A humectant is a substance used primarily in foods and cosmetic products to help retain moisture. These substances are called hygroscopic, which means that they are able to absorb ambient water. Some humectant additives are beneficial when consumed or used. Others, particularly in some foods, are less helpful, may cause abdominal distress, and should probably be avoided.

A common humectant in food products is sorbitol. This humectant is a sugar alcohol derived from sugar. It is used in dietetic or sugarless foods and is lower in calories than sugar, so it is a popular choice among those who are dieting. In doses larger than 1.76 ounces (50 g), it has a laxative effect and can cause diarrhea. In the 1990s, consumer advocates successfully lobbied to have product warnings placed on foods containing sorbitol, so people could keep their consumption below harmful levels.

Polydextrose is another humectant food additive used to replace sugar. It is not only found in sweet foods, but frequently in other foods like salad dressings. This particular humectant not only replaces sugar in some foods, but can also be used as a fat or starch replacement. It has a laxative effect as well, so reading the labels of one’s food can inform selection.

Glycerol can be found in foods, but is also sometimes specifically prescribed by doctors for constipation, so again cautious consumption is advised. Perhaps the most beneficial aspect of glycerol is not as a humectant but in the manufacture of biodiesel. With current shortages in oil and rising gasoline prices, many have turned to fuel alternatives like biodiesel, and it is predicted that many more will do so.

Glycerol or glycerin is a frequent addition to moisturizing lotions and skin creams. Some humectants used in skin care products are vegetable oil based. Many work well for moisturizing and smoothing the skin. A humectant like mineral oil, however, can actually build up under the skin and prevent the skin from absorbing essential vitamins and nutrients. A number of skin products contain mineral oil, even the more highly priced ones. Consciousness of the deprivation of nutrients to the skin caused by mineral oil has prompted something of a skincare revolution, in which vegetable oils replace the inadvisable mineral oil.

Certain humectant substances can be added to plants at the root level to assist the plant in gathering more ambient moisture. Many gardeners favor this as a way to conserve water. A humectant composed of several oils is also used in embalming fluids. They are said to restore moisture and produce a more life-like appearance for those who will be viewed in open caskets.