Moisturizers: Do they work?

Dry skin, by itself, isn’t a medical worry, although serious cases can result in cracks and fissures that invite infection and inflammation. The real issue is discomfort — dry skin can be sore, tender to the touch and often itchy (although not all itchy skin is dry). There’s also the rough scaly appearance lamented in many advertisements.

This is one health problem that hasn’t suffered from lack of attention: There are scores of creams and lotions for dry skin. They are sold as a moisturizer, which is more of a marketing term than a medical or scientific one. Indeed, routine skincare is a realm where there’s little science to be found. Well-controlled studies of ingredients are few and far between. Companies keep information about ingredients proprietary and are careful to limit claims for what the products do to stay within government regulatory rules.

But salespeople learned ages ago that science sells, so labels and ads often use scientific terms. Moisturizers are often billed as hypoallergenic or “allergy-tested” — even though there’s no government standard for making such a claim, so any product can do so. Some products brag about being non-comedogenic — an impressive word that means they don’t cause pimples — but that’s not saying much because almost all moisturizers on the market today use ingredients that are non-comedogenic.

The list of vitamins is supposed to get us thinking that moisturizers can nourish skin or stoke it full of antioxidants. Yet, in most cases, vitamins in moisturizers probably don’t make much difference either because the amounts used are too small to have much effect, or because the vitamins degrade with exposure to light and oxygen.

The fact is that despite the long lists of obscure ingredients and the pseudoscientific hokum, all moisturizers help with dry skin for a pretty simple reason: They supply a little bit of water to the skin and contain a greasy substance that holds it in. In fact, if greasiness weren’t a problem, we might all go back to using the solution for dry skin that our grandparents used: 100-percent white petrolatum, which some of us know as Vaseline. One reason for the proliferation of moisturizers is the continuing search for a mix of ingredients that holds in water like petrolatum but feels nicer on the skin. Many products also contain humectants, ingredients that sponge up and retain water.

The good news is that despite all the unknowns and salesmanship, you really can’t go very wrong. Almost all the moisturizers on the market will help with dry skin, and in most cases, the choice comes down to subjective experience — and simply whether you like the feel and smell (nothing wrong with that — after all, it’s your skin!).

Skin

Take a look at the drawings on page 1, and you’ll see that our skin is organized in layers. The outermost one is called the stratum corneum, which consists of cells called corneocytes and various lipids — fats — between them. The corneocytes are dead cells without nuclei, but they aren’t just deadwood. They contain various substances that hold water. For our skin to feel smooth and supple, the stratum corneum has to be at least 10-percent water; ideally, it’s 20 to 30 percent. The stratum corneum can absorb as much as five to six times its own weight and increase its volume threefold when soaked in water. Without water, the corneocytes accumulate, so skin becomes flaky instead of peeling off nicely, and the stratum corneum gets disorganized and full of cracks instead of being tightly packed.

Because moisturizers contain oil, it’s a common misconception that they are replacing lost oil. However, most young children have wonderful smooth skin, and the sebaceous glands in the skin don’t start producing oily sebum until puberty. Dry skin, therefore, is about lack of water, not oil.

Ingredients

• Water. Most moisturizers are oil-in-water emulsions, so by definition, that makes them creams and lotions. Look at the ingredient list, and you’ll see that water is often the first one listed. Some of the water evaporates when you apply the moisturizer, but some also soaks in. While the stratum corneum absorbs water nicely, it doesn’t bind it very well, so some oily substance is needed to hold it in. Applying an oily substance to the skin without also resupplying it with water — either from the moisturizer or from another outside source like a bath — is ineffective: You’d just end up with greasy skin that is still dry and cracked. In fact, the optimum way to soften skin is to soak it thoroughly first in water and then cover it with something like Vaseline. But that’s time-consuming and messy so unless your skin is extremely dry, using a moisturizer that contains water is much easier and more practical.

• Occlusives. Petrolatum and other oily substances in moisturizers are sometimes referred to as occlusives because they block the evaporation of water. Despite all the elaborate variations in moisturizers, petrolatum is still a mainstay and is often named third and fourth in the ingredient list. Many fatty or waxy substances can serve as occlusives. The commonly used ones include cetyl alcohol (a fatty alcohol), lanolin, lecithin, mineral oil, paraffin, and stearic acid. Dimethicone and cyclomethicone are silicones that function as occlusives. When products say they are oil-free, that usually means they don’t contain mineral or vegetable oil and depend on dimethicone as an occlusive instead. The effectiveness of the occlusives varies. Petrolatum is the best at holding in water, followed by lanolin, mineral oil, and the silicones.

• Humectants. Theoretically, humectants pull water into the stratum corneum both from the air and from deeper layers of the skin. However, if the humidity is low, there’s so little water in the air that almost all of the water comes from inside out. Some of the commonly used humectants include glycerin, honey, panthenol (or vitamin B5, an example of a vitamin being used for its physical, not nutritional, properties), sorbitol (which we are used to seeing as an artificial sweetener), and urea. Humectants can potentially make the skin even drier by pulling water into a damaged arid stratum corneum that doesn’t hold moisturizer. So, as a practical matter, they are almost always used with occlusive ingredients that trap the moisture the humectants draw into the stratum corneum.

• Emollients. Emollients aren’t in moisturizers to moisturize but rather to make the skin feel smooth. Many ingredients that serve as occlusives — dimethicone is a good example — and humectants do double duty as emollients. Because of rubbing alcohol (isopropyl alcohol), we tend to think of alcohols as drying — and out of place in moisturizers. But some alcohols (octyldodecanol, for example) are excellent emollients.

• Vitamins. Topical retinoic acid — a form of vitamin A — reduces fine lines and wrinkles in the skin by stimulating the production of collagen and is the main ingredient in prescription anti-wrinkle creams. But the vitamin A used in some moisturizers is retinyl palmitate, which has the virtue of being a very stable molecule but isn’t nearly as biologically active as retinoic acid. Dr. Sewon Kang, a University of Michigan researcher and retinoid expert, says there is little chance that retinyl palmitate, in the amounts found in moisturizers, has much, if any, effect on collagen and wrinkles. If retinyl palmitate has a benefit, it may be as a humectant.

Vitamin C, usually under the name ascorbic acid, and vitamin E, usually as tocopherol acetate, are added because of their antioxidant properties. Studies of topical vitamin C have shown some effects, but in high concentrations. Doubts linger about its usefulness in moisturizers because light and oxygen inactivate the vitamin C. Vitamin E as tocopherol acetate is biologically inactive and probably functions mainly as a preservative.

• Menthol. Moisturizers that bill themselves as itch remedies often contain menthol. Although menthol doesn’t attack the underlying problem, the familiar cooling sensation does seem to cancel out the itching sensation.

• Lactic acid. Skin over the heel can get especially thick, leathery, and dry. Dr. Kenneth Arndt, a Harvard dermatologist, recommends using a pumice stone or callus file to get rid of the outer layers of skin and then using a moisturizer such as AmLactin to soften it. AmLactin, an over-the-counter lotion, is 12-percent lactic acid, a heavy-duty humectant that Dr. Arndt says also loosens up adhesions so heel skin becomes more fragile and less likely to crack. Sometimes, products containing lactic acid sting.

Yes, there are lots of dubious claims and mysterious ingredients, but by trapping water, moisturizers can help you with your dry skin.