Your skin consists of two main layers:
The outer layer, known as the epidermis and the inner layer, known as the dermis.
The epidermis is the outer layer of your skin and includes the part of your skin you see every day – the surface. However, the epidermis is comprised of more than just the skin's surface. It consists of a number of levels, each with their own distinct role.
Cells in the deepest level of your epidermis are extremely active and divide constantly to make more and more new cells.
Once generated, these new cells are pushed upward through the other levels of the epidermis and toward the surface of your skin. Along the way, they die and eventually become filled with keratin, a very strong protein. These dead, keratin-filled cells make up the outer parts of the epidermis and provide your body with the tough, protective overcoat it needs to survive.
The dead cells on the outer parts of your skin are constantly shed and replaced by new ones. As a result, every 20-30 days, your body has an entirely new surface of skin.
The dermis is the inner layer of your skin. It is a thick layer of connective tissue and is itself divided into two levels. The upper level of the dermis, known as the papillary region, is made of loose connective tissue, while the lower level, called the reticular layer, is comprised of tissue that is more tightly packed.
Your dermis consists of strong collagen and elastic fibres pierced by blood vessels. These blood vessels help regulate the temperature of your body by increasing blood flow to the skin when you are hot and need to release some heat, or by restricting blood flow to the skin when you are cold and need to keep warm.
The dermis includes a network of nerves and receptors that help you sense touch, pressure and pain, and it is also full of hair follicles and sweat and oil glands, which are designed to keep your skin soft and healthy.
As well as performing all of the roles described above, the dermis acts as a cushion against injury. When you cut yourself, the dermis heals by forming new tissue, which is rich in new blood vessels and cells. It is this tissue which helps pull the edges of a cut on your skin back together over the course of 1 to 3 weeks.