Your Skin’s Gatekeeper
The epidermis is the skin’s outer structure, the part of our skin that we see in the mirror each day. It is the horny layer that is the end result of a 4-to-6-week process called keratinization. Keratinization is the process where cells are born in the lowest part of the epidermis, called the basal layer, and then undergo many changes as they migrate to the surface to be shed.
During the process of keratinization, cells become filled with a hardened protein called keratin. As the flattened, hardened keratin-filled cells are sloughed off (desquamation), new skin cells are born in the basal layer. When we turn over in our beds, take a shower, get dressed or do anything that creates friction we shed skin cells. We can shed up to nine pounds of skin cells yearly!
One of the major functions of the epidermis is to prevent water loss from our skin. The epidermis produces lipids, which consist of ceramides, cholesterol and fatty acids. They act as the cement between the bricks of keratin-filled cell layers. The combination of the two forms a waterproof barrier which minimizes trans-epidermal water loss (TEWL). The epidermis is sometimes referred to as the moisture barrier.
The epidermis protects us from outside invaders like bacteria, chemicals and other allergens and pathogens. One of nature’s small miracles is giving this outer layer a slightly acidic pH (4.5 to 6.5). These slightly acidic layers of the moisture barrier are called the acid mantle. The acidity comes from a combination of secretions from sweat and oil producing glands. Because the mantle is acidic, it inhibits the growth of fungi and bacteria within the skin. Another benefit of this acidity is that it helps to maintain the hardness of the keratin-filled cells. When the skin’s surface becomes alkaline, the hardened cells become loose and soft, causing the skin to lose some of its protective properties. Using harsh soaps and detergents can make the skin more alkaline which makes it more prone to infection. It may also make the skin feel rough and dehydrate it.
Like an army continuously protecting us from the outside world, your epidermis contains highly specific cells that are each designed with specific duties. Melanocytes are cells found in the deepest layer of the epidermis which produce a substance called melanin. Melanin is the pigment which gives your skin its color and helps to protect you from the harmful effects of the sun. When you get a tan, melanin is what makes your skin appear “tan” or freckled.
Think of your epidermis as your skin’s gatekeeper. It keeps the bad stuff out and the good stuff in. Most products—including moisturizers—are unable to make it past the epidermis to where aging happens.