The science of hydration

The two words are used interchangeably, but they describe different things. Hydration is about the water content of skin. Moisture, in the way skincare uses it, is about oils and lipids that stop that water from leaving.

That is why drinking more water, though good for you generally, doesn't directly translate into hydrated skin. What matters is how well the outer layer holds the water it already has.

Dry skin is a skin type: it makes less oil than average. Dehydrated skin is a condition: it lacks water and can happen to any skin type, including oily skin, which is why skin can feel tight and look shiny at the same time.

The distinction matters for what you choose. Dehydrated skin needs water-binding ingredients and a barrier that holds on to them. Dry skin needs those too, plus more emollient help.

Humectants, such as glycerin and panthenol, draw water into the upper layers of skin. Emollients, such as squalane, soften and smooth. Occlusives, such as shea, form a layer that slows water loss.

Ceramides sit slightly apart: they are part of the skin's own structure, so replacing them supports the barrier itself. A routine that covers these roles, without repeating them, is usually enough.

Apply humectant-based products to slightly damp skin, then seal them in with a cream so the water has somewhere to stay. Avoid very hot water and harsh cleansers, and remember that dry indoor air is working against you in winter. In practice this is the order of the NOMA routine: The Reset, The Balance, then The Seal.