Your skin is an organ. Its job is to keep the outside out and hold your insides in.
The outermost layer of the outer layer of your skin, the epidermis, is called the stratum corneum. Its structure is similar to that of a brick wall: It has bricks (dead skin cells) and mortar (lipids). Just because the skin cells are dead, that doesn’t mean they are useless—they contain proteins and fats that trap water, which helps keep your skin healthy.
When skin gets dehydrated, two things happen: It becomes more vulnerable to penetration by allergens and microbes, and it becomes less effective at shedding excess cells. “Our skin really is our first defense against the outside world,” said dermatologist Papri Sarkar.
If you want to add moisture to your skin, it’s best to apply moisturizer to wet skin to trap excess water inside. According to dermatologist Cynthia Bailey, ideally your skin is already soaked—wet for more than five minutes—and you apply moisturizer within three minutes after toweling dry.
Though packaging may promise vast differences between one lotion and the next, they all include the same basic types of ingredients—occlusives, emollients, and humectants—to help your skin retain moisture.
Occlusives seal the skin to prevent water from evaporating. Petrolatum, better known as petroleum jelly, is the standard with which all other occlusives are compared. It can reduce water loss by as much as 99%. It doesn’t clog pores, allergies to it are rare, and it has a safety record spanning more than 100 years.
Other occlusives include lanolin, dimethicone, coconut oil, shea and cocoa butters, mineral oil (liquid petrolatum), botanical oils (like those from fruits, seeds, and nuts), and beeswax. Many lotions use an oil-free occlusive called dimethicone, a kind of silicone used to create a silky but non-greasy feeling.
Humectants are ingredients that draw water, primarily from deeper skin layers, to the surface of the skin. If a lotion or cream claims to be “long-lasting,” the manufacturer is probably referring to humectant ingredients such as glycerin, hyaluronic acid, alpha-hydroxy acids, urea, or lactic acid, according to Bailey.
All moisturizers with humectants must also have an occlusive ingredient so that the water pulled from deep skin layers doesn’t evaporate immediately and dry your skin further.
Many moisturizers also contain skin-softening ingredients called emollients, such as shea and cocoa butters, cetearyl alcohol, mineral oil, lanolin, and stearic, linoleic, linolenic, oleic, and lauric acids.
Manufacturers often add fragrances and dyes to lotions and creams to make them smell and look better. But lotions can be a particularly problematic vehicle for fragrances if you rub them into dry skin, which is more sensitive to irritants, as fragrances can be for some people. “Once you develop a skin allergy to an ingredient, that allergy lasts for your lifetime,” Bailey said. “Don’t taunt it.” The dermatologists we consulted recommend using only fragrance-free lotions to avoid potential allergic reactions.
When evaluating lotions, we didn’t automatically eliminate those with dyes or fragrances, since the look and smell of a lotion can be important to many people. However, for our picks we noted such additions if they appeared in the ingredient lists, and we made sure to include a larger subset of fragrance- and dye-free options in our panel testing.
Lotions can also contain ceramides, essential lipids that make up part of the natural “mortar” between skin cells. Off-the-shelf lotions usually don’t list the concentration of ceramides, so you can’t be sure whether they’ll have a real effect.
