Linoleic acid is a fatty acid that functions as an emollient and thickening agent in cosmetics and personal care products. Research has also demonstrated that linoleic acid possesses anti-inflammatory, acne reductive, skin-lightening, and moisture retentive properties when applied topically on the skin.
Linoleic acid is a polyunsaturated omega-6 fatty acid. Polyunsaturated means that the fatty acid contains more than one double bond in its backbone. Linoleic acid contains two double bonds in its 18-carbon chain. It is considered an essential fatty acid since it cannot be synthesized by the human body. However, there are many dietary sources of linoleic acid. It is abundant in many nuts, fatty seeds, and their derived vegetable oils. Linoleic acid comprises over half (by weight) of poppy seed, safflower, sunflower, corn, and soybean oils.
Linoleic acid has many important physiological activities in the human body. It is used in the biosynthesis of arachidonic acid, and thus some prostaglandins, leukotrienes, and thromboxane (TXA), which are inflammatory mediators. Linoleic acid is also a component of the skin’s lipid barrier found within the stratum corneum (the uppermost layer of skin). In fact, linoleic acid is the most abundant polyunsaturated fatty acid in the stratum corneum.
In cosmetics and personal care products, linoleic acid functions as an emollient and thickening agent. Additionally, studies have found that linoleic acid possesses anti-inflammatory, acne reductive, skin-lightening, and moisture retentive properties when applied topically on the skin.
As mentioned above, linoleic acid is a natural component of the skin’s lipid barrier, along with ceramides, cholesterol, and other fatty acids. Without these essential lipids, the barrier is weakened. A weak or damaged barrier allows harmful things like allergens, bacteria, and irritants to pass through into the deeper layers of skin, which causes symptoms of dryness, itching, and irritation. Ultimately, this can lead to the formation of skin conditions such as acne, eczema, sensitive skin, and even signs of aging. Topical application of linoleic acid helps to replenish this barrier, which softens and soothes the skin. Therefore, linoleic acid can be classified as an emollient.
Linoleic acid has been extensively researched for its anti-inflammatory properties. The majority of studies examined the effects of topical linoleic acid on inflammation during the wound healing process. For example, one study described that topical application of a solution containing 1.6 grams of essential fatty acid (mainly linoleic acid) prevented pressure ulcers in hospitalized patients. This improvement was related to better hydration and elasticity.
Linoleic acid also imparts anti-inflammatory properties through conversion to arachidonic acid, which leads to prostaglandin E2 (PGE2), possibly via peroxisome proliferative-activated receptor-a (PPAR-a) activation. PGE2 suppresses T cell receptor signaling and may play a role in resolution of inflammation. PPAR-a activation also enhances keratinocyte proliferation and lipid synthesis. This in turn enhances skin barrier repair.
There is also research that suggests linoleic acid may possess acne reductive properties.
It has been hypothesized that a relative decrease in linoleic acid in the sebum (the skin’s natural oil) could contribute to the formation of acne. A study published in Clinical and Experimental Dermatology evaluated the effects of topically applied linoleic acid on the size of microcomedones in patients with mild acne. After a one month treatment period, there was a significant effect of topically applied linoleic acid on the size of microcomedones, an almost 25% reduction in their overall size.
Linoleic acid has also been studied for its skin-lightening effects. Studies have found that linoleic can lighten dark spots on the skin due to suppression of melanin production by active melanocytes. Melanocytes are cells within the epidermis that produce melanin, the pigment that gives our skin color. Excessive melanin production, caused by factors such as UV exposure, inflammatory conditions, acne, and injuries to the skin, can lead to uneven skin tone and dark spots. Thus, by inhibiting melanin production, linoleic acid helps to lighten skin and even out the skin tone.
There are no adverse side effects to using linoleic acid topically, thus, this ingredient is safe as used in cosmetics and personal care products.
References: Wikipedia, “Linoleic Acid”, Int J Mol Sci. 2018, 19(70), Dermatology Times, “Skin barrier benefits of sunflower seed oil”, 2015, Wound Repair and Regeneration, 2004, 12(2) 235–243, Clin Exp Dermatol. 1998, 23(2) 56-58, Arch Dermatol Res (1998) 290: 375.