Sebum is a wax-like oily substance produced in glands just below the surface of the skin. These are called sebacious glands, and open into the hair follicle (the opening through which the hair grows). Sebum in normal amounts is a valuable secretion, which helps to lubricate the skin and keep it supple, and also gives some protection from the outer environment.

Sebum only becomes a problem when there is too little or too much of it, giving rise to dry or oily skin conditions. When the skin is excessively oily, due to over-production of sebum, the hair follicles may become blocked by excess sebum combined with dirt and particles of dead skin cells flaking away at the surface. Bacteria feed on the plug of sebum and debris, and the hair follicle becomes inflamed and infected and a 'spot' is produced. When an area of skin is affected by a number of spots (more correctly called pustules) and this condition persists, it is known as acne.

Over production of sebum is common in adolescents, when the whole hormonal system is going through a stage of upheaval, though people whose skins are oily in youth will often retain a normal and attractive skin texture far longer than those whose skin was dry in youth, since sebum production declines with age.

Balancing of the sebum production by means of treatments with essential oils is one of the most effective ways of dealing with over- or under-production. Two or three oils, most notably geranium and lavender, have the property of balancing both over- and under-production of sebum, and so can be used to help both excessively dry and very greasy skins.

Among the oils which are useful for correcting very oily skins, the most effective is Bergamot, followed by Juniper and Cedarwood. To help with over-dry skins, lacking in natural lubrication, Camomile, Jasmine, Neroli and Rose oils are all good choices, but the best of all is probably Sandalwood. Any of these oils can be used, preferably as a facial massage oil, but also in creams and lotions for use between massage treat­ments. For dry skins a very emollient carrier oil, such as oil of avocado or peach kernel oil, is very helpful.

See also SKIN.