Sebum is an oily, waxy substance secreted by microscopic sebaceous glands in the skin. It coats, moisturizes, and protects the skin, playing a part in its overall health. The amount produced varies significantly between individuals, which is why some people experience oily skin while others have dry skin.
Sebum Production and Composition
Sebum originates from the sebaceous glands, which are found across most of the body’s surface. These glands are most concentrated on the face, scalp, and chest, which is why these areas are often more prone to oiliness. The skin on the face can have as many as 900 sebaceous glands per square centimeter. The only areas completely devoid of these glands are the palms of the hands and the soles of the feet.
Sebum is a complex mixture of lipids. The primary components of human sebum are triglycerides and their associated fatty acids, which make up about 57.5% of the mixture. Following these are wax esters at 26% and a lipid called squalene at 12%. This composition provides sebum with its characteristic oily texture and its ability to form a protective layer on the skin’s surface.
The Protective Role of Sebum
A primary function of sebum is to moisturize and waterproof the skin and hair. It forms a thin, protective film that locks in moisture, preventing the skin from becoming dry or brittle. This same coating action applies to hair, helping to keep it soft and hydrated. Without this lubricant, skin would lose water too quickly, leading to dehydration.
It is a component of the acid mantle, a slightly acidic film on the skin’s surface that acts as a primary line of defense. This mantle helps to maintain the skin’s pH, which is naturally between 4 and 6. This acidic environment is inhospitable to certain harmful pathogens, such as some bacteria and fungi, protecting the skin from infections. Furthermore, sebum transports fat-soluble antioxidants like vitamin E to the skin, which can help shield it from environmental damage.
Factors Influencing Sebum Levels
Several internal factors influence sebum production. Hormones, particularly androgens, are primary regulators. Androgens are often referred to as male hormones, but they are present in both sexes. An increase in androgen levels, such as during puberty, signals the sebaceous glands to mature and produce more sebum, which is why oily skin and acne are common during teenage years.
Age also influences sebum production. After the surge in puberty, production levels remain steady through early adulthood but begin to decrease over time. This gradual decline is one reason why older individuals often experience drier skin. Genetics are another determinant, as the tendency to have oily or dry skin often runs in families.
Sebum Imbalance and Skin Health
Both overproduction and underproduction of sebum can lead to common skin concerns. An excessive amount results in oily skin, characterized by a greasy or shiny appearance. This excess oil can combine with dead skin cells and other debris, leading to clogged pores. These clogged pores create an ideal environment for bacteria to thrive, which can contribute to the formation of acne, including blackheads and pimples.
Conversely, an insufficient amount of sebum can compromise the skin’s protective barrier. This leads to dry, flaky, and sometimes itchy skin that can feel rough to the touch. When the skin lacks its natural oils, it loses moisture more readily and becomes more vulnerable to external irritants and environmental stressors. This can exacerbate conditions like eczema.