Transepidermal water loss, or TEWL, is an essential concept to understand when considering skin dryness. Although often overlooked, TEWL is one of the main reasons why moisturizing the skin regularly and with the right products is a crucial step in keeping skin healthy and hydrated.
WHAT IS TRANSEPIDERMAL WATER LOSS?
TEWL occurs when the outermost layer of our skin, the epidermis, loses water to the surrounding air through evaporation. In fact, each day, the skin loses approximately one pint of water through TEWL. In a fairly humid environment, water evaporation from the skin is slow, and the body can readily replenish the water lost to the air. However, when water evaporates faster than the body can replace it, the skin becomes dehydrated, which can lead to irritated, rough and/or itchy skin that can crack and cause discomfort. Dry skin also tends to appear more aged, as fine lines and wrinkles are accentuated.
BALANCING SKIN MOISTURE LEVELS
Optimizing the skin's moisture level is key to skin health and an important element in ensuring a youthful appearance. To achieve proper skin hydration and treat dry skin, internal and external factors must be considered.
We all know that meeting our water intake goals each day is beneficial to the body. Water aids in digestion, regulation of body temperature, transportation of nutrients and much more. And while a jury has long been out regarding its ability to directly benefit the skin, recent studies like this one have demonstrated that regular consumption of water does indeed lead to improvement in skin hydration. That's the internal side of the equation.
Ensuring that our skin is hydrated, however, doesn't prevent TEWL. If anything, the more water content in the skin, the greater the opportunity for TEWL to occur. Rather, from an external perspective, we must focus on slowing the rate of TEWL. To do that, we look to moisturizers.
There are three main categories of ingredients found in an effective moisturizer – humectants, occlusives and emollients. Humectants, such as propylene glycol, hyaluronic acid and sorbitol, are substances that naturally attract water. When used in humid conditions, humectants pull water from the environment to the skin. In dry environments, humectants often draw moisture from the deeper layer of skin – the dermis – to the epidermis. After humectants hydrate the skin, the water could easily evaporate. This is where occlusives come in. Occlusives, like petrolatum, caprylic/capric triglyceride and beeswax, are hydrophobic substances that act as a barrier through which water cannot pass. (With certain occlusives on the skin, the rate of TEWL can decrease by up to 98%!) Finally, emollients, including isopropyl palmitate, dimethicone and jojoba seed oil, are substances that help keep the skin smooth, flexible and lubricated. Many emollient constituents found naturally in the skin's oils, such as lipids and fatty acids, play important roles in the skin's architecture. In moisturizers, they improve the feel and comfort of the skin while greatly reducing TEWL.
ADDITIONAL TIPS TO SLOW TRANSEPIDERMAL WATER LOSS
TEWL is accelerated when the skin's barrier function is disrupted. Therefore, the amount of water that comes into contact with the skin should be limited. Water dilutes and washes away skin oils that act as natural occlusives to keep water in the epidermis. High water temperature can also increase TEWL, as it opens the skin's pores, allowing more moisture to evaporate. Shorter, cooler showers and baths are recommended for optimal skin health.
Avoid strong soaps. Heavy-duty soaps and cleansers with high pH levels can rapidly diminish the skin's supply of natural oils leaving moisture in the epidermis free to evaporate. Rather, turn to gentle cleansers or glycerin bars.
In dry climates or during dry seasons, use a humidifier in your home or office. TEWL is slower in humid environments.
Reapply lotions and moisturizers regularly to ensure that skin stays protected. This is especially important after washing hands or cleansing the face or body.