What Does Glycolic Acid Do? (And When Gentler Wins)
Glycolic acid loosens the grip between dead cells on the surface of your skin so they shed sooner than they would alone. That is the mechanism, and everything the label promises sits downstream of it. So does the part the label rarely leads with, which is that your skin burns more easily while you use it.
Key Takeaways
- Exfoliation is the whole job. The FDA's description of the class is that these products "cause exfoliation, or shedding of the surface skin". How much depends on the acid, its concentration, its pH and the rest of the formula.
- It is the smallest alpha hydroxy acid. A smaller molecule reaches further in, which is why glycolic works faster than lactic or mandelic and irritates more readily.
- The 10 percent figure everyone quotes is not an FDA limit. It comes from the cosmetics industry's own safety review panel, and it arrives with a pH condition most articles drop.
- The sun sensitivity is measured, specific and temporary. Four weeks of use raised UV reddening by 18 percent in FDA research, and the effect was gone a week after stopping.
- FATCO makes no exfoliating acid. Tallow moisturizers and cleansing oils are not an alternative to an exfoliant. The honest tallow question here is what goes on afterwards.
What Glycolic Acid Actually Does
Dead cells at the skin's surface are held together by attachments that normally release on their own. Glycolic acid interferes with that hold. Cleveland Clinic dermatology resident Angela Wei, MD, puts it plainly: it "helps loosen the connection that holds dead skin cells together on the surface of the skin". The visible results follow from faster shedding, not from anything the acid adds.
Two properties decide how strongly it acts. The first is size. It is the smallest of the AHAs, so it penetrates skin deeper than the others in the family. The same percentage of glycolic therefore feels stronger than the same percentage of lactic.
The second is pH, and this is the part that gets lost. An AHA works in its acid form, so these products are deliberately formulated below the pH your face sits at. Healthy skin surface pH averages about 4.7, measured across 330 people by Lambers and colleagues in 2006. An exfoliating glycolic product is formulated more acidic than that on purpose. Glycolic acid low in an ingredient list with no stated pH may simply be adjusting acidity, which the FDA lists as an ordinary non-exfoliating use.
What the Regulation Actually Says
Glycolic acid in a face product is a cosmetic ingredient, not a drug ingredient, and no federal monograph sets its strength. The FDA has published on it twice. Neither document is a concentration rule.
The first is a January 2005 guidance on labeling. It recommends a warning, and it says plainly that guidances "do not establish legally enforceable responsibilities". The wording it asks for is this:
Sunburn Alert: This product contains an alpha hydroxy acid (AHA) that may increase your skin's sensitivity to the sun and particularly the possibility of sunburn. Use a sunscreen, wear protective clothing, and limit sun exposure while using this product and for a week afterwards.
The second is the widely quoted 10 percent limit, and it belongs to the industry rather than the agency. What FDA publishes is the Cosmetic Ingredient Review Expert Panel's 1998 conclusion, in two tiers:
| Tier | The panel's own wording |
|---|---|
| Consumer products | Glycolic and lactic acid are "safe for use in cosmetic products at concentrations ≤10%, at final formulation pH ≥3.5, when formulated to avoid increasing sun sensitivity or when directions for use include the daily use of sun protection" |
| Salon products | They are "safe for use in salon products at concentrations ≤30%, at final formulation pH ≥3.0, in products designed for brief, discontinuous use followed by thorough rinsing from the skin, when applied by trained professionals" |
Concentration alone was never the condition. The pH and the sun protection sit in the same sentence. And the salon tier is a different category, not a stronger version of your serum. Cleveland Clinic splits them the same way, noting that in-office peels use higher concentrations. Those are usually reserved for people needing faster results or dealing with persistent conditions like hyperpigmentation and melasma.
One more line matters. Once a product is sold as an acne treatment or a skin lightener, the FDA considers it a drug rather than a cosmetic, whatever the front of the bottle says.
The Sun Sensitivity Finding, Read Properly
FDA-conducted research reported that after four weeks of application, volunteers' sensitivity to skin reddening produced by UV increased by 18 percent. The trial behind it was published by Kaidbey and colleagues in 2003. It used 10 percent glycolic acid at pH 3.5, six days a week for four weeks, on the backs of 29 subjects. That is the exact concentration and pH the industry panel calls safe, which is the point. All the subjects were Caucasian, and Kornhauser's review notes that this whole body of work was done in lighter skin types, with darker ones still untested.
The same research found the effect does not stick. One week after treatment stopped, no significant differences in UV sensitivity remained among the treated skin sites. The paper's own conclusion is that this photosensitivity "is reversed within a week of terminating treatments". That is why the label warning covers the week after you stop.
Worth keeping in proportion. FDA logged 114 adverse reports for AHA skin care products between 1992 and February 2004, most commonly burning, rash and swelling. It says the more serious reactions appear to occur most often with the products that exfoliate hardest. Daily sunscreen is not optional alongside an acid, which is the one place this overlaps with what actually works on skin aging.
When Gentler Wins
Strength is not the goal. Getting the shedding you want without provoking the skin is the goal, and a bigger molecule buys you room.
| Acid | Molecular weight | How it behaves |
|---|---|---|
| Glycolic | 76.05 | Smallest, deepest, fastest, most irritating |
| Lactic | 90.08 | Gentler AHA, also acts as a humectant |
| Mandelic | 152.15 | Larger, penetrates slowly, lower irritation |
| Polyhydroxy acids | Larger still | AHA-like results with fewer irritation responses |
Molecular weights are from PubChem. Cleveland Clinic calls lactic acid "one of the gentler AHAs, making it a good choice for sensitive skin", and pairs its exfoliating action with a moisturizing one. The 2024 alpha hydroxy acid review in Clinical, Cosmetic and Investigational Dermatology describes mandelic acid as having "a larger molecular size, penetrates skin slowly, reducing irritation". Polyhydroxy acids such as gluconolactone are the newest branch. A 2010 review led by Andrija Kornhauser, formerly of the FDA, describes them as delivering effects similar to AHAs with fewer irritation responses.
Two levers cost nothing and are usually the ones people skip. Lower the percentage before you change acids. Then lower the frequency, since Cleveland Clinic's starting advice is once or twice a week at night, working up only if your skin tolerates it. Stacking is the other trap. Layering an acid with retinol, vitamin C or a second exfoliant multiplies irritation without multiplying results, which is the reasoning behind introducing one active at a time on reactive skin.
If congestion rather than texture is the problem, the acid family matters more than the strength. Salicylic acid is oil-soluble and works down inside the pore, which is why it shows up in face washes aimed at breakouts rather than glycolic.
When the Right Answer Is Not to Exfoliate
Sometimes gentler still is not gentle enough. Cleveland Clinic names five situations to be cautious about glycolic acid: sensitive skin, dry skin, rosacea, eczema and an active skin infection. Dr. Wei's reasoning is short. If you have sensitive skin "or skin that's not healing, it could cause more irritation".
Rosacea deserves its own line, because a gentler acid is not the workaround. The American Academy of Dermatology puts glycolic acid and lactic acid together on its avoid list for rosacea-prone skin. Swapping one for the other misses the point. A calm-first routine for flare-prone skin is the better starting position, and a dermatologist is the right person to ask about actives from there.
A stripped barrier is the other case. Physician assistant Samantha Stein, PA-C, describes the risk in Cleveland Clinic's guide to facial acids as exfoliating so far that you remove "the structures that hold in water and healthy fats". Tight, stinging, flaking skin that reacts to products it used to tolerate is not under-exfoliated. Adding acid there treats the symptom as the cause.
Glycolic acid is also generally considered safe in pregnancy at low concentrations, according to Cleveland Clinic, which still advises anyone pregnant or breastfeeding to check with their own healthcare provider first.
Got Questions?
Frequently Asked Questions
Q What does glycolic acid do to your skin?
It exfoliates. Glycolic acid loosens the connections holding dead cells at the surface so they shed faster, which is what produces smoother texture and a more even tone. The FDA describes the whole ingredient class as causing exfoliation, or shedding of the surface skin. Everything else on the label follows from that.
Q Can you use glycolic acid every day?
Not at the start. Cleveland Clinic's advice is to begin once or twice a week at night and build up to nightly only if your skin tolerates it. Daily use from day one is the most common route to irritation, dryness and the sensitivity that makes people quit the ingredient entirely.
Q What should you never mix with glycolic acid?
Other exfoliants, mainly. Cleveland Clinic tells new users they may want to avoid pairing it with lactic or salicylic acid, retinol, or vitamin C serums. The reason is practical as much as chemical: if several actives go on at once and your skin reacts, you cannot tell which one to drop.
Q Is glycolic acid an AHA or BHA?
An AHA, and the smallest one. Alpha hydroxy acids are water-soluble and work across the skin surface. Beta hydroxy acids like salicylic acid are oil-soluble and get down inside pores instead. That difference, not strength, is what should decide which one you reach for.
Q Is glycolic or salicylic acid better?
Neither, and they solve different problems. Glycolic works on surface texture, tone and fine lines. Salicylic dissolves the oil inside a clogged pore, which is why acne products favor it. Choose by whether your complaint is roughness and dullness or blackheads and congestion.
Q Do I need to moisturize after glycolic acid?
Yes, and it is the step most worth getting right. Exfoliation removes surface cells and leaves the barrier more exposed, so a plain, well-tolerated moisturizer afterwards protects the result. Fragrance and further actives are the two things most likely to sting on freshly exfoliated skin.
The FATCO Alternative
FATCO does not make a glycolic acid product, or an exfoliating acid of any kind, and there is no version of this article where we should. What we make is the step after. Tallow-based face creams and cleansing oils exist to slow water loss and keep the barrier comfortable, which is a genuinely different task from exfoliation rather than a substitute for it. One honest caveat if acids have already made your skin reactive: both Myrrhaculous and Unmyrrhaculous face creams contain lavender essential oil, and Myrrhaculous adds myrrh. Neither is the pick if you are avoiding fragrance while your skin settles. Choosing a moisturizer by skin type beats choosing by hero ingredient.
