Is this cause for concern?

Your underarms should naturally be about the same shade as the rest of your skin. But sometimes, the skin in the armpits can turn a darker hue. Dark underarms usually aren’t a sign of anything serious, but some people may find them embarrassing — especially during tank top and swimsuit season.

Darkening is often due to a skin condition called acanthosis nigricans (AN). It causes skin to thicken and darken in folds around the body.

Common areas of darkening include the:

  • armpits
  • back of the neck
  • groin
  • elbows
  • knees

Your skin might also itch or have a foul odor in those areas.

Anywhere from 7 to 74 percent of people experience some form of AN, according to a 2014 overview of the condition. The likelihood of developing dark underarms often depends on factors like race, health, and family history.

Keep reading to learn more about why this happens and what you can do.

What causes this condition, and who’s at risk?

Your skin color is determined by pigment cells called melanocytes. When these cells multiply more, they can turn the skin a darker color.

Anyone can develop AN, but some people have a greater risk. People who have darker skin are more likely to have darkening under their arms than people with lighter skin.

AN sometimes runs in families. You inherit it via a faulty gene. You’re more likely to have dark patches on your skin if you have a parent, sibling, or other close relative with the condition.

Although AN is usually genetic or tied to an underlying condition, there’s some evidence to suggest that hair removal may also be a culprit. It’s thought that irritation from repeated shaving or plucking might stimulate excess melanocyte production.

To avoid irritating your underarms, lubricate the skin with a gentle soap or shaving cream before shaving. Apply an unscented moisturizing cream afterward.

You may also be more likely to develop AN because of:

Obesity

Carrying extra weight makes your body more resistant to the effects of insulin. This hormone helps regulate your blood sugar. High levels of insulin in your blood can lead to increased production of skin pigment cells.

More than half of adults who are 200 percent or more over their ideal body weight experience darkening in their underarms and other skin folds.

Type 2 diabetes

Obesity is also a risk factor for type 2 diabetes, a disease of high blood sugar. People who develop type 2 diabetes are at an increased risk of AN.

Hormone syndromes

Some conditions that disrupt insulin levels can lead to AN.

This includes:

Medication

Certain medications increase your insulin levels, which can lead to underarm darkening.

This includes:

Cancer

In rare cases, sudden skin darkening could be a sign of cancer. When this happens, it often affects the stomach, liver, or colon. These tumors increase levels of growth factors that stimulate skin pigment cells.

When AN is caused by cancer, it’s called malignant acanthosis nigricans. You’ll likely see dark patches around your mouth.

How is it treated?

Often, treating the medical condition that caused your dark underarms will fix the issue. A combination of medicines and home remedies could help lighten the color.

Lifestyle changes and home remedies

Obesity is one of the leading causes of dark underarms. Losing weight can often fix the problem. Weight loss is an effective way to treat diabetes, too. Talk to your doctor about diet and fitness strategies to help you get down to a healthy weight for your height.

If you suspect that a medication you’re taking is causing your dark underarms, talk to your doctor about switching to another one.

Natural remedies

A few natural remedies have been promoted for lightening pigmented skin, including:

  • sea cucumber extracts
  • curcumin
  • milk thistle extract

These products haven’t been proven to lighten dark underarms, and some of them might cause side effects. Talk to your doctor or dermatologist before using any natural remedy.

Medication and procedures

Your dermatologist can prescribe medications to help lighten the skin under your arms.

Popular options include:

  • Retinoid creams or pills. Tretinoin (Retin-A) is considered the first-line treatment for AN. When used regularly, it can help thin and lighten the skin in affected areas.
  • Chemical peels. Peels containing trichloroacetic acid (TCA) can help exfoliate the skin. This process helps remove the thicker, damaged skin to reveal new, smooth skin.
  • Calcipotriene (Dovonex). This vitamin D-based cream reduces skin pigment cells.

Dermabrasion, which resurfaces the skin, and laser therapies are also used to treat dark skin under the arms.

If you have cancer, your doctor will perform surgery to remove the tumor. Once the tumor is removed, the darkened skin will often clear up.

When to see your doctor

Although dark underarms are usually harmless, they’re worth getting checked out by a dermatologist — especially if you think you might have a condition like diabetes or an underactive thyroid gland. Treating the condition that caused it will usually make the dark skin fade.

If you suddenly see dark patches under your arms and on other areas of your skin, see your dermatologist or primary care doctor right away. This could be a sign of more serious condition, like cancer.