Linolenic Acid

Linolenic acid — more precisely alpha-linolenic acid, usually shortened to ALA — is a polyunsaturated omega-3 fatty acid. Chemically it is an eighteen-carbon chain carrying three double bonds, which in its pure form makes a colourless to pale-yellow oil that stays liquid at room temperature.

ALA is one of the two fatty acids classed as essential for humans: the body cannot build it from scratch, so it has to come from the diet. The other is linoleic acid, an omega-6. Seeds are by far the richest source. Chia seed oil is roughly 60 per cent alpha-linolenic acid, with perilla and kiwi seed oils in a similar range; flaxseed (linseed) oil is around half; and walnut, hemp, rapeseed and soya oils contribute smaller amounts. Rosehip seed oil, a long-standing favourite in facial oils, is another notable source.

In skincare you will rarely see Linolenic Acid listed on its own. Far more often it arrives inside a plant oil, which is why it turns up in facial oils, balms, cleansing oils, rich night creams and after-sun products. Its cosmetic role is as a skin-conditioning agent and emollient — a lipid that softens the surface and helps skin hold on to moisture, so the complexion looks smoother and better cushioned. The independent Cosmetic Ingredient Review panel has assessed fatty acids of this type and concluded they are safe as used in cosmetics.

The outermost layer of skin behaves a little like brickwork: flattened cells set in a mortar of lipids. That mortar is built mainly from ceramides, cholesterol and free fatty acids, and it is what keeps water from escaping. Topping it up with compatible lipids is the simplest way to make dry skin feel comfortable again.

Alpha-linolenic acid works largely as one of those lipids. Spread across the surface it fills the microscopic gaps between loosening surface cells, so skin reflects light more evenly and feels smoother almost immediately. At the same time the oily film slows evaporation from the surface, which is why oils rich in ALA leave skin looking plumper and less parched, and why that tight, uncomfortable feeling after cleansing eases so quickly.

It is worth being precise about the evidence. Linoleic acid, the omega-6, is the fatty acid skin incorporates into its own barrier lipids; alpha-linolenic acid's role looks more like conditioning than structural. Animal work on topical ALA and UV-induced pigmentation exists, but how much of it carries over to human skin at cosmetic levels has not been established.

Those three double bonds also make ALA quick to oxidise, which is why formulators pair it with antioxidants.

Alpha-linolenic acid is almost always applied as part of a seed oil rather than on its own, so the practical advice is really advice about using those oils well.

• Apply to slightly damp skin. Oils work by slowing water loss, so they give more back when there is water there to hold. Press in after a serum or straight after cleansing.
• Treat it as a last step at night. ALA-rich oils sit best over water-based products; put one under a cream only if the cream is very light.
• Two to four drops is plenty for the whole face. More does not sink in any faster and can leave a slick finish under make-up.
• Daily use suits most people, though oilier or congestion-prone skin often prefers two or three nights a week.
• No pH juggling needed. Unlike exfoliating acids it is not pH-dependent, so it layers happily with retinoids, vitamin C or niacinamide — apply the active first, the oil afterwards.
• Store away from heat and light and respect the period-after-opening symbol. ALA-rich oils go off faster than most.