Health & Longevity Series · Medical education

The skin barrier

Epidermal barrier function and transepidermal water loss

3 min read

01Overview

How the skin barrier works

Key takeaway for patientsA sound barrier keeps water in and irritants out. Dry, reactive skin usually signals a barrier under strain, and persistent problems such as eczema can be assessed and managed.

The barrier lives in the stratum corneum, the outermost layer of the epidermis. It is often described as bricks and mortar: flattened cells (corneocytes) are the bricks, and a lipid matrix of ceramides, cholesterol and fatty acids is the mortar.

The barrier keeps water in and keeps irritants, allergens and microbes out. A slightly acidic surface and the protein filaggrin, which breaks down into natural moisturizing factors, help to maintain it. When the barrier is impaired, water loss rises and the skin becomes dry, reactive and prone to inflammation.

02Key steps

Key steps in building the barrier

Cornification: Keratinocytes flatten and harden into corneocytes.
Lipid secretion: Ceramides, cholesterol and fatty acids fill the spaces between them.
Natural moisturizing factors: Filaggrin breaks down into molecules that hold water.
The acid mantle: A low surface pH supports the skin’s enzymes and resident microbes.

03Factors in decline

Factors that impair the barrier

The barrier is worn down from outside and weakened from within:

Over-washing and harsh cleansers: Strip the lipid matrix.
Low humidity and cold: Increase water loss.
Genetic factors: Variants of filaggrin are linked with eczema.
Aging: Lipid production falls.

04Clinical management

Clinical management and physician guidance

Persistent dryness or irritation is assessed as a skin condition.

Skin assessment: Examination and history, including the products in use.
Physician-guided care: Gentle skin care and the care of any skin condition, as your physician decides.
Monitoring and follow-up: Symptoms and markers are reviewed over time, and the plan is adjusted to them.

05Research focus

Research focus in barrier biology

Core focus area	Biological target	Clinical relevance
Barrier lipids	Ceramides	Retention of water
Structural proteins	Filaggrin	Natural moisturizing factors and the risk of eczema
Barrier measurement	Transepidermal water loss	How barrier function is assessed
Surface ecology	Skin pH and the microbiome	Defense against pathogens

06Questions

Frequently asked questions

What does a damaged barrier feel like?: Dry, tight, stinging or easily irritated skin.
Can washing damage the barrier?: Frequent washing with harsh cleansers removes the lipids that hold it together.
When should I see a physician?: For persistent dryness, itching or rashes, which may be eczema or another skin condition.

07References

Academic references and literature

Elias PM (2008). Skin barrier function. Curr Allergy Asthma Rep, 8(4), 299-305. PMID 18606081.
Palmer CN et al. (2006). Common loss-of-function variants of the epidermal barrier protein filaggrin are a major predisposing factor for atopic dermatitis. Nat Genet, 38(4), 441-6. PMID 16550169.
Proksch E, Brandner JM, Jensen JM (2008). The skin: an indispensable barrier. Exp Dermatol, 17(12), 1063-72. PMID 19043850.

This guide belongs to the Skin Health program