Carrier oils are oil extracts from seeds, fruit, vegetables or nuts that are rich hair emollients (moisturizers). They can also be used to “carry” essential oils, which are either too concentrated or will evaporate upon contact on their own, into the hair.
Unlike essential oils, carrier oils, which are also known as "base" oils", do not usually carry a strong scent of their own and are classified as "fixed' oils, meaning they do not typically evaporate. They can have many health properties of their own as they often contain vitamins, minerals and some essential fatty acids.
Cold-pressed oils, where the oil obtained from seeds and nuts is extracted using little to no heat, is a more expensive process, but the oils produced are considered to be a superior quality in many applications. Carrier oils produced by using a procedure called "hot extraction", in which extremely high temperatures are used to extract the oil, are often regarded as inferior as much of the oil's benefits are destroyed in the process.
Carrier oils are also available in refined and unrefined forms. Although unrefined oils are preferred in massage therapy and certain practices of aromatherapy, refined oils are generally chosen for use in cosmetic preparations so their heavier color and texture does not compete with any other ingredients.
Because carrier oils are oily in nature, they are included in many hair care products to supply additional moisture to the hair shaft. In hair care products with more natural formulations, they are considered a better base than alcohol, which can be drying, and can also assist in combating breakage, splitting and tangling.