This is the third week of ‘Skin Facts’ and last week, we’ve looked into the sun protection function of children vs adult skin, and how the sun affects eczema skin. Today, we’re looking into another critical function of skin and one that is very relevant for eczema skin – our skin’s moisture retention property. One can also view it as how much moisture is lost from our skin, known as Transepidermal Water Loss (TEWL). TEWL is studied by dermatologists, as excessive TEWL points to a defective skin barrier, and in severe cases, affect the ability of the body to function. Let’s go “water deep” into this skin function!
Water and our Body
Water makes up a large point of our body weight, here are some interesting facts about the water in our body from water.USGS.gov (the US Geological Survey website):
Water content in our Body
- Lungs 83%
- Muscle 79%
- Kidneys 79%
- Brain 73%
- Heart 73%
- Liver 71%
- Skin 64%
- Bones 31%
Percentage of Body Weight that is Water
- Fetus 94%
- Infant at birth 78%
- One-year old 65%
- Female 55% (due to higher fat content)
- Male 60%
- Elderly 50%
Functions of Water in our Body
- Forms the building material of cell
- Regulates body temperature by sweating and respiration
- Transport via the bloodstream
- Flushes waste via urination
- Absorbs shock for brain and spinal cord, also lubricates joints
- Forms saliva
Water Loss from our Skin
Our skin allows water to be lost through it, as part of insensible perspiration (or transepidermal diffusion) and sweating. Insensible refers to us not being aware of it (another insensible loss of water is from respiration). Sweating helps regulate our body temperature, via cooling of the skin. However, sufficient intake of water is required in order for sweating to not dehydrate the body and continue to be effective in cooling our body temperature.
Much of the water is lost through the stratum corneum, the upper most layer of the epidermis made up of a dead cell layer. A defective stratum corneum layer will allow excessive epidermal water loss and potentially, increase risk of irritant and allergen sensitivity. Water loss from evaporation from our skin is about 400ml daily in an adult. For research news on how the skin can be a channel for allergy, see Food Sensitization from Eczema.
Transepidermal Water Loss (TEWL) from Children Skin
TEWL from baby skin is higher than normal adult skin, due to their thinner stratum corneum. For premature infants less than 30 weeks, there are also fewer layers of stratum corneum resulting in increase fluid and heat loss. Interestingly, infant skin is found to have higher water content and able to absorb more water but lose excess water faster than adult skin. TEWL was also strongly predictive of AD at 12 months (study here). The natural moisturizing factor (protein breakdown products such as small amino acids, urea, pyrrolidone carboxylic acid, ornithine, citrulline, urocanic acid) in infant is also lower than an adult.
How this Impact Parents Caring for Baby Skin
Protection of the stratum corneum is important, and this can be via:
Reduced bathing – Washing baby skin with a washcloth during the first 4 weeks of life is associated with increased TEWL and decreased stratum corneum hydration compared with simply soaking in water. The recommendation is to use a mild liquid cleanser with water (less drying than water alone), and that bathing should be brief (10 minutes or less) and no more than every other day with spot cleaning in between.
Good bathing regimen – Includes not using hot water, not scrubbing the skin dry (but pat dry), keeping it short to 10 minutes, not using soap and moisturizing right after (see video)
Good skincare regimen – Moisturizing protects the skin barrier (see video). It is important to note that given the thinner stratum corneum of infants, their higher surface area to body ratio, infants are more vulnerable to toxicity of products. Therefore, be sure you understand the product label (there’s a comprehensive Sensitive Skin Products blog series to help you with that).
Transepidermal Water Loss (TEWL) from Eczema Skin
TEWL is studied to be higher in eczema skin and also dry skin (without eczema). The water content of stratum corneum is also lower in adults with eczema than normal skin. It is also studied at the natural moisturizing factor of eczema skin is defective, lacking in proteins that are able to play a role in the skin’s humectant property – the ability to pull moisture from the environment and retain this water (which is why 2nd generation moisturizers incorporated humectant property, learn more here).
Drinking Water and Skin
A myth. Dehydration will affect skin but drinking excess water will not lead to ‘glowing’ skin. Drinking enough water will also not prevent skin aging or wrinkles as these are related to genetics, sun and oxidative stress brought on by pollutants. Read this #SkinishMom Investigation! – Drinking water for dry skin
To round-up, we learnt that water is integral to our body and to our skin. We have insensible water loss and a thinner stratum corneum in baby skin and a defective stratum corneum in eczema skin both results in increased transepidermal water loss (TEWL). This knowledge should encourage (not discourage!) us to be more committed to a good bath and skincare routine.
What’s your take in this?
- USGS Water Science School – The Water in You
- Project Wet – Hydration
- Acta Derm Venereol 2000; 80: 188±191 – CLINICAL REPORT – Skin Surface pH, Stratum Corneum Hydration, Trans-epidermal Water Loss and Skin Roughness Related to Atopic Eczema and Skin Dryness in a Population of Primary School Children
- Nutr Rev. 2010 Aug; 68(8): 439–458. Water, hydration and health
- Insensible Water Loss
- The Journal of Allergy and Clinical Immunology – Skin barrier dysfunction measured by transepidermal water loss at 2 days and 2 months predates and predicts atopic dermatitis at 1 year
- Cosmetics & Toiletries – Baby Skin vs. Adult Skin Structure, Function and Composition