Free Water Content in the Skin: What It Is and How to Optimise It

Hydration is often reduced to marketing buzzwords and topical solutions, but from a corneotherapeutic standpoint, it involves far more than applying a moisturiser. To maintain optimal skin function, we must understand and support free water content in the stratum corneum.

What is Free Water Content?

In skin physiology, water exists in two forms:

• Bound water, which is tightly associated with molecules such as proteins (e.g. keratin) and natural moisturising factors (NMFs)

• Free water, which exists in the intercellular spaces and is not chemically bound

  
  

Free water resides predominantly within the intercellular lipid matrix of the stratum corneum, where it contributes to the skin's mechanical properties, enzymatic activity, and barrier function.

It is essential for:

• Enzymatic desquamation: The breakdown of corneodesmosomes requires sufficient water for the enzymes to function effectively.

• Barrier homeostasis: Water supports the lamellar structure of intercellular lipids and facilitates their repair mechanisms.

• Plasticity and flexibility: Adequate free water helps maintain the skin’s biomechanical properties, preventing fissures, cracking, and microinflammation.

  
  

When free water levels decline, often due to a disrupted barrier, environmental exposure, or incorrect skincare, the skin exhibits dryness, roughness, impaired desquamation, and increased TEWL (trans-epidermal water loss).

How to Improve Free Water Content: A Corneotherapeutic Approach

Rather than simply replacing lost water, the focus is on restoring the skin’s ability to retain water, with strategies focused on barrier repair and physiological function.

1. Reinforce the Intercellular Lipid Matrix

The stratum corneum's barrier function depends on the integrity of its lipid bilayers, primarily composed of ceramides, cholesterol, and free fatty acids in a specific ratio (approximately 3:1:1). Replenishing these lipids with biomimetic formulations supports lamellar bilayer formation, reducing TEWL and increasing the skin’s capacity to hold free water.

2. Support NMF Synthesis

The natural moisturising factor (NMF) is a complex mixture of low molecular weight, water-soluble compounds (including urea, lactic acid, PCA, and amino acids) derived from the breakdown of filaggrin in terminally differentiating keratinocytes. NMF binds water within corneocytes, helping regulate water activity in the stratum corneum.

Therapeutically, the goal is to:

• Avoid disrupting filaggrin synthesis through excessive exfoliation or barrier damage

• Restore NMF components topically (e.g. through urea or lactate))

  
  

3. Incorporate Physiological Humectants

Humectants such as glycerol, sodium lactate, and hyaluronic acid attract water into the stratum corneum from the dermis or external environment. However, their use must be supported by a competent barrier, otherwise, the water they attract can be lost through evaporation, leading to net dehydration. Corneotherapy emphasises pairing humectants with lamellar lipid structures to ensure retention.

4. Mitigate TEWL

To sustain water levels, TEWL must be minimised. TEWL is a passive process where water escapes through the epidermis to the atmosphere, and its rate increases significantly when the barrier is compromised. Non-occlusive lipid-based formulations containing squalane, phospholipids, or skin-identical lipids form a breathable protective layer that preserves hydration while supporting barrier repair. Unlike heavy occlusives (e.g. petrolatum), these do not inhibit normal barrier function or interfere with corneocyte maturation.

5. Account for Environmental and Behavioural Stressors

Free water levels are influenced by external and internal factors:

• Low ambient humidity and UV radiation increase TEWL

• Over-cleansing, particularly with alkaline or surfactant-heavy products, disrupts corneocyte cohesion and barrier lipids

• Prolonged water exposure (especially hot water) extracts NMF and disrupts lipid bilayers

Reducing these exposures is as important as product choice. Seasonal skincare adjustments and using humidifiers in dry environments can help maintain cutaneous hydration.

6. Optimise Internal Hydration and Lipid Intake

Systemic hydration affects the water gradient across the epidermis, and nutritional support, particularly essential fatty acids (omega-3 and omega-6). These contribute to barrier lipid synthesis. A deficiency in linoleic acid, for instance, is associated with increased TEWL and barrier dysfunction.

Summary

It must be remembered that improving free water content is not about forcing moisture into the skin, rather it’s about preserving the skin’s innate ability to regulate and retain it. In corneotherapy, this means:

• Restoring physiological lipids

• Supporting NMF production

• Avoiding barrier-disrupting practices

• Using biomimetic, skin-identical formulations

• Respecting the skin’s structure, lifecycle, and environment

 Maria Rylott-Byrd aka The Corneotherapy Consultant™ is the creator of Epidermal Skin Health – A Corneotherapist’s Essential Guide, a comprehensive skin science-led course designed to deepen understanding and elevate professional expertise.

visit www.thecorneotherapyconsultant.co.uk to learn more