Dark underarms on melanin-rich skin: why it happens and how to fade it

What causes dark underarms

Your underarm is a skin fold. Skin rubs on skin, it's warm, you sweat, and something new goes on it every morning. A 2025 review in the Journal of Cosmetic Dermatology by Vahabi and colleagues lists friction, hair plucking, shaving, deodorants and whitening agents as triggers. The authors write that chemical deodorants, shaving and friction irritate and damage the skin, and that this damage is what leads to PIH.

In practice:

• Shaving and plucking. A razor takes a little of the top layer with it. Razor bumps and ingrown hairs often heal into flat dark marks.
• Friction. Tight sleeves, workouts, arms pressed to your sides all day. Constant rubbing is enough.
• Deodorant and antiperspirant. Fragrance and other ingredients can sting on freshly shaved skin. When a product irritates your skin, it can cause dark spots.
• Lightening creams. Yes, the thing people buy to fix dark underarms is on the trigger list too.

Irritation keeps the loop goingIrritationPigmentMore irritationLoop brokenIrritation stoppedThe mark lightens

Schematic illustration · not a before-and-after or a treatment result

The colour shows up exactly where the irritation was, and it stays after the skin has healed.

When dark underarms need a doctor

Not every dark underarm is PIH. The review says to rule out other causes before trying to lighten anything, and names erythrasma among them. Those conditions need proper treatment, not a lightening product.

Acanthosis nigricans. The NHS describes dry, dark patches, usually in the armpits, neck or groin, that are thicker than normal skin and feel like velvet. Some people get small skin tags on them. The most common cause is excess weight. Others include type 2 diabetes, hormone-related conditions and some medicines. Rarely, it's linked to cancer. It's more common in people with black or brown skin. The American Academy of Dermatology (AAD) notes it can be a sign of prediabetes. Once the cause is treated, the patches should fade. A cream on its own won't fix it.

Erythrasma. A bacterial skin infection of skin folds, armpits included. DermNet describes well-defined pink or brown patches with fine scaling, sometimes mildly itchy. Under a Wood lamp they glow coral pink. A doctor treats it, for example with an antibiotic cream.

Get your underarms checked if the skin turns thick or velvety, if a dark patch spreads quickly, itches or flakes, or if you can't point to any trigger. This article is skincare guidance. It can't diagnose you.

What makes dark underarms worse

• Lemon juice, baking soda, undiluted acids. Natural doesn't mean gentle, and stinging means irritation.
• Bleaching creams and imported lightening products with vague labels. The AAD warns they can contain steroids or mercury that aren't on the label.
• Scrubbing to "get the dark off". The colour is in the skin, not sitting on top of it.
• Dry shaving, dull blades, going over the same spot again and again.
• Deodorant straight onto skin you've just shaved.

How to get rid of dark underarms, step by step

Step 4: Then let it fade

Once the irritation stops, PIH lightens by itself. Slowly. According to the AAD, a spot a few shades darker than your skin usually fades within 6 to 12 months after the cause is stopped. Deeper pigment can take years.

Which ingredients? For over-the-counter products the AAD names azelaic acid, glycolic acid, kojic acid, retinoids, vitamin C. Research on underarms specifically is thin. The 2025 review found only a handful of mostly small studies, looking at niacinamide, alpha hydroxy acids, glycolic acid and a few others. Try anything new on a small patch before you use it on the whole underarm.

Laser and IPL are options for underarms too, but only with a doctor. On darker skin, IPL can occasionally cause hyperpigmentation itself.

The general order for PIH, including on your face, is in our guide to hyperpigmentation on dark skin.

From our lab

For a formula, the underarm is a hard place to work. It's warm, it's damp, and deodorant goes on every day. That's why we would never start here with a strong lightening product, our own included. The skin has to stop being irritated first. Only then does an active ingredient stand a chance.

A shelf product stays the same at every stage. Your skin doesn't. Because Anita formulates in our own lab in Bielefeld, we can change a product when your skin needs something different. That is why Skin Protocol exists.