Hydration Is Not Moisture

This is the most useful distinction in skincare and almost nobody makes it, including people who sell skincare for a living.

Hydration is water content. Dehydrated skin is thirsty skin. It can happen to anyone, including someone with skin so oily they blot twice a day.

Moisture is lipid content. Dry skin lacks oil. It has no lid on the pot, so whatever water is in there escapes.

Dry is a skin type. You are largely born with it. Dehydrated is a condition. You did it to yourself, usually with a cleanser that squeaks, and you can undo it in about a week.

Here is why this matters so much

The most miserable people I meet at the counter are oily and dehydrated at once. Their skin is producing oil frantically because it is desperately trying to compensate for water it does not have. So they buy something for oily skin, which strips them further, which makes them produce more oil. Round and round.

They do not need a stronger cleanser. They need water, and then a light seal to keep it there.

How to tell which one you are

• Dehydrated — skin feels tight, looks dull, fine lines are more visible than usual, and it can still be shiny. Tightness is the tell.
• Dry — flaking, rough texture, visible loss of suppleness, and it is like this most of the time regardless of what you do.

What each one actually needs

For hydration: humectants. Hyaluronic acid, glycerin, urea. These pull water in. One critical thing almost nobody is told: apply them to damp skin, and always seal on top. In a dry room, a humectant on bare dry skin will pull water out of your skin instead of into it.

For moisture: occlusives and emollients. Squalane, ceramides, shea, dimethicone, petrolatum. These are the lid.

Most people need both, in that order. Water, then lid. That is the whole thing.