle. Examples of such glands are the Meibomian glands of the eyelid and Tyson's glands of the prepuce (1). Free sebaceous glands are also found in the areolae of the nipples and along the red margin of the upper lip (5). In the last site such glands are often visible to the naked eye as pale yellow bodies which vary in size from minute specks to about 1.5 mm in diameter. These are known as Fordyce's spots, and appear to increase in number with age. Large sebaceous glands not associated with hair follicles occur in many mammals (6). Such are the flask-shaped preputial glands- opening by single ducts alongside the urethra- of rodents, the inguinal glands of rabbits, the dorsal gland of kangaroo rats (7), the large supracaudal gland of guinea pigs (8), the abdominal glands of shrews, the intermandibular sebaceous glands of bats and pigs (6), the large "brachial glands", one on the ventral surface of each shoulder, of male lemurs (6), and glands in the cloacal region of marsupials (9). In the human foetus the sebaceous gland can be seen, as a small knob on the mid-posterior wall of the developing hair follicles, by 17 weeks of age (10). It is interesting to note that each developing follicle carries an apocrine sweat gland as well as a sebaceous gland, but the apocrine gland subsequently disappears except in a few regions of the body. THE COMPOSITION AND FUNCTION OF SEBUM Sebum is a complex mixture of lipid substances, and its detailed chemical composition is still incompletely known. Information which is available is based not on pure sebum, but on the mixture of sebum and epidermal lipids which makes up the surface film. As much as 30 per cent of the skin surface fat may consist of free fatty acids. Though more than half of these are saturated and unsaturated C, and C, acids, there is a wide range including branched and unbranched