Oleic acid is a monounsaturated fatty acid, C18H34O2, found naturally in many plant sources and in animal products and is commonly known as Omega-9 fatty acid. It is an omega-nine fatty acid, and considered one of the healthier sources of fat in the diet. Fatty acids are converted to enegy through the process called fatty acid oxidation in liver cells. Fatty acids are used as basic building blocks of biological membranes, for long-term energy storage (the major components of triglycerides) as well as for the precursors of eicosanoid hormones. It’s commonly used as a replacement for animal fat sources that are high in saturated fat. You may find various butter and egg substitutes made with high levels of oleic acid.

Triglyceride esters of oleic acid comprise the majority of olive oil, though there may be less than 2.0% as actual free acid in the virgin olive oil, while higher concentrations make the olive oil inedible. It also makes up 36-67% of peanut oil, 15-20% of grape seed oil, sea buckthorn oil, and sesame oil, and 14% of poppyseed oil. Oleic acid is the most abundant fatty acid in human adipose tissue.

The term Oleic means related to, or derived from, oil or olive. As a fat, oleic acid is one of the better ones to consume. As a replacement for other saturated fats, it can lower total cholesterol level and raise levels of high-density lipoproteins (HDLs) while lowering low-density lipoproteins (LDLs), also known as the “bad” cholesterol. Usually switching to an oil high in oleic acid is not difficult since there are numerous sources available.

From a health standpoint, oleic acid exhibits further benefits. It has been shown to slow the development of heart disease, and promotes the production of antioxidants. One very interesting use of oleic acid is its use as an ingredient in Lorenzo’s oil, a medication developed to prevent onset of adrenoleukodystrophy (ALD), a condition effecting only young boys that attacks the myelin sheaths of the body, causing symptoms similar to those in multiple sclerosis. Though Lorenzo’s oil does not cure the condition, it can delay onset or progression of the disease in those who are not yet symptomatic.

One of the chief sources of oleic acid in foods is olive oil, perhaps one of the tastiest cooking oils. Canola and grapeseed oil are also excellent choices when you are looking to supplement the diet with oleic acid, since they are naturally high in this fat. In addition to being used as cooking oil, oleic acid is part of a number of products. It is often used to make soap and is present in a number of cosmetics.

As a cosmetic ingredient, oleic oil seems to be a great moisturizer . In fact most cosmetic companies owe their inspiration to men and women who used oleic acid in natural forms to moisturize the skin — using olive oil on the skin has been a common practice in Italy and Greece for centuries.

Oleic acid is emitted by the decaying corpses of a number of insects, including bees and ants and triggers the instincts of living workers to remove the dead bodies from the hive. If a live bee or ant is daubed with Oleic Acid, it is dragged off as if it were dead. This is why Oleic Acid is also sometimes referred as "smell of death". The repellent smell indicates to living insects how to avoid others that have succumbed to disease or places where predators lurk. This "death recognition system" based on a simple fatty acid likely evolved over 400 million years ago.

Oleic acid may help boost memory. Oleic and monounsaturated fatty acid levels in the membranes of red blood cells have been associated with increased risk of breast cancer. Oleic acid may be responsible for the hypotensive (blood pressure reducing) effects of olive oil.