Dry skin lacks oil. Dehydrated skin lacks water. They can look alike, feel alike and need quite different care. A heavy cream on dehydrated skin can feel nice for an hour and change nothing by the evening.

How to tell the difference

Dehydrated skin often feels tight yet looks slightly shiny, with fine lines that appear when you pinch the cheek. Dry skin feels rough and flaky. Many people have both, and the mix shifts with the seasons.

Water first, then something to keep it there.

A simple layering order

• A water-based essence or serum on damp skin.

• A light cream to hold the water in.

• A few drops of oil at night if your skin runs dry.

Drink water, of course, but do not expect it to do the work of a good barrier. Hydration lives on the surface as much as inside.