Why are my armpits darker?

Irritation can leave pigment behind

Shaving, tight clothing and ingredients in deodorants or shaving creams can irritate underarm skin. Fragrances, dyes and preservatives are possible triggers. Darkening that remains after a rash or irritation has healed is called postinflammatory hyperpigmentation: extra pigment left after inflammation. Inflammation stimulates the skin to make more melanin, the pigment that gives skin its colour. The resulting patches can range from light brown to black.14

Postinflammatory hyperpigmentation can affect any skin tone, but it is more common in darker skin. The colour also tends to be more intense and last longer. The original irritation can be gone while the darker patch remains, so colour alone does not tell you whether the skin is still inflamed.4

Thick, velvety skin needs a different approach

Acanthosis nigricans causes darker, thicker patches, usually in folds such as the armpits, neck or groin. The patches can feel dry and velvety, and sometimes have small skin tags. They often appear gradually without other symptoms, although itching is possible. Washing or vigorous scrubbing will not remove them.235

These patches do not automatically mean diabetes. Acanthosis nigricans also occurs in otherwise healthy people, including people with black or brown skin. Possible causes include obesity, diabetes, hormone conditions, inherited factors and medicines such as steroids or the contraceptive pill. Insulin resistance, a problem with how the body responds to insulin, is one possible underlying cause.36

What should I change first?

Use fewer underarm products while you work out what is irritating the area, rather than giving your armpits a larger skincare department.1

1. 1Review what touches the area, including deodorant, shaving cream and tight clothing. Consider whether darkening followed irritation or a rash.
2. 2Cut back on products and choose sensitive skin options without fragrance or dyes. If deodorant causes a rash, change it.
3. 3Arrange a medical appointment for new dark patches or changes you cannot explain, especially if the skin is thick or velvety.

Home remedies such as armpit detoxes have uncertain benefits, despite the name sounding like an administrative procedure. Excessive exfoliation can irritate the area. For suspected acanthosis nigricans, speak to a clinician before using dark spot treatments, because irritating products can worsen the problem.17

When should I see a doctor?

Book an appointment if itching or inflammation continues after changing deodorant. Mention irregular periods, unusual hair growth, weight gain, a family history of diabetes and any medicines you take. If thick, dark patches appear suddenly or spread quickly, seek medical assessment promptly. Rarely, rapidly developing acanthosis nigricans is associated with cancer.17

A clinician can usually recognise acanthosis nigricans by examining the skin. Blood tests can check for diabetes or other underlying problems; a skin biopsy is rarely needed. If a medicine is contributing, a clinician can consider changing it.27

Can the darker colour fade?

Treating the cause of acanthosis nigricans often improves the patches, but they do not always disappear completely. There is no fixed fading timeline. If appearance remains a concern, a dermatologist can consider creams such as ammonium lactate, tretinoin or hydroquinone. Treatment for the colour is optional when no underlying condition needs care.67

For pigment left after inflammation, lightening treatments have varying success. Peels and lasers can help some surface pigmentation, but can also worsen it by injuring the skin. They do not treat pigment deposited deeper in the skin.4