Beauty product ingredient lists may look like a confusing tangle of unrecognizable scientific names, but they don't have to be a mystery. Cetyl and stearyl alcohol, both typically used in hair conditioners, work together and separately with other ingredients to make hair softer and silkier after a washing.
Fatty alcohols make up part of the base of the conditioner formula. Don't think super-drying rubbing alcohol here -- that's made from ethyl alcohol or ethanol, a short-chain alcohol, and should never be used in your hair. Cetyl and stearyl alcohol are both long-chain alcohols, which are more wax-like than solvent-like, and are exactly what makes conditioner feel silky and smooth.
Both alcohols generally appear together in hair conditioners as co-surfactants, which help reduce the surface tension of water. They are sometimes listed as separate ingredients or as a preblended combination called ceto-stearyl or cetearyl alcohol.
Both ingredients help give conditioner the opaque look that protects it from sunlight, boost foaming, moisturize and have an emulsifying effect -- that is, they keep the oils and the liquids from separating in the conditioner formula.
Cetyl alcohol functions as a spreading agent -- which makes other ingredients distribute evenly throughout the mixture -- and creates the conditioner's silky texture. It appears more commonly in hair conditioners than stearyl alcohol.
Animal tallow once provided the cetyl alcohol in conditioner, but it is now derived from coconut or palm oil, or made synthetically.
Stearyl alcohol functions as a thickener and stabilizes the amount of foaming in conditioner. Conditioners with stearyl alcohol are more viscous than those without.
Stearic acid, from which stearyl alcohol is derived, can come from vegetable and nut oils or from animal fat.
If you have sensitive, allergy-prone or acne-prone skin, you may have an undesirable reaction to either ingredient. Both fatty alcohols are mildly comedogenic -- they can clog pores and cause breakouts.
If the idea of battling acne after washing your hair doesn't thrill you, first do a test patch on your skin with products that contain each type of fatty alcohol to see whether you have a reaction.