Sebum is composed of lipids (oil) and contributes to the face’s skin barrier function. It protects the skin from damage, especially UV-induced oxidation as well as prevents transepidermal water loss. With hyperseborrhoea, or excess sebum, the skin tends to present a shine throughout the day either in the T-zone or over the entire face. Unsuitable or poorly used cosmetics (too rich, too stripping) and sun exposure without protection can encourage excess sebum production. In adulthood, causes include pollution, smoking, stress and fatigue. In teenagers, hormones play a role.