Emollient

Emollient is a functional category rather than a single ingredient. It describes any oil, wax, butter or ester whose job is to sit on and within the outermost layer of the skin, leaving it softer, smoother and more supple. Cosmetic chemists usually sort moisturising ingredients into three families: humectants, which attract water; occlusives, which slow its escape; and emollients, which condition the skin's surface and give a product much of its texture and slip. In practice the groups overlap — plenty of emollients are mildly occlusive, and many ingredients are listed as both.

Emollients come from an unusually wide range of sources. Plant-derived options include shea and cocoa butter, sunflower, jojoba and olive-derived oils, and squalane. Mineral-derived options include mineral oil and petrolatum. Animal-derived emollients such as lanolin and beeswax are still used, though far less than they once were. Then there are the lab-made esters and silicones whose INCI names look more technical — caprylic/capric triglyceride, isopropyl myristate, cetearyl isononanoate, dimethicone — chosen largely for how they feel on skin: light and dry-touch, or rich and cushioning.

You will find emollients in almost every leave-on product on a shelf: face and body moisturisers, cleansing balms, lip balms, serums, sunscreens and make-up. They are as much a formulation tool as a skincare benefit, which is why they rarely get top billing on the front of a pack.

The top layer of skin, the stratum corneum, is often described as a brick wall: flattened cells held together by a mortar of lipids. When skin is dry, that surface becomes uneven — cells lift at their edges, leaving microscopic gaps and loose scale that scatter light and feel rough. Emollients work largely by physics: they spread into those gaps and fill them, levelling the surface off. That is why skin feels smoother almost immediately, and why it can look less dull — a flatter surface reflects light more evenly.

Alongside that, most emollients leave a light film that slows the rate at which water evaporates from the surface, a measurement usually called transepidermal water loss. The heavier and more occlusive the emollient, the bigger that effect: a fluid ester does far less than a thick, waxy butter. With less water escaping, the moisture already in the upper layers has time to redistribute, which is what keeps skin feeling comfortable rather than tight.

Some emollients — ceramides, cholesterol and certain fatty acids — closely resemble the lipids skin makes itself, so they blend into that surface film readily. Others are picked purely for sensory reasons: to make a cream glide, sink in quickly, or leave a cushioned finish.

Emollients are workhorse ingredients rather than actives, so there is no pH window to respect. Most people use one once or twice daily, morning and night.

• Apply to slightly damp skin. Straight after cleansing or a shower, while skin still holds surface water, is when an emollient film does most good.
• Layer thinnest to thickest. Water-based serums first, emollient cream next, richest balm last — an occlusive layer applied early blocks whatever follows it.
• Match the texture to the job. Light esters and squalane suit oily skin or humid weather; butters, waxes and petrolatum-based balms suit very dry skin, hands, lips and winter.
• Adjust seasonally. A richer emollient in the cold months and a lighter one in summer is a sensible default.
• If you are blemish-prone, keep the heaviest balms for body, hands and lips and use lighter textures on the face.
• Patch test a rich new formula on the inner forearm for a few days if your skin reacts easily.