The skin is the largest organ of the body and the border between the body and the outside world. When it is damaged, several of its jobs fail at once.
Barrier
Keratin, tight cell layers and a thin film of oil keep water in and microbes out. Its slightly acidic surface and normal skin bacteria also slow the growth of harmful germs.
Temperature control
When the body is hot, skin vessels widen and sweat glands release sweat to lose heat. When it is cold, skin vessels narrow to keep warm blood in the core.
Sensation
Nerve endings in the skin sense touch, pressure, vibration, heat, cold and pain. This warns the body of danger, such as pressure from lying still too long.
Vitamin D and immunity
Sunlight on the skin starts the making of vitamin D, needed to absorb calcium. Immune cells in the skin catch invaders and alert the rest of the immune system.
At the bedside
Skin color, temperature and moisture are a quick window on circulation: cool, pale, clammy skin can be an early sign of shock. Patients who lose large areas of skin, as in major burns, lose fluid and heat fast and are at high risk of infection.
Related guides
Written by Making Synapses. Topic reference: OpenStax, Anatomy and Physiology 2e (no text adapted).