Humectants, occlusives, and the three minutes after a shower

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Researched. We have not used this one long enough to give you a verdict, and we would rather say so than invent one. What follows is how it works, who it suits, and what it will not do. When we have used it properly, this page carries the verdict and the date.

CeraVe Moisturizing Cream

A body moisturizer can do three things. Most bottles do some of all three, in a ratio that decides entirely how the thing feels on your arm and whether it is still working at bedtime — and the ratio is never on the front of the bottle.

The three jobs

Humectants attract water and hold it in the outer layer. Glycerin is the workhorse: cheap, ancient, in almost everything, and almost never the ingredient named on the front. Hyaluronic acid is the one that gets the marketing budget. Urea and glycerin do much the same job for a great deal less.

Emollients sit in the gaps between the cells of the outer layer and fill them in. This is what "smooth" is, physically. Squalane, plant oils, fatty alcohols, ceramides.

Occlusives slow the rate at which water leaves. Petrolatum is the benchmark and nothing has beaten it. Dimethicone is the lighter version, and it is the reason a lotion can feel like almost nothing and still hold.

A humectant with no occlusive over it is holding water in a room with the window open. That is the most useful sentence on this page, and it is the entire reason the damp-skin rule exists.

The damp-skin rule, and what it actually rests on

The instruction is to apply within about three minutes of getting out, to skin patted rather than rubbed dry.

It is not a marketing invention. It comes out of dermatology clinics, where it is given to people whose skin genuinely will not hold water, and the mechanism is plain. At that moment there is water on the surface. The humectant has something to hold and the occlusive has something to hold in. Wait an hour in a heated room and the water has gone, and you are applying the same product to a drier starting point and asking more of it.

This is also why the same bottle appears to stop working in January. The bottle did not change. The air did.

Why the petroleum jelly has a Drug Facts panel and the body butter does not

In the United States, petrolatum, dimethicone, glycerin, allantoin, cocoa butter and colloidal oatmeal are all recognised over-the-counter skin protectant actives.

That has a visible consequence on the shelf. A plain tub of petroleum jelly carries a Drug Facts panel, because at that concentration it is filed as an over-the-counter drug. An expensive body butter containing the same occlusive at a lower level is a cosmetic, and carries an ingredient list instead.

Two products, one mechanism, two completely different-looking labels. The difference is a filing decision, not a measure of which one holds water better.

Which one you need

Humid air, skin that runs oily. A humectant-led lotion, thin, not much occlusive. A heavy balm in August is a film you will want to wash off by lunchtime, and washing it off is how the habit dies.

Dry air, winter, indoor heating, skin that goes tight an hour after a shower. You need the occlusive. This is the case where a light lotion genuinely will not hold, and where people conclude they need a more expensive product when what they need is a greasier one.

Skin that is cracked or fissured — heels, knuckles in a cold snap. Occlusive, thicker than feels reasonable, and covered. Petroleum jelly under a cotton sock overnight is not a beauty ritual. It is occlusion, held in place for eight hours, and that is the whole of the trick.

What it will not do

• It does not add water to your skin. It slows water leaving and holds what is already there. That sounds pedantic until you notice it is exactly why applying to dry skin in dry air disappoints.
• It will not undo the shower. If you are coming out pink and tight, the moisturizer is repairing damage that did not have to happen, and the cheaper fix is upstream.
• It will not perform in proportion to its price. Less so here than anywhere else on the shelf. Petrolatum costs almost nothing and beats almost everything at the one job it does. That arithmetic is laid out in full on toner pads against a bottle and a cotton round, and the shape of it is the same in this aisle: you are usually paying for the texture and the smell, and both are real, and neither is the mechanism.

How much

More than you are using.

The commonest mistake in body care is not the wrong product. It is a coin-sized amount spread thin over an entire leg. A body has a great deal more surface area than a face, and the tub should visibly go down. If a body moisturizer has lasted you six months, it is not working, and that is not the formula's fault.

The thing that decides whether this works

Doing it before you get dressed, rather than later.

The three minutes is not a superstition and it is not an aspiration. It is the difference between a product used as designed and the same product applied to a dry surface an hour afterwards, which is a different and worse proposition — and the one most people are quietly running when they decide body moisturizer does not do much.

The product

It is the clearest example of all three jobs in one tub: glycerin second on the ingredient list, petrolatum third, ceramides doing the middle job. It is fragrance-free, it is sold everywhere, and it does not claim anything the ingredient list cannot account for.

The one people are searching for is the CeraVe Moisturizing Cream.

CeraVe Moisturizing Cream

We do not print prices here, because a price we typed last month is a price that is wrong today.

Written by JamieG in Garner Town, Tennessee.