Trehalose

Trehalose is a naturally occurring sugar used in skincare as a humectant and skin-conditioning agent. Chemically it is a disaccharide — two glucose units joined by an unusual alpha,alpha-1,1 linkage that keeps both sugar rings locked shut. That structural quirk makes it a non-reducing sugar, and it is the reason trehalose behaves very differently in a formula from ordinary table sugar.

It occurs widely in nature: in baker's and brewer's yeast, in mushrooms such as shiitake and oyster, in sunflower seeds, in many bacteria, and in insects, where it circulates as a blood sugar. It is best known for its role in organisms that tolerate near-total drying out — resurrection plants, brine shrimp cysts and baker's yeast among them — which build up trehalose in their tissues as they dehydrate and revive once water returns.

The trehalose used in cosmetics is not harvested from mushrooms. It is produced industrially by converting starch, usually from maize, with enzymes, and arrives as a highly purified white, odourless powder. The same material is used in food and as a stabiliser for freeze-dried pharmaceuticals, so its behaviour is unusually well documented.

On an ingredients list it appears simply as Trehalose. You will most often find it near the top of hydrating toners, essences, serums, sheet masks, eye gels and lightweight gel-creams, sitting alongside other water-binding ingredients such as glycerin, hyaluronic acid, betaine and panthenol. It is water-soluble and has no colour or scent of its own.

Trehalose works first as a humectant. Its many hydroxyl groups hydrogen-bond with water, so a film of it on the skin surface draws moisture from the formula and the surrounding air and holds it in the uppermost layers. Better-hydrated surface cells swell slightly, which is why skin looks plumper and feels smoother almost straight away.

What sets it apart is what happens as that film dries down. Two mechanisms are proposed, both worked out in freeze-drying and desiccation biology rather than on skin. In water replacement, trehalose slots into the gaps left by evaporating water and hydrogen-bonds to proteins and lipids in place of it. In vitrification, it forms a glass-like matrix that slows molecular movement almost to a halt.

Being non-reducing, trehalose cannot react with proteins the way ordinary sugars can. That gives it notable resistance to heat and acid, so it stays intact across a wide pH range and helps steady the formula around it. Laboratory studies also report that it limits markers of oxidative stress, but the mechanism is unsettled and most of that work uses cell cultures at levels far above cosmetic use, so it should not be read as a proven benefit on human skin.

Trehalose is one of the easiest ingredients to slot into a routine — water-soluble, pH-flexible, and with no meaningful interactions to plan around.

• Apply to damp skin. Humectants have more to work with when there is water already on the surface, so press a trehalose toner or serum in straight after cleansing.
• Always follow with a moisturiser. On its own a humectant can leave skin feeling tight, especially in dry indoor air or cold weather. A cream with ceramides, squalane or another emollient seals the water in.
• Layer it with anything. There is no pH requirement, so it sits happily alongside vitamin C, niacinamide, exfoliating acids and retinoids — and can make those routines feel more comfortable.
• Use it morning and night. No tolerance-building period is needed.
• Check where it sits on the INCI list. Named in the first few ingredients, there is likely enough to matter; buried at the end of a long list, less so.
• Look for humectant blends. Trehalose alongside glycerin, betaine, sodium PCA or hyaluronic acid tends to feel better than any single one on its own.