Amphoteric surfactants contain a balance of both positive and negative charges. They are very gentle cleansers and are the major components of baby shampoos. They are gentle in their cleansing and do not irritate the eyes. Examples include N-alkyl-amino acids, betaines, and alkyl imidazoline compounds.
Additives are used to provide other benefits other than cleansing. Beautifiers like hydrolyzed animal proteins are used to repair split ends by electrostatic attachment to the damaged hair. Thickeners like sodium chloride are used to give more viscosity to the shampoo product. Sequestering agents like polyphosphates and ethylenediamineetetraacetic acid keep calcium, iron, and magnesium salts from precipitating on the hair shaft. Preservatives like formaldehyde are used to prevent bacterial contamination to a water-based product like shampoo. Aesthetic additives help achieve the desired color and fragrance to improve marketability of the product. Tar, selenium sulfide, zinc pyrithione, salicylic acid, sulfur, and ketoconazole are therapeutic additives to treat conditions like psoriasis, seborrheic dermatitis, and dandruff.
A shampoo formulated for oily hair has a higher percentage of anionic surfactants, and a shampoo for dry hair would have a weaker anionic component. Limp or fine hair must be treated with shampoo that has fewer conditioners that can weigh down the hair but instead have more protein additives that can provide extra body. Permed or damaged hair must have a higher percentage of amphoteric surfactants or non-ionic surfactants to preserve the more vulnerable cuticle.