Shampoo is a hair care product, typically in the form of a viscous liquid, that is used for cleaning hair. Less commonly, shampoo is available in a bar form (like a soap bar). Shampoo is used by applying it to wet hair, massaging the product into the hair, and then rinsing it out. Some users may follow a shampooing with the use of hair conditioner. The goal of using shampoo is to remove the unwanted build-up in the hair without stripping out so much sebum as to make hair unmanageable. Shampoo is generally made by combining a surfactant, most often sodium lauryl sulfate or sodium laureth sulfate, with a co-surfactant, most often cocamidopropyl betaine in water. Specialty shampoos are available for people with dandruff, color-treated hair, gluten or wheat allergies, an interest in using an "all-natural", "organic", "botanical" or "plant-derived" product, and infants and young children ("baby shampoo" is less irritating). There are also shampoos intended for animals that may contain insecticides or other medications for treatment of skin conditions or parasite infestations such as fleas.