Dark underarms: causes and treatments

Key takeaways

• Underarm darkening has several different causes, and they often overlap.
• Velvety, thick darkening that also appears on the neck can be acanthosis nigricans, a skin sign of insulin resistance that deserves a blood test.
• Shaving, waxing, tight clothing and harsh deodorants cause irritation that leaves pigment in brown skin.
• Scrubbing with lemon, baking soda or harsh exfoliants usually makes it darker, not lighter.
• Laser hair reduction can help when repeated shaving and ingrown hairs are part of the problem.

Why do my underarms look darker than the rest of my skin?

Very often the person asking is a young woman getting ready for sleeveless outfits, or a man who has noticed it at the gym. And very often they have already tried lemon, potato, baking soda and three fairness creams. So let me first explain the logic.

The underarm is a skin fold. It is warm, it sweats, the skin rubs against itself and against clothes, and we shave, wax or thread it repeatedly. Brown skin responds to any repeated irritation by making more pigment. DermNet calls this post-inflammatory hyperpigmentation and notes it is more intense and lasts longer in darker skin. So, normally, a little extra darkness in the armpit is simply what Indian skin does in a fold. The question is whether something more is going on.

What are the main causes, and how do I tell them apart?

Erythrasma is worth knowing about. DermNet describes it as a bacterial infection of skin folds, more common in warm climates, with sweating, diabetes and obesity. Under a Wood's lamp (a special UV light), it glows coral pink, which makes diagnosis quick. It is treated with antibacterial creams or washes, not lightening creams.

Acanthosis nigricans is the one I never want to miss. The NHS describes darker, thicker, velvety patches in skin folds, and lists obesity and type 2 diabetes as common causes. DermNet adds that it is linked mainly to insulin resistance and is an independent risk factor for diabetes. That is very important to understand: the dark skin is a signal from inside. I have written a full article on dark neck and acanthosis nigricans.

What should I stop doing?

Before adding anything new, remove the things that keep irritating the skin: 1. Stop scrubbing. Lemon, baking soda, sugar scrubs and loofahs injure the skin and add pigment. 2. Stop unknown fairness or mixed creams. Many contain steroids, which thin the skin and can encourage fungal infection. See my article on steroid creams. 3. Be gentle with hair removal. Shave with the hair direction, with a sharp blade and gel, not dry. If waxing leaves you red and bumpy, it may not suit your skin. 4. Change deodorants if they sting. Alcohol-heavy and strongly fragranced products can irritate. Apply on fully dry skin. 5. Wear breathable fabrics. Tight synthetic tops rub all day, especially in Mumbai humidity.

Which treatments actually help?

Once the cause is clear, treatment usually works in layers.

Treat the cause first. Antibacterial treatment for erythrasma. Antifungal treatment for a fungal rash. For acanthosis nigricans, weight, sugar and insulin come first. DermNet notes that lifestyle change and weight loss improve insulin resistance and the skin often follows. If needed, that may be a conversation about medical weight management, which you can read about on our weight loss programme page.

Then lighten the pigment, gently. Options a doctor may prescribe after examining you include: - Azelaic acid - Topical retinoids such as adapalene or tretinoin, which DermNet lists for acanthosis nigricans - Niacinamide and other gentle lightening agents - Short supervised courses of other pigment medicines where appropriate

These irritate easily in a fold, so the usual advice is to start a few nights a week.

In-clinic treatments, selected carefully. Mild chemical peels can help some people with surface pigment. Laser hair reduction helps indirectly when repeated shaving, ingrown hairs and razor bumps are the main drivers, because it reduces how often you need to remove hair. Researchers have only recently started pulling together the studies on underarm pigmentation treatments in systematic reviews, so I am honest with people that results vary and take months.

My article on laser hair reduction in Indian skin explains what laser can and cannot do.

How long does it take?

Normally, the irritation-driven darkening improves over two to four months once you stop the triggers and treat consistently. Acanthosis nigricans improves as the metabolic cause improves, which can take longer. Your underarm will probably never match the inside of your arm exactly, because skin folds are naturally a shade darker in most Indian skin. The goal is comfortable, even, healthy skin, not a different colour.

How we approach this at Dr Tvacha

Under the Second Layer Skin Plan at our Thane, Andheri, Bandra and Dahisar centres, I first find out which cause, or which mix of causes, you have. Sometimes that means a blood sugar test, which is charged at actual cost. The plan, which may include topical treatment, chemical peels or laser hair reduction, is quoted in writing before you start, and every centre has a private consultation room for the examination.

Written by

Dr Amit KarkhanisAesthetic Physician · MBBS, Dip. Dermatology (UK) · Reg. No. 2001/02/1124

Founder of Dr Tvacha, practising in Thane since 2005. Leads the weight loss and hair programmes.