Is it OK for your underarms to be dark?

Why are your underarms darker?

Shaving irritation, tight clothing and reactions to underarm products can contribute to darkening. Dark colour left after irritation is called post inflammatory hyperpigmentation. It is part of the skin's healing process and can happen after an itchy rash or repeated friction where skin rubs against skin. The colour can remain even after the original irritation has settled.13

A different cause is acanthosis nigricans, a condition that makes skin darker, thicker and velvety, usually in folds such as the underarms, neck or groin. The patches often develop gradually, sometimes with itching or small skin tags. Acanthosis nigricans is not contagious, and scrubbing will not remove it.45

Velvety dark patches can be an early sign of prediabetes or diabetes. If you notice that texture, ask your doctor about diabetes testing rather than treating the colour alone. Acanthosis nigricans also occurs in otherwise healthy people, so dark underarms alone do not mean you have diabetes.26

When should you see a doctor?

Book an appointment for new dark patches or a skin change you cannot explain. A doctor can usually recognise acanthosis nigricans by examining the skin and can arrange tests if the cause is unclear. Possible causes include obesity, hormone conditions and certain medicines, including steroids and hormone treatments. Discuss a possible medicine change with the prescriber.5

Tell your doctor if you also have any of these changes:

• Weight gain or a family history of diabetes.
• Irregular periods or unusual hair growth.
• Inflammation or itching that persists after changing an irritating deodorant.
• Dark, thick skin that develops rapidly across several areas. This needs assessment because, rarely, acanthosis nigricans is linked to cancer.

Painful, enlarged underarm lumps need a separate medical assessment. Seek care as soon as possible if they come with fever or skin discolouration; do not treat them as a pigmentation issue.7

What can you do about the colour?

If products are irritating the area, reduce what you apply and consider a deodorant marketed for sensitive skin. Fragrances, dyes and preservatives can contribute to reactions. Products marketed as "natural" are not automatically better for dark underarms, despite the label's excellent opinion of itself.1

Avoid dry shaving, a dull blade and rushing, all of which can cause razor burn. Address repeated rubbing or other irritation rather than trying to scrub the colour away. Repeated exfoliation can also irritate the area.17

Pigmentation after irritation can take several months to fade. Skin usually returns to its previous colour once the irritation stops, but continued friction can keep the darkening going. Acanthosis nigricans often improves when its underlying cause is treated; treating that cause comes before cosmetic treatment.23

If the colour still bothers you after assessment, a dermatologist can discuss treatments to improve its appearance. Options include creams containing ammonium lactate, tretinoin or hydroquinone. Lightening creams should be used only on limited areas and as directed by your doctor, rather than spread broadly across irritated skin.23