Why do your armpits get dark?

How shaving and deodorant cause dark patches

Inflammation can make skin produce extra melanin, the pigment that gives skin its colour. The colour left after irritation or injury is called postinflammatory hyperpigmentation. Shaving irritation, friction from tight clothes, and reactions to fragrances, dyes or preservatives in underarm products can contribute. Excessive sweating and skin conditions such as psoriasis are other possible causes. Pigmentation can remain after the original rash has healed, so the irritation and the dark patch do not have to appear together. Anyone can develop this pigmentation, but it is more common, more intense and longer lasting in darker skin tones.145

What does thick, velvety skin mean?

Acanthosis nigricans changes texture as well as colour. Patches are darker, thicker and often dry, with a velvetlike feel. They commonly affect the armpits, neck and groin, and sometimes have small skin tags. They often develop gradually without other symptoms. Obesity is the most common cause; other causes include diabetes, hormonal conditions and certain medicines, including steroids and the contraceptive pill. Healthy people can also develop these patches, especially people with black or brown skin. Colour alone cannot tell you which cause applies.23

When should you get dark armpits checked?

Book an appointment for new dark patches or skin changes you are unsure about. Thick, velvety patches deserve assessment even if you otherwise feel well: type 2 diabetes often has no symptoms. Insulin resistance means cells do not respond normally to insulin, the hormone that helps sugar enter cells. Acanthosis nigricans is associated with a higher risk of type 2 diabetes, but diabetes is diagnosed with blood tests, not skin colour. Mention any family history of diabetes, recent weight gain, increased thirst or frequent urination.126

Tell your doctor if dark patches accompany irregular periods, increased facial or body hair, or acne. These can occur with polyendocrine metabolic ovarian syndrome, or PMOS, previously called PCOS, which is linked to insulin resistance. A clinician can assess the symptoms together and decide whether hormone and blood sugar tests are needed. Patches that appear abruptly also need assessment; rarely, sudden acanthosis nigricans signals a more serious illness, including cancer.37

What can you do now?

Reducing the number of underarm products is a sensible first step, even if the bathroom shelf would prefer an expansion.1

1. 1Cut back on products applied to the area and choose gentler options labelled for sensitive skin or fragrance free. A natural label does not rule out fragrances, dyes or preservatives.
2. 2If deodorant causes a rash or irritation, change it. Stop using a skincare product that burns or stings. See a doctor if inflammation and itching persist.
3. 3Avoid repeated irritation and excessive exfoliation while the skin settles. Do not apply liquid bleach to dark patches.
4. 4If you suspect a prescription medicine, ask the prescriber about it rather than stopping it yourself.

Will the darkness fade?

For pigmentation caused by irritation, removing the trigger helps prevent new patches and lets existing pigment fade. General hyperpigmentation guidance puts fading at 6 to 12 months for spots a few shades darker than the surrounding skin; deeper pigment can take years. Acanthosis nigricans patches should fade over time once their cause is treated, rather than following a fixed cosmetic timetable.24

Treating the cause comes before cosmetic lightening, which gives the brightening aisle a supporting role rather than the lead. A dermatologist can consider creams such as hydroquinone or tretinoin for persistent pigmentation, or treatments that reduce abnormal thickening. Peels and lasers need careful selection because skin injury can worsen postinflammatory pigmentation.125