TEWL (Transepidermal Water Loss)
TEWL (Transepidermal Water Loss) — the process by which water evaporates from inside the body outward through the skin and into the environment. A certain baseline amount is normal, but an elevated rate can signal a compromised skin barrier that struggles to hold onto moisture.
Key points
- TEWL measures how much water passes through the epidermis and evaporates from the skin's surface.
- A low, stable TEWL rate generally reflects a healthy, intact barrier, while a high rate can indicate barrier damage.
- Factors such as harsh cleansing, low humidity, over-exfoliation, and certain skin conditions can increase TEWL.
- Occlusive and humectant ingredients are commonly used to help reduce excessive water loss and support hydration.
Frequently asked
Is transepidermal water loss always bad?
No, a small amount of TEWL is a normal part of healthy skin function. It becomes a concern only when the rate is elevated, which can point to a weakened barrier.
How can I lower high TEWL?
Supporting the barrier with gentle cleansing and moisturizers containing humectants, emollients, and occlusives can help reduce excessive water loss. Avoiding over-exfoliation and harsh products also helps.
Related topics
This is a foundational entry in the SYNC Skin Encyclopedia and is expanded over time. Educational information only — not medical advice.
