Squalene

Squalene is a triterpenoid, fat-soluble compound produced by human livers as a precursor to cholesterol synthesis, which is then either secreted by sebaceous glands in the skin or bound to LDL and vLDL for transport. PMID: 20024095PMID: 19804806 PMID: 20224686

12% of bodily squalene in humans is found in sebum. It is secreted through the skin and is important in the Skin Surface that protects the body from the external environment against oxidation, ultraviolet radiation through topical skin lubrication. PMID: 4430879 PMID: 20981292 PMID: 10668494

Most plants, fungi, and animals produce squalene as a biochemical precursor in sterol biosynthesis, including cholesterol and steroid hormones in the human body.

It was originally obtained from shark liver oil and appears to be 40% Squalene by weight (hence its name, as Squalus is a genus of sharks). 

It is most found in Olive Oil (3.6-9.6 mg per gram of extra virgin olive oil), Shark Oil, Wheat Germ, and Rice Bran.PMID: 19804806 PMID: 15560931
The squalene content appears to be unaffected by heat processing.PMID: 17935291

Statins (HMG-CoA) can inhibit squalene production in vivo. PMID: 15200015

In 2020, there were concerns raised about the potential slaughter of sharks to obtain squalene for a COVID-19 vaccine.

Initially, Squalene showed a correlation between a high amount of squalene in shark fatty tissues and the absence of cancer in this species, hence gaining interest in cancer research.PMID: 19804806 PMID: 1608049
It might be playing a significant role in lower cancer rates found with the Mediterranean Diet.PMID: 15554560PMID: 18069902
Squalene can also act as a free radical, hence seems to enhance the anti-carcinogenic effect.PMID: 11060781
It shows synergism against cancer with oleic acid, another fatty acid of olive oil.
PMID: 994224
Squalene, also shows some promise in alleviating chemotherapy induced side effects.PMID: 16150433