To understand what Transepidermal Water Loss really means, we need to have some knowledge of the skin’s main functions. The skin's primary functions are to serve as a barrier to the entry of microbes and viruses, and to prevent water and extracellular fluid loss. Acidic secretions from the skins glands also retard the growth of fungi. Melanocytes form a second barrier: protection from the damaging effects of ultraviolet radiation. When a microbe penetrates the skin (or when the skin is broken by a cut) the inflammatory response occurs.
The Skin is divided into three layers
- The Epidermis outer and top layer.
- The Dermis deeper layer.
- The Hypodermis subcutaneous tissues.
THE SKIN FORMS THREE TYPES OF BARRIERS
1. Chemical Barrier - Includes skin secretions and melanin. The skins surface is covered with bacteria (skin microbiome) the low pH of skin secretions known as the Acid Mantle decreases their multiplication. Many bacteria are killed by anti-bacterial substances in the sebum. Skin cells also secrete a natural anti-biotic known as 'human defensin'. Melanin provides a chemical pigment shield to prevent UV damage to the viable skin cells. Keratin - is a protein found in skin, hair and nails; it prevents both the loss of body fluid through the skin and entry or excessive water into the body.
2. Physical Barrier - Is offered by the continuity of the skin and the hardness of it's keratinised cells. The waterproofing of the glycolipids of water soluble subances between cells preventing both water loss from and entry into the body through the skin. Substances that do penetrate the skin in limited amounts (here are some examples):
- Lipid soluble substances such as oxygen, carbon dioxide, fat soluble Vitamins A // D // E // K, steriods and some bio-active botanical extracts.
- Oleoresins of certain plants (poison Ivy).
- Organic Solvents such as acetone, dry cleaning fluid, paint thinner (these dissolve the cells lipids).
3. Biological Barriers - Langerhans cells in the epidermis and macrophages in the dermis. Langerhans cells - are active elements of the immune system which protect the Dermis against foreign substances (antigens). Macrophages - are the second line of defence and kill viruses and bacteria that have managed to penetrate the Epidermis.
An aqueous film covers the Epidermis is is known as the Acid Mantle read 'The Skin's Acid Mantle'. It comprises of the:
- Secretions from tour sweat and sebaceous glands.
- Peptides derived from the breakdown of our dead skin cells known as corneocytes.
- Epidermal lipids provide a protective film comprised of sebum and the epidermal lipids (upper film); underneath (lower film) is the natural moisturising factor (NMF), which is comprised of water based molecules present on the epidermal surface (the top layer of your skin.
- Up to 15% of the Stratum Corneum (outermost layer of the skin) consists of water. When this drops to below 10% your skin starts to feel dry and flaky. As we age the skin naturally become drier.
What is Transepidermal Water Loss
The Skin is not a completely impermeable barrier, a certain amount of water continuously diffuses into the environment. This is the process known as Transepidermal Water Loss (TEWL). It is defined as "passive water loss through an intact stratum corneum" (excluding active perspiration through sweat glands and hair follicles) Increased TEWL is due to an impaired barrier function usually related to the hydration of the stratum corneum. These two parameters are used for the assessment of the skins' barrier function and it's a general condition (health).
The optimal water content of a healthy stratum corneum is 13-20%, preventing excessive TEWL is achieved by maintaining proper hydration of the skin.
ENVIRONMENTAL AGGRESSORS // Wind, cold, and humidity cause dehydration, symptoms of an impaired skin barrier include:
- Flaking // A typical sign of dehydrated skin.
- Tightness // Is often associated with a dry skin.
- Redness // Due to the barrier being unable to protect against irritants causing Inflammation.
- Itchiness // The damaged barrier can affect nerve endings which leads to itching, when the skin is scratched to relieve the itching, the barrier function is injured causing inflammation and redness.
How can you prevent Transepidermal Water Loss?
Topical Application of Fatty Acids can have a number of positive effects on the skin, the most important being, boosting lipid content and the repair of the skin's barrier function. This helps protect delicate skin, improves moisture levels, helps the skin retain it’s own moisture which all leads to improved softness and elasticity. Omegas are particularly beneficial to dry skin, conditions such as eczema and during extreme weather conditions, such as cold and wind, both of which can strip away at the skin's protective lipid barrier.
Omegas 3 + 6 are building blocks of healthy cell membranes. These are polyunsaturated fats and help the skins natural oil barrier - this is critical in keeping the skin hydrated, ‘plump’ and preventing water loss.
OCCLUSIVES // Create a thin film over the skin, helping to create a barrier against water loss, preventing the skin from losing moisture. They don’t increase the moisture levels of the skin but can help prevent water reserves from being drained by external stressors.
- Avocado Oil // Prevents the evaporation of the water from the skins surface, contains Lecithins which help to prevent moisture loss.
- Beeswax // Provides a physical barrier, sealing moisture into the tissues whilst preventing water loss.
- Jojoba Oil // Technically although resembling an oil it is in fact a wax. It provides a light film on the skin that maintains and attracts moisture.
- Shea Butter // Fatty substance obtained from the nuts of the shea tree from West Africa, is extremely moisturising and very hydrating, when applied to the skin, it provides immediate softness and smoothness.
- Squalene // Oil high in Squalene - Olive Oil // Wheat Germ oil // Rice Bran Oil // Argan Oil // Camellia Oil // Macadamia Oil.
HUMECTANTS // Are water-rich, they mimic the skin’s sweat and work by hydrating the skin. They have been specifically designed to prevent water loss, and protect the stratum corneum, the outer layer of skin from becoming dry and parched. Some humectants are capable of holding up to 1000 times their own weight in water, acting as moisturizers for the skin:
- Aloe // Penetrates skin deeply and quickly, hydrating at the surface and at the lower levels. Due to its gentle properties, aloe is great for hydrating dry skin that is also sensitive.
- Honey // With the ability to hold onto water, hydrating without creating an oily feel. It’s also a natural source of alpha hydroxy acids, which encourage exfoliation. This makes it even easier for skin to absorb the moisturising elements.
- Hyaluronic Acid // A natural molecule present throughout the body that helps hydrate and cushion joints, eyeballs, and skin. It has a natural ability to hold onto water, and seems able to adjust according to humidity levels, helping your skin cope with even dry climates. Antioxidant properties and an impressive ability to hold up to 1000 times its weight in water makes this a popular addition to many skincare products.
- Glycerin [Vegetable] // It occurs naturally in every living cell so it's easily absorbed by the skin. It holds water really well and it works by finding an equilibrium between the water content in the air and in the skin. Along with the benefits of deep hydration, the texture of glycerin makes it perfect for skin care because it glides on smoothly and evenly. It is derived from plant-based oils, and helps keep the skin soft, as it continues to work even after it has been rinsed off. Glycerol is colorless, odorless and very gentle on the skin, making it safe for sensitive skin.
- Lecithin // [from soya beans or sunflower] Hydrophilic ingredient - It attracts water to the skin, working to prevent moisture loss from deep within the skin tissues.
- Seaweed + Algae // Creating a moist film over the surface of the skin, helping to retain water in the skins upper layers.
Steps you can take to maintain hydrated skin //
- Apply a topical face oil // serum // moisturiser to protect from transepidermal water loss.
- Avoid exposure to dry air.
- Avoid prolonged contact with hot or chlorinated water.
- Use a gentle Cleansing Oil instead of soap.
- Avoid using skin care products that contain alcohol.
- Moisturise immediately after a bath, shower or washing your hands and regularly throughout the day, adding moisture to the skin helps to normalised cell turnover and strengthen the skins barrier function.
- Use a humidifier.
- Wear a scarf and gloves when going out in cold weather.
Until next time..
be human, be kind, be you.
BOOK: Modern Cosmetics - Ingredients of natural Origin A scientific Review Volume 1 - Dr D Janes & Dr N K Glavac.
Formular Botanica: Skin Anatomy & Physiology, Diploma in Organic Skincare Formulation.