Humectants are frequently used in cosmetics as a way of increasing and maintaining moisture in the skin and hair, in products including shampoo, conditioner, frizz serum, lotions, creams, lip treatments, cleansers, after-sun lotion, and some soaps or body lotions. As hygroscopic moisturizers, humectants work by attracting water to the upper layer of the skin (stratum corneum). All humectants have common hydroxyl groups which allow them to participate in hydrogen bonding and attract water. This process attracts moisture from the outer layer of the skin or, in high humidity, from the atmosphere. The moisture is then trapped against the epidermis or the shaft of the hair, depending on where the humectant is applied. Various humectants have different ways of behaving because they differ in water binding capacity at different humidities.