What is lactic acid and how is it used in skincare?
Lactic acid is an alpha hydroxy acid which is commonly used in skincare thanks to its ability to gently exfoliate and hydrate the skin.
In this instalment of our acids series, we speak to some of the skin experts to find out more about the science behind lactic acid and how beauty therapists can use it in treatments and in their clients’ home routines.
What is lactic acid?
Although lactic acid doesn't technically exist in the skin, its sodium salt form (sodium lactate) does, and is part of the skin’s "natural moisturising factor". The natural moisturising factor is a group of naturally occurring humectants, including amino acids, urea, glycerin and hyaluronic acid, which supports the barrier function of the stratum corneum and helps to maintain the skin's elasticity.
Lactic acid in its true form (C3H6O3) is commonly used in topical skincare, and these days it's usually synthetically made in a lab but was traditionally created as a natural by-product of plant and dairy fermentation. Like glycolic acid, lactic acid is an alpha hydroxy acid.
What does lactic acid do to the skin?
Lactic acid has a number of benefits for the skin, including its gentle exfoliation properties. “Lactic acid causes the breakdown of the desmosomes (skin binding enzymes) to induce surface cells to be released, stimulating the exfoliation process,” says Rebecca Jones, trainer and ambassador for Noon Aesthetics.
Jones adds, “The deeper layer of skin is stimulated to increases the synthesis of collagen and glycosaminoglycans (the skin’s water carriers).”
Lactic acid has a larger molecule size than some of the other AHAs like glycolic acid, so it is gentler and can't penetrate as far into the skin. This means that it has most of its exfoliating effects on the skin's surface, therefore helping with depigmentation.
Dr Catharine Denning, a cosmetic doctor who runs a regular clinic from The Light Centre in London, says, "Lactic acid breaks the bonds between dead skin cells on the surface of the epithelium, which helps to shift superficial pigmentation (in high strengths and lower pH)."
Lactic acid can also reduce the appearance of fine lines and help stimulate ceramide formation to help strengthen the skin's barrier function.
Denning adds, "Its antioxidant properties help mop up free radicals and heavy metals that may come into contact with the skin and so protects it against DNA damage."
In addition, there is scientific evidence which shows that lactic acid can boost the skin's vitality. Cigdem Kemal Yilmaz, a chemical engineer, skincare formulator and the founder of Skin Masterclass, explains, "Research shows that treatment with 12% lactic acid resulting in increased epidermal and dermal firmness and thickness, and clinical improvement in skin smoothness and the appearance of fine lines and wrinkles.
"No dermal changes were observed after treatment with 5% lactic acid; however, similar clinical and epidermal changes were noted."
Yilmaz concludes, "The clinical evidence indicates that the topical application of lactic acid is effective for depigmentation and improving the roughness and mild wrinkling of the skin caused by environmental photodamage."
Who is lactic acid suitable for?
Lactic acid is a great treatment for pigmentation and uneven skin tone as well as dry, dehydrated and dull skin. However, if you have very sensitive skin then lactic acid can be irritating, and Denning advises against using it with clients who suffer from eczema, psoriasis and rosacea – although she says that it is safe for use with pregnant and lactating clients in a concentration of 5% or less.
Other issues could occur if the lactic acid used in skincare products is derived from dairy and clients have a dairy allergy or intolerance – so it’s important to check the provenance of your lactic acid products and to carry out a pre-treatment consultation with clients to ascertain any potential contraindications.
How should you use lactic acid?
Because lactic is a gentle exfoliant, it can be found in a multitude of home-use skincare products including cleansers, toners and serums – so there are plenty of opportunities for your clients to include lactic acid in their routines.
"In topical skincare, lactic acid can be used as part of the cleansing step or following a cleanser as a standalone ingredient up to twice a day," says Denning.
"After application, you can follow it with other leave-on products, and as always finish with sunscreen during the day, or moisturiser at night if you need it.
At home, lactic acid can also be used in a stronger formulation as a weekly wash-off, mild peel, but for greater effect clients can visit a beauty professional for a more intense peel.
Lactic acid also can boost the effects of other treatments you carry out in salon. "It works well to compliment aesthetic procedure such as needling and injectables. While you would not perform the treatments together, their benefits work in harmony to achieve results,” comments Jones.
What ingredients can you use with lactic acid?
While it’s important not to overprocess the skin by using too many exfoliants and active ingredients at the same time, lactic acid can be safely layered with most skincare ingredients.
Denning says, “It is okay to pair or alternate lactic acid with other forms of exfoliant such as salicylic acid if you find your skin’s pores tend to clog or are blemish prone.”
Hyaluronic acid is another great pairing to boost the skin’s hydration, while Yilmaz shares her preferences: “Personally, I love layering lactic acid with vitamin C (ethyl ascorbic acid), amino acids, panthenol, and green tea extract.”
However, it is not recommended to layer lactic acid with retinoids because this can irritate the skin.
Want to find out more about using different skincare ingredients? Here's everything you need to know about skin cycling.