We see our skin everyday and we always read about it being the largest organ of the body, but what exactly does it do? It must do something if it is an organ. What is the role of skin? Here are seven important physiological roles for skin.
1. Regulation of Body Temperature (Thermoregulation). The skin helps the body maintain its desired temperature of 98.6F or 37C. It does this by dilating (opening or enlarging) blood vessels on the surface to release heat, or by constricting blood vessels to retain heat. A second way is by secreting sweat which evaporates on the skin’s surface so that in evaporating it has a cooling effect. Finally, the hypodermis layer of the skin provides insulation to maintain heat. The hypodermis is the deepest layer of skin under the dermis and is composed mostly of fat .
2. Protection. The skin is physical barrier that prevents not only bacteria, viruses, and fungi from entering the body but also keeps most things from the environment or that you put on your skin from entering the body. Yes, you may have heard differently but the skin absorbs very little of what goes on it. This is often called the Skin Barrier Function and it provides a barrier between the inside of the body and the outside of the body. If the skin surface becomes compromised, however, due to abrasion, pathogens and toxin can enter the body more easily.
Besides preventing things from getting into the body, the skin also prevents water from leaving the body thus preventing dehydration. In situations like severe burns to the body, preventing excessive dehydration becomes a major, life threatening challenge.
3. Sensation. The skin is a sensory organ that we use to evaluate the outside environment. Receptors in the skin transmit information on temperature, pain and pressure.  In some cases this can be very enjoyable, even sexual.

4. Excretion. Through the process of sweating the skin can secrete products of metabolism from the body as well as drugs and toxins. The skin also contains enzymes that process toxins helping to break them down.

5. Immunity. Cells of the immune system called Langerhans cells can be found in the skin ready to be called into action when necessary to prevent infection. The skin also participates in the inflammatory response to protect the rest of the body from potential pathogens.
6. Blood Reservoir. Approximately 8-10% of the total blood volume of the body resides in the skin. When necessary this blood can be sent to the skeletal muscles to increase oxygen and nutrients there when needed it is directed to the more central parts of the body to maintain warmth.
7. Endocrine gland.  The skin acts as an endocrine gland by making hormone vitamin D or more specifically vitamin D3 from 7-dehydrocholesterol (7-DHC), a process that requires sunlight or UVB radiation. This vitamin D3 is then sent to the liver for additional processing. Vitamin D is important for the absorption of calcium from the intestines as well as other less defined roles.

Want to learn more about skin physiology? You can purchase our downloadable class notes here.