Squalene is an organic compound. It is a triterpene with the formula C₃₀H₅₀. It is a colourless oil, although impure samples appear yellow. It was originally obtained from shark liver oil (hence its name, as Squalus is a genus of sharks). An estimated 12% of bodily squalene in humans is found in sebum. Squalene has a role in topical skin lubrication and protection.

Most plants, fungi, and animals produce squalene as biochemical precursor in sterol biosynthesis, including cholesterol and steroid hormones in the human body. It is also an intermediate in the biosynthesis of hopanoids in many bacteria.

Squalene is an important ingredient in some vaccine adjuvants: The Novartis and GlaxoSmithKline adjuvants are called MF59 and AS03, respectively.

Squalene is a biochemical precursor to both steroids and hopanoids. For sterols, the squalene conversion begins with oxidation (via squalene monooxygenase) of one of its terminal double bonds, resulting in 2,3-oxidosqualene. It then undergoes an enzyme-catalysed cyclisation to produce lanosterol, which can be elaborated into other steroids such as cholesterol and ergosterol in a multistep process by the removal of three methyl groups, the reduction of one double bond by NADPH and the migration of the other double bond. In many plants, this is then converted into stigmasterol, while in many fungi, it is the precursor to ergosterol.^{[citation needed]}

The biosynthetic pathway is found in many bacteria, and most eukaryotes, though has not been found in Archaea.

Squalene is biosynthesised by coupling two molecules of farnesyl pyrophosphate. The condensation requires NADPH and the enzyme squalene synthase.

Click on genes, proteins and metabolites below to link to respective articles.

Synthetic squalene is prepared commercially from geranylacetone.