Transepidermal Water Loss (TEWL)
Transepidermal Water Loss (TEWL) refers to the amount of water that passively evaporates from the deeper layers of the skin through the epidermis and into the surrounding environment. It is a natural physiological process, but when TEWL levels are elevated, it typically indicates a compromised skin barrier and impaired hydration.
TEWL is a key marker in dermatology and cosmetic science for assessing skin barrier function, hydration status, and product effectiveness. It is often used to evaluate the impact of moisturisers, barrier-repair treatments, and environmental stressors on skin health.
What Increases TEWL?
- Damage to the stratum corneum from over-exfoliation, harsh cleansers, or irritants.
- Skin conditions like eczema, psoriasis, or atopic dermatitis.
- Low humidity environments, wind, or cold weather.
- UV exposure and pollution.
- Age-related thinning of the skin’s outer barrier.
Why TEWL Matters in Skincare
- Increased TEWL leads to dehydration, flakiness, and sensitivity.
- Chronic barrier dysfunction can contribute to inflammation and skin disorders.
- TEWL reduction is a primary goal of barrier-repair moisturisers and occlusive agents.
- Used in clinical and cosmetic testing to measure the efficacy of skincare formulations.
How to Reduce TEWL
- Use humectants like glycerin or hyaluronic acid to attract moisture.
- Apply emollients and occlusives (e.g., ceramides, petrolatum) to seal in hydration.
- Strengthen the lipid barrier with ingredients like niacinamide, squalane, and fatty acids.
- Avoid over-cleansing and harsh exfoliants that strip the skin.
- Protect skin from environmental aggressors (UV, pollution, cold air).
Conclusion
TEWL is a vital concept in understanding skin health and hydration. While some water loss is normal, excessive TEWL is a sign of a damaged or weakened skin barrier and often correlates with dryness, irritation, and sensitivity. Effective skincare formulations aim to reduce TEWL by reinforcing the skin’s natural defences and maintaining optimal moisture levels.