What Causes Dark Armpits & How To Prevent and Treat Them

Certain deodorants can irritate the skin, and rather than that irritation causing a rash as it would in other parts of the body, you might develop darker skin instead. You're more likely to have discoloration than a rash in that area because of "the ease with which a body fold like the armpit can become irritated," explains Adam Friedman, MD, FAAD to Romper via email. People with darker complexions should be particularly cognizant of this issue: "The dark[er] one's skin type, the easier it is for even mild irritation to leave discoloration in its wake," Friedman continues.

This darkening as a result of irritation is called post-inflammatory pigment alteration, and it's extremely common; The Journal of Clinical and Aesthetic Dermatology estimates the condition impacts 45 to 83 percent of people. So if you notice your underarms getting darker, try swapping your deodorant first.

As anyone who went through puberty knows, hormones impact your skin in a variety of ways, and as it turns out, an imbalance in your hormonal output can cause skin discoloration. Skin discoloration as a result of a hormonal imbalance is called melasma, and it "occurs when the melanocytes (which are cells that cause skin pigmentation) are stimulated by abnormal levels of progesterone and estrogen," leading to increased pigment in different parts of your body according to Livestrong.

The condition springs up most commonly in women who are pregnant or those who are taking hormonal birth control, so if you notice sudden discoloration when starting a new pill or when you have a baby on the way, melasma is probably the cause. But you'll have to take a trip to the doctor to be sure.

Friedman says there are many medications that are known to cause darker underarms, "including nicotinic acid, insulin, pituitary extract, systemic corticosteroids, and diethylstilbestrol." The good news is that discoloration as a result of medication likely isn't harmful: a dark underarm is only dangerous "if it is associated with an underlying and untreated medical problem," reiterates Friedman. It's still best practice to see a professional to make sure your medication is the cause, though.

Another common cause of darker pigmentation in the underarms is dead skin cells. When dead skin cells collect, they increase the pigmentation process, and the underarms are particularly sensitive to accumulation of dead cells. Luckily, there's an easy fix; Healthline recommends regular exfoliation to remove dead skin cells from the body, which will lighten the skin's appearance if that's the cause of the apparent darker color. You can use a body scrub or even a facial exfoliator to fix the problem.

Shaving your armpits is an everyday occurrence for many women, so you might not have realized the habit is most likely the cause of your skin discoloration. "The most common cause [of underarm discoloration] is post-inflammatory hyperpigmentation from irritation — generally caused by shaving, rubbing, or scratching," Dr. Nazarian says. Your razor could be irritating your skin, or it could be your hair itself making your skin appear darker. Shaving only removes surface level hair, so if your hair color is darker than your skin tone, "your skin can appear to have a dark stain, but it’s really just subsurface hair," Women's Health explains.

To prevent the discoloration, you can try using an epilator or waxing instead of shaving to remove your hair, as both of those options pull hair from the root instead of just the surface level. Alternatively, you can just stop shaving and embrace your body hair. It's really up to you. To get rid of discoloration that's already there, you could talk to your doctor about laser treatment, which studies have found to be a generally safe and effective option.

Acanthosis nigricans (AN) is "a skin condition that causes one or more areas of skin to darken and thicken," and sometimes the affected skin will have a velvety feel, according to the American Academy of Dermatology. This darkening can happen in the underarms, but it can discolor other areas of the body as well, such as the back of the neck, your elbows and knees, or even underneath your breasts. It's most commonly associated with obesity, as the discoloration happens as a result of increased sugar in the body.

While the condition itself isn't contagious or dangerous, AN can be an early indicator of potentially life-threatening conditions, such as diabetes or even cancer in extreme cases. Mayo Clinic recommends seeing a doc if you notice your skin darkening in any of these areas, "especially if the changes appear suddenly." Dr. Nazarian confirms, particularly if the discoloration comes with "other changes, such as weight gain, changes in your period regularity, new hair growth, or other things that may indicate an endocrine abnormality."

AN is a common early indicator of Type 2 diabetes, in which the body doesn't process insulin as it should, according to the American Diabetes Association. The ADA explains that as someone with Type 2 tries to process insulin, their body could produce more pigment, leading to the darker skin. Contact your doc ASAP if discoloration happens quickly, especially if you have any other early symptoms of insulin resistance.

Your underarms probably won't be the first place your skin darkens if you do have diabetes, though. "The neck is a more common location in the setting of diabetes," says Friedman. "It can actually be the presenting sign of diabetes, and will improve as blood sugar control is maintained." Track changes to your body overall to ensure you're keeping tabs on anything suspicious.

As I previously mentioned, some people develop AN when they have cancer, though these cases are extremely rare. In these patients, the skin darkens as a result of a malignant tumor that is growing in the stomach, liver, or other internal organ. This condition is called malignant acanthosis nigricans as Medical News Today reported, and it's one of the easiest external symptoms that can be a flag that something is amiss internally. The discoloration would stop once the malignant tumors are removed from the body.

The risk of malignant AN is one of the many reasons you should contact your healthcare provider ASAP if you notice a sudden change in the pigmentation of your underarms. And remember to stay in touch with your body: "I think a general rule of thumb is to do self exams monthly or every other month in general for skin cancer surveillance, and checking one's armpits is part of that," says Friedman. You may be experiencing the change because of something harmless like your deodorant or shaving, but it's better to be safe than sorry.