An article by Beautyeditor (now rebranded as The Skincare Edit) recently came to my attention, thanks to some readers who pointed me in its direction. In it, she blames polyunsaturated oils for aging, tells you to avoid them in your skincare AND diet, and tells you to use saturated fatty acids (in particular squalane) instead.

As a big fan of oils containing unsaturated fatty acids (in particular rosehip oil which is my SOS skin saviour), I had to dig into this. Here’s a closer look at the science behind oils…

The facts about unsaturated oils

Let’s start with what Beautyeditor/The Skincare Edit got right. Unsaturated fatty acids are indeed less stable than saturated fatty acids, which means they’ll have a shorter shelf life.

Fats and oils are collectively known as triglycerides. Unsaturated triglycerides oxidise more easily than saturated triglycerides because they contain more double bonds, which are more reactive than single bonds. You’ll know an oil’s been oxidised when it goes rancid and smells a bit gross. The oils will react when exposed to air, light, heat and free radicals (though adding antioxidants like vitamin E to the oil will slow this down).

Triglyceride molecules consist of 3 fatty acids (blue) linked to a glycerin molecule (purple):

It’s the fatty acids that can vary and contain double bonds. Fatty acids are divided into saturated (no double bonds), monounsaturated (1 double bond) and polyunsaturated (2 or more) fatty acids.

Here are some common fatty acids in each category:

Saturated: lauric, myristic, palmitic, stearic
Monounsaturated: oleic (omega-9), palmitoleic
Polyunsaturated: linolenic, eicosapentaenoic, and docosahexaenoic (omega-3), linoleic (omega-6)

The fatty acids can vary, so you can get a triglyceride that contains, say, 2 saturated fatty acids and 1 polyunsaturated fatty acid. Most natural fats and oils aren’t entirely saturated or monounsaturated or polyunsaturated, but very few have an even balance of all three.

Mostly saturated fats and oils include coconut oil, butter, palm oil, beef fat
Mostly monounsaturated fats and oils include avocado oil and olive oil
Mostly polyunsaturated fats and oils include fish oil and most of the common skincare oils: safflower, sunflower, rosehip, almond, hemp, and grapeseed oils

Why might unsaturated oils be bad?

So far so good, but does this instability have an effect on your skin? Here’s where her argument gets dicey.