Skin is the largest organ of the human body. It covers the body entirely and is comprised of primarily two layers. The outermost or upper layer of the skin is called the epidermis (this is the part that we see, feel and touch). The epidermis, which consists of several layers, is mostly made of dead epithelial skin cells. Directly beneath the epidermis, is the other primary skin layer, which is called the dermis. This layer has small blood vessels, nerve endings, oil and sweat glands, and hair follicles. The dermis also contains collagen and elastic tissue, which function to keep the skin firm and strong. There is an extra layer underlying the dermis called the subcutaneous layer, which is made up of fatty tissue that acts as a foundation for the dermis.
Skin has four main functions, as follows:
- Protection: As the first line of defense against the external environment, the epidermis is continuously replenishing and shedding tens of thousands of dead cells every minute to protect the body from:
- Mechanical impact: Skin acts as the first physical barrier to withstand any pressure, stress or trauma. When this mechanical impact is stronger than the skin, a wound will occur, as a breakage through skin with loss of one or more of the skin functions.
- Fluids: Due to the tight packing of cells in the outermost layer of the epidermis (the stratum corneum layer), our skin helps us retain necessary body fluids and moisture, and protects us from the absorption of external fluids or liquids. We can bathe, swim and walk in the rain without concern. Our skin prevents the absorption of any harmful substance or excessive water loss through skin.
- Radiation: If it weren’t for the skin, the ultraviolet light (UV light) radiating from sun would damage the underlying tissue in our bodies. This protection is provided by the melanin pigmentation in the epidermis. The skin and its pigmentation helps protect us from many medical illnesses like skin cancers, but because it doesn’t offer complete protection, we should avoid excessive exposure to sunlight by using sunblock and adequate clothing.
- Infections: The top layer of skin is covered with a thin, oily coat of moisture that prevents most foreign substances or organisms (such as bacteria, viruses and fungi) from entering the skin. The epidermis also has Langerhans cells, which help to regulate immune responses to pathogens that come into contact with the skin.
- Thermal regulation: Temperature regulation is aided by the skin through the sweat glands and blood vessels in the dermis. Increased evaporation of the secreted sweat decreases the body temperature. Vasodilation (relaxing of small blood vessels) in the dermis makes it easier for the body to release some heat and lower the body temperature through skin. In vasoconstriction (contracting small blood vessels), the dermis retains some of the internal body temperature. The fatty subcutaneous layer of the skin also acts as an insulation barrier, helping to prevent the loss of heat from the body and decreasing the effect of cold temperatures.
- Sensation: An important function of the skin dermis is to detect the different sensations of heat, cold, pressure, contact and pain. Sensation is detected through the nerve endings in the dermis which are easily affected by wounds. This sensation in the skin plays a role in helping to protect us from burn wounds. The skin's sensation can protect us from first and second degree burns, but in cases of third degree burns it is less effective, as we don’t feel any pain due to the fact that the nerve endings in the skin are destroyed (which indicates a more severe injury).
- Endocrine function: Skin is one of our main sources of vitamin D, through the production of Cholecalciferol (D3) in the two lowermost layers of the epidermis (the stratum basale and stratum spinosum).
When to See a Doctor
Being the first line of defense against the outside world, you should see your doctor when you have one or more of the following signs and symptoms:
- Signs of inflammation (redness, heat, swelling, pain and fever)
- Signs of infection (pus, fever, swelling and pain)
- Allergic reaction (itching, redness, hives or skin rash, and heat)
- Abnormal skin moles (irregular shape, large, painful or itching)
- New nodules, lumps or skin discoloration
How to Protect Your Skin
- Avoid excessive exposure to sunlight (use sunscreens, sunblocks and protective clothes)
- Regular cleaning with soap and water
- Regular checks of moles, skin creases, sweaty areas (between toes, armpits or groin area)
- Apply topical over-the-counter moisturizers (to prevent dryness and cracks)
- Avoid walking bare footed