Dark Underarms Are Common, and Usually About Irritation

Straight answer

Dark underarms are usually caused by low-grade irritation that triggers extra pigment: friction, shaving, plucking and sometimes deodorant. Less often the cause is acanthosis nigricans, a velvety darkening linked to insulin resistance, or erythrasma, a bacterial infection. Removing the trigger, gentler hair removal and a few studied ingredients such as niacinamide, alpha hydroxy acids and retinoids can help, but expect months, not days.

Darker skin in the armpits is extremely common, and on its own it isn’t a health problem. Still, the cause matters, because the right fix for razor irritation is very different from the right fix for a sign of prediabetes. This guide sorts the usual causes of dark underarms, shows how to tell them apart, and covers what the evidence supports.

Why underarms darken

Skin responds to repeated irritation by making more melanin, the pigment that gives skin its color. Doctors call this post-inflammatory hyperpigmentation, or PIH. A 2025 systematic review of axillary hyperpigmentation in the Journal of Cosmetic Dermatology lists the usual irritants plainly: body folds, friction, hair plucking, shaving and deodorants (Vahabi et al., 2025). The armpit gets all of them, often daily.

PIH is more common and more noticeable in people with medium to deep skin tones, and the same review notes it is more prevalent in women, especially women with darker skin (Vahabi et al.). The American Academy of Dermatology (AAD) says dark spots and patches are among the most common reasons people with darker skin tones see a dermatologist (AAD). On lighter skin the same process may show up as a grayish or tan shadow rather than a deep brown one.

Common causes of dark underarms

Friction, shaving and other irritation

This is the most common story. Dull razors, dry shaving, plucking, tight sleeves and skin rubbing on skin all create small, repeated bouts of inflammation, and each one can leave a bit more pigment behind (Vahabi et al.). Deodorants and antiperspirants can play a part when a formula irritates your skin. We break these triggers down one by one in our guide to underarm discoloration triggers.

Acanthosis nigricans

Acanthosis nigricans (AN) causes brown or black patches that feel velvety and thicker than the surrounding skin. It favors body folds: the armpits, back of the neck and groin, and sometimes the elbows, knees and knuckles. It may come with skin tags, itching or odor (AAD).

According to the AAD, obesity is the most common cause, and AN can be a sign of prediabetes or diabetes. Hormone conditions such as polycystic ovary syndrome (PCOS) and thyroid disease, certain medicines (including birth control pills, strong corticosteroids such as prednisone, and niacin) and family history can also be behind it. People of Native American, African, Caribbean or Hispanic descent are more likely to develop it (AAD). Rarely, AN that appears suddenly is a warning sign of an internal cancer, which is why sudden onset calls for a prompt dermatology appointment (AAD).

Erythrasma

Erythrasma is a superficial bacterial infection caused by Corynebacterium minutissimum. It shows up as well-defined pink or brown patches with fine scaling in the armpits, groin or between the toes. It is more common in people with diabetes or obesity, in warm climates and with heavy sweating. Under a doctor’s ultraviolet (Wood’s) lamp it glows coral pink, which makes it easy to confirm, and it typically responds well to antibacterial treatment a clinician can prescribe (DermNet).

Less common causes

The systematic review notes that freckling and genetic pigment conditions such as neurofibromatosis type 1 also need to be ruled out when the pattern is unusual (Vahabi et al.). Freckles in the armpit are one of the features doctors look for in that condition, so clusters of small, flat spots there are worth mentioning at your next checkup.

Causes compared

Cause	What it looks and feels like	Other clues	What usually helps
Irritation (PIH)	Flat, even brown or gray darkening; normal skin texture	Gets worse with frequent shaving, plucking or a new product	Remove trigger, gentle hair removal, fading ingredients
Acanthosis nigricans	Darker, thicker, velvety skin; may have skin tags	Also on neck, groin; weight gain, PCOS, family history	Medical evaluation; treating the underlying cause
Erythrasma	Pink to brown patches with fine scale and sharp edges	Sweating, warm weather, diabetes; glows coral under Wood’s lamp	Antibacterial treatment from a clinician
Freckling or genetic conditions	Small, discrete flat spots	Other birthmarks or family history	Medical evaluation

Sources: Vahabi et al., AAD, DermNet.

Evidence-based care for dark underarms

Here’s what actually moves the needle. The AAD’s advice for any hyperpigmentation starts with finding the cause: when the trigger stops, many spots clear on their own and new ones stop forming (AAD). Products help, but only after that.

1. Make hair removal gentler

Shaving is the trigger most people can change today. The AAD recommends shaving on wet, softened skin with a shaving cream or gel, going in the direction the hair grows, rinsing the blade after each swipe, replacing blades after 5 to 7 shaves and storing the razor somewhere dry (AAD). Skip plucking in this area if you can; it’s on the review’s list of irritants (Vahabi et al.).

2. Reassess your deodorant

If the darkening started or worsened after a product change, or the skin stings, itches or turns red after you apply it, stop that product for a few weeks and see whether things calm down. Apply deodorant to dry, unbroken skin rather than right after shaving.

3. Use ingredients with some evidence

Studies on underarm pigmentation are small, and the review authors note there is no standard treatment (Vahabi et al.). The options with the most support:

• Niacinamide. In a randomized, placebo-controlled trial in 24 women with darker skin, a 4% niacinamide emulsion applied to the underarms produced significant improvement in color after 9 weeks, with a good to excellent response in 24% of cases versus 6% with placebo (Castanedo-Cazares et al., 2013).
• Alpha hydroxy acids (AHAs). Glycolic acid is among the topicals the review found effective (Vahabi et al.). Lactic acid is a gentler AHA that also moisturizes; see our lactic acid lotion guide.
• Retinoids, azelaic acid, kojic acid and vitamin C. The AAD lists these as ingredients that can fade dark spots (AAD). In trials of acanthosis nigricans on the neck and underarms, prescription tretinoin was the most effective topical for reducing dark pigmentation, and urea creams also helped (Alamri et al., 2025).

Introduce one active at a time and use it every second or third night at first. Underarm skin is thin and folded, so it irritates easily, and irritation is exactly what created the problem.

4. Skip these

• Over-the-counter hydroquinone. Since September 23, 2020, the FDA has considered OTC products containing hydroquinone unapproved new drugs that cannot be legally marketed, and it has received reports of rashes, swelling and ochronosis, a lasting blue-black discoloration (FDA). Prescription hydroquinone is a different conversation to have with a dermatologist.
• Unlabeled imported creams. The AAD warns that some imported products contain unlisted steroids or mercury (AAD).
• Hard scrubbing. The AAD is direct about it: vigorous scrubbing will not get rid of acanthosis nigricans (AAD). On irritated skin it adds more friction.

A simple underarm routine

The K-beauty habit worth borrowing here is restraint: few products, applied gently, every day. A routine for darkened underarms that respects how easily this skin gets irritated looks like this:

1. Shower: wash with a mild, fragrance-free cleanser. No loofah or scrub on the underarms; your hands are enough.
2. Dry completely: pat, don’t rub. Moisture trapped in a fold adds friction, and heavy sweating is a risk factor for erythrasma.
3. Hair removal, if you shave: do it at the end of the shower on softened skin, with gel and a fresh blade, in the direction of growth.
4. Night: a thin layer of a niacinamide or gentle AHA product on clean, fully dry skin, two or three nights a week to start, building up only if there’s no stinging.
5. Morning: deodorant on dry, intact skin. Skip it for a day if you’ve nicked yourself shaving.
6. Clothing: breathable fabrics and sleeves that don’t saw at the armpit during workouts.

Photograph your underarms in the same light once a month. Change is slow enough that memory isn’t reliable, and a photo record also helps a dermatologist if you end up booking a visit. For a full-body version of this approach, see our weekly body care routine.

In-office options

When the cause is irritation and topicals stall, lasers and light devices have the strongest data. In the 2025 review, the Q-switched Nd:YAG laser was the most-studied device for underarm pigmentation and improved it across three studies, usually over at least three sessions, without serious side effects. In one comparison, intense pulsed light (IPL) improved skin color by two levels in 70% of patients versus 35% with an AHA (Vahabi et al.). For acanthosis nigricans, a dermatologist may use prescription creams, retinoids or laser treatment to reduce thickness, though the AAD notes AN can be hard to treat (AAD). Choose a dermatologist experienced with your skin tone, because heat-based devices can cause new pigment changes on deeper skin.

How long fading takes

Patience is part of the treatment. The AAD says a spot a few shades darker than your natural skin color usually fades within 6 to 12 months once the cause is gone, and deeper discoloration can take years (AAD). With acanthosis nigricans, many people see the skin clear once the underlying condition is treated, though sometimes only partially (AAD). A realistic checkpoint for a new routine is 8 to 12 weeks, about the length of the trials above.

When to see a dermatologist about dark underarms

A dermatologist can often tell these causes apart in one visit, sometimes with a Wood’s lamp, and may suggest blood sugar testing if AN is suspected (AAD).

Frequently asked questions

Is it normal to have darker underarms?

Yes. Skin in body folds is often somewhat darker than surrounding skin, and repeated friction and shaving make it more so (Vahabi et al.). It’s a cosmetic concern unless it comes with thickening, scaling or a sudden change.

Can dark underarms be a sign of diabetes?

They can. Velvety, thickened darkening (acanthosis nigricans) can be a sign of prediabetes or diabetes, according to the AAD (AAD). Flat darkening with normal texture is far more often irritation.

Does shaving cause dark armpits?

Shaving and plucking are listed causes of underarm hyperpigmentation (Vahabi et al.). Shaving technique matters: wet skin, a lubricating gel, shaving with the grain and a fresh blade reduce irritation (AAD).

Can deodorant make underarms darker?

It can when a product irritates your skin; deodorants appear on the review’s list of contributing irritants (Vahabi et al.). If you notice stinging or redness, stop the product and switch to a fragrance-free option.

How long does it take for dark underarms to fade?

Mild darkening usually fades within 6 to 12 months once the trigger stops, according to the AAD, and deeper pigment can take longer (AAD).

Do home remedies like lemon juice work?

None of the popular kitchen remedies appear among the treatments studied in the 2025 systematic review (Vahabi et al.). Anything that stings can add irritation, which is the opposite of what darkened underarm skin needs.

Sources

1. Vahabi SM, Sajjadi S, Kalantari Y, et al. “Axillary Hyperpigmentation Treatment: A Systematic Review of the Literature.” Journal of Cosmetic Dermatology, 2025. pmc.ncbi.nlm.nih.gov
2. Castanedo-Cazares JP, Lárraga-Piñones G, Ehnis-Pérez A, et al. “Topical niacinamide 4% and desonide 0.05% for treatment of axillary hyperpigmentation: a randomized, double-blind, placebo-controlled study.” Clinical, Cosmetic and Investigational Dermatology, 2013. pubmed.ncbi.nlm.nih.gov
3. Alamri A, Alraddadi RA, Alzahrani D, et al. “The efficacy of topical treatments for acanthosis nigricans: a systematic review of randomized controlled trials.” Frontiers in Medicine, 2025. pubmed.ncbi.nlm.nih.gov
4. American Academy of Dermatology. “Acanthosis nigricans: Overview.” AAD. aad.org
5. American Academy of Dermatology. “Acanthosis nigricans: Signs and symptoms.” AAD. aad.org
6. American Academy of Dermatology. “Acanthosis nigricans: Who gets and causes.” AAD. aad.org
7. American Academy of Dermatology. “Acanthosis nigricans: Diagnosis and treatment.” AAD. aad.org
8. DermNet. “Erythrasma.” DermNet. dermnetnz.org
9. American Academy of Dermatology. “How to fade dark spots in darker skin tones.” AAD. aad.org
10. U.S. Food and Drug Administration. “FDA works to protect consumers from potentially harmful OTC skin lightening products.” FDA Drug Safety Communication, 2022. fda.gov
11. American Academy of Dermatology. “Hair removal: How to shave.” AAD. aad.org

General information, not medical advice. For a spot that’s new, changing or bleeding, see a dermatologist.