Transepidermal Water Loss: Science & Skin Barrier
What Is TEWL?
Transepidermal water loss measures passive water diffusion through the epidermis. Normal: 5-15 g/m2/h. Above 20 indicates barrier dysfunction. Above 30 suggests significant damage.
Why TEWL Matters
Elevated TEWL is the earliest sign of barrier damage, appearing before visible dryness. Subjects with TEWL above 15 were 3x more likely to develop sensitivity to previously tolerated products.
Signs of Elevated TEWL
- Skin feels tight 10-15 minutes after cleansing
- Products sting that did not before
- Fine lines more pronounced in morning
- Skin looks dull and slightly translucent
- Makeup settles into patches within hours
What Damages Your Barrier
Over-exfoliation (most common), hot water cleansing, retinoid overuse, alkaline soaps (pH above 7), environmental dryness below 30% humidity, stress-induced cortisol.
How to Reduce TEWL
Immediate (24-48 hours)
Petrolatum-based occlusive at night reduces TEWL by 98%. Vaseline or Aquaphor on damp skin.
Short-term (1-2 weeks)
Ceramide moisturizers. Humidifier at 40-50%. pH 5.0-5.5 cleanser.
Long-term (4-8 weeks)
Niacinamide 5% increases ceramide synthesis. Gradually reintroduce actives starting with lower concentrations.
