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Your skin is the largest organ of your body. It covers the outside of the body, but is also found inside, covering internal organs and lining passage-ways (this skin is called the mucous membrane). It has many functions.
- It protects the body and its internal organs from injury and is a barrier to infection and parasites.
- It helps control the loss of water, and body temperature.
- Waste substances are released as salts through the sweat glands.
- It conducts the sensations of touch, heat, cold, and pain.
- It stores food and water, and makes and stores vitamin D.
The skin is made up of three main layers. The surface layer is called the epidermis. The layer beneath is the dermis, and below that is the fat layer.
(Note on scale: The epidermis and dermis are between 2 and 4 millimetres, depending on the part of the body.)
Skin cancer begins in the epidermis.
The epidermis
The epidermis contains cells that are constantly dividing at the deeper levels, allowing the skin to grow, renew and repair itself. The cells push upwards, stacking up to the skin’s surface. As they rise, they become scalier, harder and flatter. The changing cells create several layers to the epidermis.
The outermost layer is called the stratum corneum, and consists of scaly squamous cells. It is covered by a horny outer layer of skin cells that have died and that will be shed. This is the layer that mostly makes the skin waterproof.
The next layer is called the prickle cell layer. It is a strengthening layer in the skin. These cells can divide, allowing the skin to grow and repair itself. It includes cells that help the body to fight infection.
The lowest layer is the basal cell layer where cells called keratinocytes are found. The keratinocyte is the basic cell of the epidermis. These are the cells that continually divide and push upward. As they rise, they are modified, and replace the cells of each of the other layers of the epidermis as they die. Between the basal cells are the melanocytes. These are the cells that produce the melanin pigment, which gives skin its colour and protects it from the ultraviolet rays of the sun. The pigment is transferred to neighbouring cells and absorbed into all the other layers of the epidermis. Melanocytes may also have a role in fighting infection.
A mole (naevus, beauty spot) is the result of an overgrowth of melanocytes. Moles may be raised or flat, light or dark brown, rough or smooth.
The dermis
The dermis is the sensitive layer of the skin, containing the nerve endings. It is much thicker than the epidermis. It is made up mostly of connective tissue (collagen), which binds and gives support, flexibility and strength to the skin. The dermis carries the blood vessels and lymph vessels. The roots and muscles of our hair are in the dermis. So are the oil glands which make moisturiser for our skin, and the sweat glands, which help to keep us cool. The oil and sweat reach the surface through tiny openings called pores.
The fat layer
The fat layer is the deepest layer of the skin. It keeps body heat in and helps to protect the internal organs.
Information about skin from the British Association of Dermatologists.
