Underarms go dark for different reasons, and the reason decides what you do. Usually it is one of four cases: dark dots from shaved hair, a mark left by irritation, pigment where there was inflammation, or thickened velvety skin that can be a sign of a medical condition. They look similar and need different handling.
On lightening specifically: scrubs and acids in the underarm area usually make things worse, because every new injury to the skin adds new pigment. Below we go through how to tell one cause from another, what helps in each case and where the work of a laser ends.
Four causes and how to tell them apart
Colour on its own says little. The details matter: when it went dark, what came before that and whether the skin changed to the touch.
| What you see | What it usually comes from | What to do |
|---|---|---|
| Dark dots where the hair grows, skin feels normal | Shaved hair showing through the skin | Change how you remove the hair |
| First redness, burning or itching, then the colour changed | Irritation from a product, shaving or friction | Remove whatever irritates |
| Brown marks where there were spots or ingrown hairs | Pigment after inflammation | Protect the skin from new inflammation |
| Skin is darker and thicker, velvety to the touch, other folds darken too | It may be acanthosis nigricans | See a dermatologist |
Dark dots after shaving are not your skin colour
A razor cuts the hair level with the skin, and its dark base stays in the follicle and shows through. The darker and thicker the hair, the stronger the effect, and on fair skin it shows the most. The skin itself is a normal colour; it only looks darker.
Look at your underarms right after shaving, then two or three days later once the hair has grown back a little. If the dots appear with shaving and go when the hair comes out, that is what they are.
Lightening will not help here. A different way of removing hair will. Wax and an epilator pull the hair out with the root, but they bring ingrown hairs and irritation. A laser destroys the follicle itself, and over a course the dots go along with the hair. We have a separate article on ingrown hairs.
Irritation from deodorant, shaving and clothes
The second common case: first the skin goes red, burns or itches, and the colour changes afterwards. That means the underarm is reacting to something, and while the irritant is still there the colour will not even out.
The usual sources: a new deodorant or antiperspirant, especially an alcohol-based one, shaving dry skin with a blunt razor, tight synthetic clothes and friction in the heat. Shaving is covered in detail in irritation after shaving.
Take away everything new that appeared before the darkening and give the skin two to three weeks without irritants. If the redness and itching go in that time and the colour starts to even out, you have found the cause.
Pigment after inflammation
If there were spots, folliculitis or ingrown hairs in the underarm, brown marks can stay where they were. DermNet describes this as temporary pigmentation that follows injury or an inflammatory disorder of the skin. On darker skin it happens more often, looks more intense and lasts longer.
The key property of this pigment: it goes on its own if the skin is not injured again. So the task is not to bleach the mark, but to stop new inflammation from appearing. There is an article on the blog about folliculitis and how it differs from other rashes.
Why scrubs and acids usually harm the underarm
DermNet puts it this way about peels and pigment treatments, laser and IPL: for pigmentation in the epidermis they may be helpful, but they may also aggravate it by injuring the epidermis. Underarm skin is thin, folded and constantly rubbing against clothes, so an acid injures it more easily here than on an arm or a leg.
A loop forms: you scrub, the skin inflames, new pigment settles where the inflammation was, it looks darker, you scrub harder. So with any darkening the first step is a single one: remove whatever irritates the skin, and only then think about care products.
On acanthosis nigricans the American Academy of Dermatology is explicit: vigorous scrubbing will not get rid of it.
Sources: DermNet, postinflammatory hyperpigmentation, AAD, acanthosis nigricans
When it may be acanthosis nigricans
Acanthosis nigricans looks different and is worth knowing by sight. The American Academy of Dermatology describes it as a skin condition that causes one or more areas of skin to darken and thicken, with skin that feels like velvet. So it is not only the colour that changes, but the texture.
A second clue: it does not appear in the underarms only. AAD lists the places, among them armpits, the back of the neck, the groin area and skin folds, elbows, knees. It comes on slowly, taking months or years.
AAD writes that it can be a sign of pre-diabetes, which increases your risk of getting diabetes, and that it can also be caused by a medicine you are taking. Sometimes these dark patches have no connection to any medical condition. A dermatologist sorts this out: the academy advises seeing one if you notice a change to your skin, because a small change is sometimes an early warning sign.
And a separate note from AAD worth knowing: if acanthosis nigricans appears suddenly, you should make an appointment with a dermatologist immediately, because a sudden onset can be a warning sign of cancer.
Sources: AAD, acanthosis nigricans, AAD, acanthosis nigricans: signs and symptoms
Darkening during pregnancy
Pregnancy changes pigmentation on its own. DermNet reports that increased pigmentation affects 90 % of pregnant women, more strongly in women with skin of colour, and that the areas which are already pigmented darken first. After delivery this fades, but usually not completely.
Fighting that kind of darkening during pregnancy with scrubs and acids achieves nothing and does plenty of damage. Laser hair removal is not done during pregnancy at all, details in a separate article.
Sources: DermNet, skin changes in pregnancy
What a laser does here and what it does not
A laser works on the hair: it heats the pigment in the hair and destroys the follicle. It does not lighten skin.
There is an important note here. Shaved hair under the skin casts a dark shadow, and that shadow goes along with the hair. The skin stays the same colour, and the underarm looks lighter.
The second thing that goes is the reason for irritation. No shaving every other day, no nicks, no ingrown hairs or folliculitis, so no new inflammation to leave pigment behind.
What a laser does not do: it does not clear existing pigment, it does not treat acanthosis nigricans and it does not replace a visit to a dermatologist. If the skin has thickened and turned velvety, see a doctor first.
Can you have laser if the underarms are already dark
An even darker shade on its own is not a contraindication. What matters is something else: what kind of darkening it is and what state the skin is in right now.
Fresh irritation, inflammation and scabs mean the visit is postponed until the skin has calmed down. A tan in the area is also a reason to wait: on tanned skin the power is reduced, details in laser on dark and tanned skin. The full list of limits is in contraindications.
At the consultation the specialist looks at the area and decides by what they see: the shade of the skin, whether there is inflammation, what the hair is like. The power follows from that.
How we do it here
Underarms are one of our quickest areas: 15-30 minutes per visit, usually 6-8 sessions, the first ones 4-5 weeks apart and then the interval grows, price and booking here. The hair in this area is dark and thick, and the laser takes it well.
We work with a hybrid laser with contact cooling, alexandrite, diode and neodymium, so darker skin is not a reason to turn anyone away. The specialist sets the power and adjusts it at every visit, going by how the area reacted last time.
People come to us with questions about colour regularly. A laser does not lighten skin. The dark shadow from hair under the skin, though, goes along with the hair, and for many of our clients the underarms really did start to look lighter over a course.
At our salon we look at the area during the free consultation and give you our recommendation - what a laser can remove and what belongs with a dermatologist.
Reviewed by: MEDULLA team