Why are my underarms so dark?

What can cause the dark colour?

Hyperpigmentation means skin darkening from extra melanin, the pigment that gives skin its colour. Irritation or injury can leave darker marks called postinflammatory hyperpigmentation. A history of rubbing, shaving irritation or a rash in the same area helps distinguish these marks from acanthosis nigricans. Hormonal changes, including pregnancy, and some medicines can also cause hyperpigmentation.34

A burning, itchy or blistering rash points toward more than a colour change. Contact dermatitis is a rash caused by contact with an irritant or something you are allergic to. Fragrances, dyes and preservatives in deodorants, shaving creams and other underarm products can be triggers.15

Does the skin feel thick or velvety?

Acanthosis nigricans causes darker, thicker patches, usually in the underarms, neck or groin. The patches can be dry, feel like velvet and have small skin tags. They often develop gradually. The condition also occurs in darker skin tones, where thickening alongside darkening still deserves attention. Vigorous scrubbing will not remove it, and it is not contagious.267

Acanthosis nigricans is often linked to insulin resistance, when the body responds less effectively to insulin. Other associations include obesity, hormonal disorders and certain medicines, including steroids and oral contraceptives. Some otherwise healthy people develop it too, particularly people with black or brown skin. Dark underarms alone are not a diagnosis of diabetes.46

What should I do first?

Using fewer underarm products is a sensible first step, even if the bathroom shelf would prefer expansion.1

1. 1Reduce the products you apply to the area to see whether irritation settles.
2. 2If deodorant seems to trigger a rash, switch products. Look for options marketed for sensitive skin without fragrance or dyes; a 'natural' label does not mean a product lacks irritating additives.
3. 3Reduce rubbing from tight clothing, and avoid vigorous scrubbing or excessive exfoliation.
4. 4Book a medical appointment for new dark patches, thickening or changes you cannot explain.

When should I see a doctor?

Arrange a check if itching or inflammation continues after changing deodorant. Mention weight gain, a family history of diabetes, irregular periods or unusual hair growth. Seek medical care for skin that is hot, painful or leaking blood or pus. Sudden development of thick, dark patches also warrants assessment: rarely, acanthosis nigricans is associated with cancer.134

A clinician will ask when the darkening started, whether it has changed, how it feels and which medicines you take. Acanthosis nigricans can usually be recognised by examining the skin. Depending on the findings, tests can help identify the cause. Bring details of other symptoms and changes elsewhere, such as your neck or groin.56

Can dark underarms be lightened?

Underarm brightening products are not the first purchase to make, despite their obvious interest in being the first purchase. Identifying and treating the cause comes before cosmetic treatment.6

For persistent darkening, a doctor can consider creams containing ingredients such as niacinamide, retinol, kojic acid or hydroquinone. Urea or ammonium lactate can help thin an abnormally thick outer skin layer. Chemical peels and other procedures are further options. The choice depends on whether the problem is leftover pigment, thickened skin or an underlying condition.1

Expect gradual improvement rather than an overnight change. General hyperpigmentation treatments can take months, sometimes a year, to work. With acanthosis nigricans, patches should fade over time once the cause is treated. The timetable depends on the cause and treatment, not just the darkness of the patch.36