Moisturizer and the skin barrier, without the jargon

What the skin barrier is

The outermost layer of skin works like a brick wall: flattened skin cells are the bricks, and a mix of fats — ceramides, cholesterol and fatty acids — is the mortar. When the wall is intact, it holds water in and keeps irritants out. When it is damaged, water escapes faster and the skin feels tight, rough and easily irritated.

Three kinds of ingredients

Moisturizers combine three types of ingredients. Humectants such as glycerin, hyaluronic acid and urea draw water into the skin. Emollients such as squalane, ceramides and fatty alcohols smooth and soften the surface. Occlusives such as petrolatum and dimethicone form a thin seal that slows water loss.

A good moisturizer usually has some of each; the right balance depends on your skin.

Choosing for your skin type

Oily or acne-prone skin: a light lotion or gel labelled non-comedogenic. Dry skin: a richer cream with more emollients and occlusives. Sensitive skin: a fragrance-free formula with a short ingredient list. Combination skin can take a lighter product on the forehead, nose and chin and a richer one on the cheeks.

Signs your barrier needs a break

Stinging when you apply a plain moisturizer, skin that looks shiny but feels tight, new patches of redness or flaking, or breakouts that started after you added several new actives are classic signs of over-exfoliation. Pause acids, retinoids and scrubs for one to two weeks and use only a gentle cleanser, a moisturizer and sunscreen until the skin calms down.

How to apply it

Apply moisturizer to slightly damp skin after cleansing, morning and evening. In the morning it goes under sunscreen; at night it can go before a retinoid to soften it. Drinking more water improves skin hydration only modestly — for dry, flaky skin, what you put on the surface matters more.

When it's more than dryness

Persistent itching, cracked or weeping skin, or red patches that keep coming back can be eczema or another form of dermatitis, which needs a diagnosis. Moisturizers remain an important part of managing these conditions, but alongside medical treatment, not instead of it.