Sebaceous Glands and Sebum
The oil on the surface of skin is a complex mixture of sebum, lipids (from the surface skin cells), sweat and environmental material.
Sebum is produced by sebaceous glands. These are found over most of the body, although there are few on the hands or feet and none on the palms and soles. Sebaceous glands on the mid-back, forehead and chin are larger and more numerous than elsewhere (up to 400-900 glands per square centimetre). They are also numerous in the ear canal and around the genitals.
The sebaceous gland consists of lobes connected by ducts, which are lined with cells similar to those on the skin surface.
Most sebaceous glands open out into the hair follicle. Some free sebaceous glands open directly onto the skin surface. These include Meibomian glands on the eyelids, Tysons glands on the foreskin and Fordyce spots on the upper lip or genitals.
Sebum is produced when the sebaceous gland disintegrates. The cells take about a week from formation to discharge. Sebum is a complex and variable mixture of lipids including:
- Glycerides
- Free fatty acids
- Wax esters
- Squalene
- Cholesterol esters
- Cholesterol
Triglycerides produced by sebaceous glands are broken down by bacterial enzymes (lipases) in the sebaceous duct to form free fatty acids.
Lipase Test (National Institute of Health)
Lipase is a protein (enzyme) released by the pancreas into the small intestines. It triggers the breakdown of fat into fatty acids.
What Does Sebum Normally Do?
Sebum has the following functions:
- It reduces water loss from the skin surface
- It protects the skin from infection by bacteria and fungi
- It contributes to body odour
- It is colonised by the bacteria Proprionibacterium acnes, which may have a role in immune regulation
Hormonal Control of Sebum
Sebum production is under the control of sex hormones (androgens). The most active androgens are testosterone, 5-testosterone (DHT) and 5-androstene-317diol. These hormones and others are made by the sex glands (ovary in females, testis in males) and by the adrenal gland. These glands are in turn under the influence of the pituitary gland, located in the brain.
Androgens are made more active by enzymes in the skin and sexual organs. Type 1 5- reductase acts in the skin and Type II 5- reductase acts in the sexual organs. These enzymes convert less active androgens into the active testosterone and 5-testosterone (DHT). These more active androgens stimulate sebaceous gland cells to produce more sebum.
The role of progesterone is unclear. Females produce more sebum in the week before their menstrual period when progesterone levels are higher. But progesterone is known to reduce the activity of the enzyme 5-reductase that one might expect to reduce sebum production.
Sebum Varies with Age
Sebaceous glands are already active before birth. They are regulated by the mothers hormones and those made by the fetus itself.
The composition of oils on the skin surface varies with age. Excessive sebum production is known as seborrhoea.
- The fetus produces vernix caseosa, a waxy protective layer
- For 3 to 6 months, sebum produced by a newborn baby resembles that of an adult
- Thereafter until the age of 8 it has less wax and squalene and more cholesterol
- Sebum production increases at puberty up to fivefold in men
- Adult males produce slightly more sebum than adult females
- Sebum production declines with age, particularly after menopause in females
The amount of sebum can be altered by disease:
- Pituitary, adrenal, ovarian or testicular disorders may increase or reduce it
- Prolonged starvation reduces the amount of sebum
- Parkinson's disease increases the amount of sebum
The amount can be reduced by certain systemic medications:
- Oestrogens (oral contraceptive pill)
- Antiandrogens such as cyproterone acetate and spironolactone
- Vitamin-A derivatives such as isotretinoin
The amount can be increased by other systemic medications:
- Testosterone given to prepubertal males
- Progesterones with androgenic properties such as medroxyprogesterone, levonorgestrel
- Phenothiazines
The proportion of different components may change with certain medications:
- Diane-35® / Estelle-35®,containing ethinyl (o)estradiol 35mcg and cyproterone 2mg, increases linoleate
- Isotretinoin reduces squalene, wax esters and fatty esters
Barrier Function
linkinghub.elsevier.com/retrieve/pii/S0923181106001733
Skin permeability barrier function is impaired in eczema, particularly in contact and atopic dermatitis (AD). In contact dermatitis disruption of the barrier by irritants and allergens is the primary event, followed by sensitization, inflammation, increased epidermal proliferation and changes in differentiation. Genetically impaired skin barrier function is already present in non-lesional and more pronounced in lesional skin in AD. Increased epidermal proliferation and disturbed differentiation, including changes in lipid composition, cause impaired barrier function in AD. Defective permeability barrier function enables the enhanced penetration of environmental allergens into the skin and initiates immunological reactions and inflammation. Barrier dysfunction is therefore crucially involved in the pathogenesis of AD. The atopic syndrome represents a genetically impaired skin barrier function as well as impaired nasal, bronchial, and intestinal mucous membranes leading to AD, allergic rhinitis, bronchial asthma or aggravation of AD. Common treatment strategies for eczema include the application of lipid-based creams and ointments, which aim toward the restoration of the defective permeability barrier, thus helping to normalize proliferation and differentiation.
Sun Increases Sebum Production
Stimulating Sebum Production
Hormones and Sebum Production
Sebum Protects the Skin from Infection
Reduces Water Loss from the Skin
The underactive oil gland produces inadequate oil secretions that lead to insufficient lubrication of the skin’s surface. Lack of natural sebum diminishes its ability to retain moisture, since oil in the skin acts as a natural barrier against moisture loss. Sebum acts to protect and waterproof hair and skin and keeps them from becoming dry, brittle and cracked by dehydration. It can also inhibit the growth of some microorganisms (such as some bacteria) on the skin.
Delta-6-Desaturase
Ge et al.] also identified human FADS2 as the major fatty acid desaturase in human sebaceous glands capable of catalysing palmitate (C16:0) D6-desaturation to sapienate (C16:1n-10). In human, sapienate is the major fatty acid in sebaceous gland. Thus these authors proposed that FADS2 plays an important role in sebum production, possibly sebocyte differentiation in human and skin homoeostasis.
Citrus Inhibits Sebum Production
General
More on Sebum from Acne Sites
Lactoferrin & Lactoperoxidase: part of a complex of enzymes derived from sugar and whey, which have a remarkable effect on the skin in helping to regulate sebum production and support the skin's natural immune system. They are a non-active ingredient with anti-microbial activity. Potassium Thiocyanate: part of a complex of enzymes derived from sugar and whey. It is a non-irritant ingredient with anti-microbial activities that work to promote normalization of skin sebum.
Moss Extract: from mosses (Phyllum Bryophyta) has sebum regulating and healing properties.
Orange Blossom Hydrosol: Hydrosols are the result of the plant material, when exposed to steam, releasing volatile therapeutic components into the water. The essential oil is drawn off and the hydrosol is left containing micro molecules of essential oil and constituents from the herbal or floral material. Orange blossom hydrosol is an effective sebum regulator for dry or combination skin.
Squalane: a light-weight oil derived from olives, wheat germ or rice bran, squalane is also found in human sebum in quantities around 10%. Hydrogenation of olive-derived squalane gives it stability and enables its use in skin care. It is a luxurious, non-comedogenic, irritation-free oil that the skin readily absorbs due to its similarity to the skin's own sebum.
Glucose Oxidase: a non-irritant active ingredient with anti-macrobial activities. It promotes normalization of skin sebum production. Excellent for acneic skin conditions; significantly reduces blackheads.
What foods help fight acne?
It's really the flip side...more colourful fruits and vegetables, whole grains. Why? These do not spike blood sugar and insulin, they keep it stable...they also carry with them lots of antioxidants that are important for skin protection in acne.
More fish and seafood. Why? Research shows that those who eat the greatest amounts of fish and seafood have the lowest rates of every type of acne blemish...from blackheads to acne cycts. The reason is almost certainly because the omega-3 fatty acids help to turn off the acne inflammation and turn down the dial on sebum production.
Drink green tea. Why? In addition to all its other health benefits, green tea has a natural antioxidant chemical that can trurn down production of an acne-promoting hormone called di-hydrotestosterone. Watch out for vegetable oils, we are currently over consuming omega-6 fats from corn, soybean, safflower and sunflower oils. Why? This type of fat can drive sebum production and inflammation right at the pore level.
http://www.outsmartacne.com/sebum/
Linoleic acid is a natural compound of sebum. Sebaceous glands, found within hair follicles, release sebum to provide lubrication of follicles and surrounding skin. The body requires these essential fatty acids, linoleic and alpha-linoleic acids, more known as Omega-3 and 6.
Studies have discovered links that propose that Trans fats may break down the body's own supply of linoleic and alpha-linoleic acids. This is why acne breakouts are more likely to appear in people that have a deficiency in Omega-3 and Omega-6 oils.
Sebum output begins to be produced with oleic acid that can cause irritation to the skin which is why acne can appear. It has been proposed that oleic acid sebum is drier, stiffer and more prone to cause blackheads, whiteheads and to shape follicular plugs which lead to blemish infections.
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