squalen

Squalene is a naturally occurring polyunsaturated hydrocarbon of the chemical class of terpenes. It is a linear C30H50 hydrocarbon (an acyclic triterpene) with six carbon–carbon double bonds.

It occurs widely in nature; notable sources include shark liver oil, olive oil, and human sebum. It is also produced by some fungi and plants and can be manufactured by fermentation with yeast as a source. Historically extracted from shark liver oil; concerns about shark conservation have driven alternative sources.

In biology, squalene is a biosynthetic precursor to sterols, including cholesterol in animals and phytosterols in plants. It is formed in the mevalonate pathway via squalene synthase and squalene epoxidase. It also functions as an antioxidant in skin.

In industry, squalene is used in cosmetics and personal care as an emollient and moisturizer; its saturated derivative, squalane, is widely used due to greater stability. It also serves as a component of some vaccine adjuvants, notably in oil-in-water emulsions such as MF59 and AS03.

Safety and sustainability: Squalene is generally regarded as safe in cosmetic use; oxidation can occur, so formulations often use antioxidants and proper packaging. Environmental concerns stem from shark-derived sources; production from plants or yeast-based fermentation is increasingly common.