The Science of Skin Hydration — Beyond Moisturisers

Last updated: 5 March 2026

Why Skin Hydration Is More Complex Than You Think

Skin hydration is a concept that most people associate simply with applying moisturiser. However, the science of how skin maintains its moisture balance is remarkably complex, involving multiple structural components, active biological processes, and environmental interactions. Understanding these mechanisms is essential for both effective skincare and optimising aesthetic treatment outcomes.

At Axiom Aesthetics, we take a scientific approach to skin hydration, combining advanced in-clinic treatments with evidence-based homecare recommendations to address hydration at every level.

The Skin Barrier: Your Built-In Hydration System

The stratum corneum — the outermost layer of the epidermis — functions as the primary barrier against water loss. This brick and mortar structure consists of:

• Corneocytes (bricks) — flattened, dead skin cells filled with keratin and natural moisturising factors (NMFs)
• Intercellular lipids (mortar) — a complex mixture of ceramides (50%), cholesterol (25%), and free fatty acids (25%) that fills the spaces between corneocytes
• Natural Moisturising Factors (NMFs) — hygroscopic (water-attracting) substances within corneocytes, including amino acids, urea, lactic acid, pyrrolidone carboxylic acid (PCA), and minerals

Transepidermal Water Loss (TEWL)

TEWL is the passive evaporation of water through the epidermis to the external environment. A healthy skin barrier maintains TEWL within normal limits (typically 5-10 g/m²/hour on the face). Elevated TEWL indicates barrier dysfunction and is associated with:

• Dry, flaky, rough skin texture
• Increased sensitivity and irritation
• Impaired wound healing
• Increased susceptibility to infection
• Accelerated skin ageing

The Role of Hyaluronic Acid in Skin Hydration

Hyaluronic acid (HA) is the most famous hydrating molecule in skincare and aesthetics, and for good reason. This glycosaminoglycan has a remarkable capacity to hold water — one gram of HA can bind up to 6 litres of water. In the skin:

• Dermal HA — approximately 50% of the bodys total HA resides in the skin, primarily in the dermis where it maintains tissue hydration and creates the gel-like matrix between collagen and elastin fibres
• Epidermal HA — present in smaller quantities in the epidermis, contributing to barrier function and wound healing
• Age-related decline — HA content decreases significantly with age, contributing to loss of skin plumpness, hydration, and elasticity

Topical HA: Size Matters

• High molecular weight HA (>1000 kDa) — sits on the skin surface, forming a hydrating film. Does not penetrate the stratum corneum
• Medium molecular weight HA (100-1000 kDa) — limited penetration into the upper epidermis
• Low molecular weight HA (10-100 kDa) — penetrates deeper into the epidermis
• Nano/ultra-low molecular weight HA (<10 kDa) — deepest penetration, may stimulate HA production in the skin
• Multi-weight formulations — the most effective topical HA products combine multiple molecular weights for hydration at every level

In-Clinic Hydration Treatments

Skin Boosters

Injectable HA skin boosters deliver hyaluronic acid directly into the dermis:

• Profhilo — a unique formulation of high and low molecular weight HA that spreads beneath the skin, providing deep hydration and stimulating collagen and elastin production. Five injection points per side of the face (BAP technique)
• Restylane Skinboosters (Vital/Vital Light) — micro-droplets of stabilised HA injected into the dermis, improving hydration, smoothness, and elasticity. Course of 3 sessions recommended
• Juvederm Volite — injectable HA designed to improve skin quality and hydration for up to 9 months with a single treatment

Polynucleotide Therapy

Polynucleotides improve skin hydration by stimulating fibroblast activity and promoting the production of endogenous HA and collagen within the skin.

Mesotherapy

Micro-injections of customised cocktails containing HA, vitamins, minerals, amino acids, and peptides deliver hydration and nutrients directly to the dermis.

Microneedling with HA

Creating micro-channels with a microneedling device followed by application of HA serum allows deeper penetration of the hydrating molecules into the skin.

Hydrating Ingredients in Skincare

Beyond HA, several ingredients contribute to skin hydration through different mechanisms:

Humectants (Draw Water In)

• Glycerine — one of the most effective and well-studied humectants
• Urea (5-10%) — a natural NMF component with both humectant and mild exfoliating properties
• Panthenol (provitamin B5) — hydrating, soothing, and barrier-supporting
• Alpha-hydroxy acids (at low %) — lactic acid and glycolic acid have humectant properties at low concentrations

Emollients (Smooth and Soften)

• Squalane — mimics skins natural sebum; lightweight and non-comedogenic
• Fatty alcohols — cetyl, cetearyl, and stearyl alcohol smooth and soften
• Natural oils — jojoba, rosehip, and argan oil (used as part of a balanced routine)

Occlusives (Seal Moisture In)

• Ceramides — the most important barrier lipids; restore and reinforce the intercellular lipid matrix
• Petrolatum — the most effective occlusive, reducing TEWL by up to 98%
• Shea butter — rich in fatty acids with excellent occlusive properties
• Dimethicone — silicone-based occlusive that is cosmetically elegant and non-comedogenic

Factors That Compromise Skin Hydration

• Over-cleansing — stripping the skin of its natural oils and NMFs
• Over-exfoliation — excessive use of AHAs, BHAs, or physical exfoliants damages the barrier
• Environmental factors — central heating, air conditioning, cold weather, wind
• Retinoid overuse — retinoids can impair barrier function if not introduced gradually
• Hot water — washing with very hot water strips lipids from the skin surface
• Alcohol-based products — drying alcohols (denatured alcohol, SD alcohol) in skincare products
• Inadequate water intake — while topical hydration is more important for skin, systemic dehydration affects skin turgor and health

“Hydrated skin is healthy skin. Every aspect of skin function — from barrier integrity to wound healing to the efficacy of aesthetic treatments — is optimised when the skin is properly hydrated.” — International Journal of Dermatology

Frequently Asked Questions

Summary

True skin hydration goes far beyond simply applying moisturiser. It involves maintaining a healthy skin barrier, replenishing natural moisturising factors, and addressing hydration at both the surface and deeper dermal levels. At Axiom Aesthetics, we combine in-clinic treatments such as skin boosters and mesotherapy with personalised skincare recommendations to optimise skin hydration — the foundation upon which all other aesthetic improvements are built.