Moisturiser Chemistry Explained

Florence Barrett-Hill
What does a moisturiser do?

There is a common misconception that moisturisers are defined as chemicals that increase the water content of the stratum corneum and are hydrating agents. This misconception leads one to believe that the water content of the moisturiser has the greatest effect on the skin. But like many things in aesthetics & beauty therapy, it is only part of the story……

When the skin is damaged repair is dependent on retarding the loss of moisture from the skin, not just putting more moisture into the skin. This is done by concentrating on the repair or temporary replacement of skin barrier defence systems like the acid mantle.

  • Moisturisers work by using ingredients that are occlusive and/or humectant agents.
  • These ingredients are the same or similar to natural components in the skin (biomimetic).

Occlusive agents work by physically blocking the loss of water from the skin.

  • These hydrophobic agents form an occlusive film on the skin that reduces TEWL by preventing evaporation of water from the stratum corneum.
  • These agents may also help to restore the lipid barrier of the skin.
  • Examples of occlusive agents include petrolatum, beeswax, lanolins and oils.

Humectant agents attract water to the skin.

  • The water is drawn from the deeper dermis, rarely the environment and is carried to the dermis via the lymphatic system.
  • The hydration of the stratum corneum normalises the intercellular lipids and the natural desquamation process.
  • The skin becomes more resistant to drying conditions
  • Humectants mimic the role of natural hydrophilic humectants in the stratum corneum.
  • These chemicals include amino acids, lactic acids, alpha hydroxy acids, propylene glycol, glycerine and urea.
  • Some of these agents are the components of the skin’s natural moisturising factors.

“Barrier-repairing” moisturisers contain lipids that are similar to the intercellular lipids of the skin. The combinations of fatty acids, ceramide and cholesterol in the moisturisers may help to repair lipid bilayers affected by soaps, solvents and extremely dry, cold weather conditions by replacing key lipid components.

Moisturisers contain other ingredients besides humectants and/or occlusive agents.

  • Ingredients may improve the skin’s softness by lubricating and filling in the spaces between dry skin cells. An ingredient list on a moisturiser will list these agents as the “active” ingredients.
  • The “inactive” ingredient solubilise, stabilise, emulsify, suspend and /or disperse ingredients in order to produce an aesthetically pleasing product.
  • Most moisturisers contain 65-85% water in a lotion form with water acting as an agent to disperse the active and inactive ingredients. The high water content also serves to allow absorption of some components and evaporation of the moisturiser. The water acts as a temporary hydrating agent.

Moisturisers in a cream form contain less water and more oils or occlusive agents.

Ointments are oil-based compounds with a minimum amount or no water in the product. These products are usually very occlusive and greasy. An example would be pure petroleum jelly.


The unique structure of the stratum corneum of the skin contributes to its function as a barrier to water loss and the external harsh environment. The injury to this barrier by the environment and common irritants with the resulting loss of water from the skin is the main reason for the development of dry skin or irritant dermatitis.

Moisturisers can help to increase the hydration of the skin and possibly repair/restore the barrier through the use of chemicals that are similar to the skin’s natural moisturising factors and occlusion of the skin to prevent water loss.

Moisturiser Chemistry

Ingredients in Moisturisers Action

• Water: 65-85% (lotions and creams) Dilutes and disperses ingredients, evaporates from the skin surface

• Lipids: 5-35% (lotions and creams) Occlusive effect to prevent water

• Up to 100% (ointments) loss, repair lipid layers, restore (mineral oil, petrolatum, lanolin, barrier beeswax, vegetable oils, cholesterol, fatty alcohols, fatty acids, ceramides)

• Emulsifiers: 1-2% Allow water and lipids to stay (stearic acid, triethanolamine, in suspension as a lotion form quaternium 15, fatty alcohols)

• “Active Ingredients”: 0.05-15% Attract water to the skin, skin (petrolatum 30-100%, glycerine, protectants, lubricate, fill in spaces dimethicone, allantoin, urea, between cells, block UVA/UVB alpha hydroxy acids, lactic acid, sunscreens/sunblocks)

• Preservatives: 0.1 to 1% Prevent growth of microorganisms (parabens, quaternium 15, in the product imidazolidyl urea, disodium EDTA, methylisothiazoline, alcohols)

• Fragrance: 0.25% Mask the odour of the lipids or give the product a fragrant scent

Common Moisturiser Terminology (Marketing)

Anti-aging: Sunscreen/sunblock in the product.

Barrier Cream: Alter the penetration of substances such as water and chemicals into the skin by the interaction of the cream ingredients with the stratum corneum. A protective water-repellent film may form on the skin but continues to allow normal evaporation of water from the skin.

Dermatologist Tested: Does not mean anything of significance. Can use the term even if only one dermatologist tested the product.

Hypo-allergenic: May have reduced amounts of chemicals that have an allergenic potential (fragrance, preservatives) but is not a reliable term.

Non-comedogenic: The ingredients do not cause the pores on the face, chest or back to become blocked and develop comedones (blackheads). Testing of products may have been done on rabbit ears.

Oil in Water Emulsion: A small amount of oil is dissolved in water. This is a water-based product. These products are usually lotions or light creams and dissolve readily into the skin without leaving a greasy film.

Sensitive Skin Formula: There is no definition for this term. The product may have reduced fragrance or preservatives.

Therapeutic Effect: Restores the natural skin barrier to help the skin heal.

Fragrance-Free: No fragrance is used in the product. The product may actually have a masking fragrance to decrease the odour of the oils in the products.

Water in Oil Emulsion: A small amount of water is dissolved in an oil-based product (petrolatum, mineral oil, natural plant oils). These products are usually heavier creams or ointments and can act as occlusive agents by forming a film on the skin.

Have you seen Florence’s book about Cosmetic Chemistry? Take a look here.

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