WARNING: GLYCOLIC ACID CAN CAUSE DARKENED ARMPITS
BY MADAME SWEAT
It's no secret that glycolic acid is touted as a holy grail skincare ingredient by many and has gained virality on TikTok for being a multi-purpose "hack" product that can be used on the face, scalp, feet and armpits.
When it comes to the armpits, many creators have recommended it either as a replacement for deodorant, or to brighten underarm darkness. However, although many have tried it and claimed success, many others, me included, have warned against its use on the underarms as it can make the condition worse and CAUSE severely darkened armpits!
Why is it that glycolic acid can work for some and cause worse hyperpigmentation for others? In this blog, I'll share why glycolic acid for underarms is not such a good idea and whether it can be used safely or if should it be avoided altogether.
Quick answer: Yes — glycolic acid can cause darkened armpits, especially at high concentrations (7%+) used daily. It isn't formulated for underarm pH or the sensitivity of that skin, and the resulting irritation triggers the skin to produce more melanin — the opposite of the brightening effect people are chasing. If you already have dark underarms, look for a product made specifically for that area, using a gentler mechanism like kojic acid instead.
Key takeaways:
- Underarm skin sits at pH ~6.5; glycolic acid sits at pH ~3.5–4 — that mismatch drives the irritation
- Some people notice reduced odor from glycolic acid, but it is not a safe or recommended odor solution — daily underarm use is required for that effect, and daily use is exactly what causes darkening
- "Rebound hyperpigmentation" can show early results before making pigmentation worse over time — most common in melanin-rich and sensitive skin
- Kojic acid inhibits melanin production directly, without the exfoliation and irritation that trigger rebound darkening; a dedicated antibacterial wash is the safer route for odor
WHAT IS GLYCOLIC ACID?
Chances are you are no stranger to glycolic acid and have either used it or have seen people on TikTok and YouTube recommending it for your skin, hair and body care routines. Let's break it down:
Glycolic acid is a type of alpha-hydroxy acid (AHA) that is derived naturally from certain fruits, beets and sugarcane. It is a water-soluble, colorless, and odorless substance that is commonly used in skincare products for its exfoliating and brightening properties.
Glycolic acid works by breaking down the bonds between dead skin cells, allowing them to be easily removed from the surface of the skin. It also has antibacterial properties and has been proven to kill acne-causing bacteria at certain concentrations.
Glycolic acid has one of the smallest molecules compared to other AHAs which means it can penetrate deeper into the skin.
That sounds like a good thing, right? Well, not always and I'll explain why.
THE PROBLEM WITH GLYCOLIC ACID
Popular glycolic acid formulations that are being used to treat darkened armpits were simply not formulated for that area. Both the pH level and % concentrations were not designed to treat dark spot pigmentation in this highly complex area of the body.
OVEREXFOLIATION WITH GLYCOLIC ACID
We all know the saying, too much of a good thing is a bad thing. The same is true when it comes to hyperpigmentation treatments in the underarms. Over-exfoliating is a big problem when it comes to hyperpigmentation treatments as it's very easy to over-do it and sometimes you may not realize it right away.
When glycolic acid is applied to the skin, it helps to remove dead skin cells and unclog pores, which can lead to a brighter and smoother appearance. However, in the armpit area, this exfoliation can also remove the top layer of skin, weakening the skin barrier and resulting in pigmentation-causing irritation and inflammation.
CONCENTRATION IS TOO HIGH
The first mistake people make when using glycolic acid on the underarms, is using a concentration that is far too high for the sensitive and delicate underarm area (e.g. 7% or above). I even see 30% AHA acids being used on the underarms! This is surely asking for trouble.
IT'S NOT A SAFE OR EFFECTIVE WAY TO CONTROL ODOR
I'll address this directly, because it's the actual reason a lot of people reach for glycolic acid on their underarms in the first place: some have genuinely noticed a reduction in odor after using it, and I understand why. Glycolic acid does have antibacterial properties, so it can knock back some of the bacteria that causes body odor.
But I don't recommend it for this. Full stop. Getting any odor-control benefit out of it requires daily use — and daily use of glycolic acid on the underarms is precisely what causes the irritation and rashes that lead to darkening. You cannot use glycolic acid on your underarms every day. Whatever bacteria-fighting benefit it offers isn't worth what it risks doing to your skin.
If odor is what you're actually trying to solve, there are options that work just as well without that risk. An in-shower antibacterial treatment — like the Underarm Bar, with apple cider vinegar and activated charcoal — targets the same bacteria, minus the exfoliation and pH mismatch that causes the damage.
LOW PH CAUSES IMBALANCE AND IRRITATION
Underneath all of this is a simple pH mismatch. Glycolic acid is a highly acidic ingredient, with a pH level of around 3.5-4. Your underarm pH is around 6.5.
That gap forces the skin's natural barrier to work overtime just trying to reset itself — and a barrier under that kind of chronic stress is exactly the condition that sets up the rebound effect I'll explain next.
BRIGHTEN DARK UNDERARMS FAST Brightening treatments will not work without addressing the root cause. Get Madame Sweat's guide to preventing and treating dark underarms, faster.
REBOUND HYPERPIGMENTATION: WHY SOME PEOPLE SEE RESULTS AT FIRST
This is where the story gets more complicated. Some people really do see initial results — smoother skin, even a bit of brightening — and that's exactly what makes the risk so easy to miss.
Those with melanin-rich, skin of color and sensitive skin are prone to something that is called: rebound hyperpigmentation. It occurs when aggressive and harsh products (such as 7% glycolic acid) are used to treat pigmentation issues in the delicate areas of the body. This can happen from DIY and chemical brightening treatments in the underarms, bikini line and intimate areas.
Initially you do see results at first as the brightening treatment is working on the surface of the skin, however these aggressive brightening treatments will stimulate melanin production and in the long term, the pigmentation returns. In some cases, it can be even worse than before due to the increased levels of irritation and inflammation.
DON’T USE FACE PRODUCTS TO TREAT DARKENED ARMPITS
So, what can you do to prevent glycolic acid from causing darkened armpits? Firstly, we've established the skin on the underarms is different from anywhere else on the body, and as such, you need to refrain from putting facial skin products on the underarms.
For this reason, I always recommend avoiding popular chemical exfoliating products that were formulated for the face on the underarms.
Further to this, avoid DIY treatments like lemon and sugar scrubs as they can be equally harsh.
USE UNDERARM PRODUCTS FORMULATED FOR TREATING DARKENED ARMPITS
Slow, steady and gentle wins the race when it comes to treating darkened armpits. When planning your course of action for treatment options, you should first look and see if there are specialized products for the area you're treating.
A few years ago, it would have been difficult to find products that treat darkened armpits that were also specifically formulated to be gentle and effective for the delicate underarm area. This is exactly what inspired me when I was developing my underarm brightening system.
It's a two-step system that combines a kojic acid soap, formulated at a gentle and safe dose to brighten, followed by my niacinamide deodorant that also contains brightening alpha arbutin.
These two products work synergistically, combining a wash-off and leave-on system so they can be used every day and do not cause additional irritation on the underarms that leads to rebound pigmentation.
WHY KOJIC ACID IS THE SAFER ALTERNATIVE
Unlike glycolic acid, which exfoliates aggressively and strips the surface layer of skin to reveal what's underneath, kojic acid works at a different level entirely. It inhibits tyrosinase — the enzyme responsible for melanin production — before the pigment even forms. There's no exfoliation, no barrier disruption, and none of the inflammation that leads to rebound hyperpigmentation.
Look specifically for kojic acid dipalmitate — that's the stable form used in the Brightening Bar. It doesn't oxidize as quickly as standard kojic acid, which means it keeps working consistently instead of breaking down before it's had the chance to.
It's also a shower step, not a leave-on treatment. That matters for consistency: you're already standing there for 30 seconds anyway, so there's no extra step to remember — which is exactly the kind of daily consistency that treats pigmentation safely, without the all-or-nothing risk that comes with a high-strength acid.
Pair it with the Brightening Deodorant, formulated with niacinamide and alpha arbutin, if you also want your daily deodorant working toward the same result instead of undoing it.
THE TAKEAWAY
Glycolic acid is a wonderful skincare ingredient; however, I warn against its use in the underarms for its potential to cause serious irritation, inflammation, rashes and recurring hyperpigmentation that can be worse. Instead, look for underarm brightening products formulated specifically for this purpose that you know will be gentle and safe enough to use without side effects.
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FREQUENTLY ASKED QUESTIONS
Does glycolic acid always darken armpits? No — it works for some people, especially at low concentrations used occasionally. The risk rises sharply with high concentrations (7%+), daily use, and melanin-rich or sensitive skin.
What is rebound hyperpigmentation? It's when an aggressive treatment shows early results, then triggers the skin to overproduce melanin in response to the irritation — leaving pigmentation worse than before, often after weeks of apparent improvement.
Can I use my face glycolic acid product on my underarms? No. Facial skincare is formulated for facial skin pH and thickness, not underarm skin — using it there is one of the most common causes of the irritation that leads to rebound darkening.
Does glycolic acid help with body odor? Some people notice a temporary reduction, since it does have antibacterial properties. It's still not something I recommend for odor — getting that effect requires daily use, and daily use on the underarms is exactly what causes irritation and darkening. A dedicated antibacterial wash gets the same result without that risk.
What should I use instead to brighten dark underarms? A product formulated specifically for underarm skin, at underarm pH, using an ingredient like kojic acid dipalmitate that targets pigmentation without exfoliating or disrupting the skin barrier.