The laser works on the hair, not on the sweat glands. Odor, though, usually goes down: with no hair, sweat has nowhere to linger and bacteria have nothing to grow on. But the studies are small and contradict each other: for some people sweating in the underarms does increase after laser, and for some of them it settles on its own or after a course of antiperspirant. Below we look at where sweat and odor come from, what exactly researchers found, and what to do if you notice a change after treatment.
Where sweat and odor come from
The skin has two kinds of sweat glands. Eccrine glands are almost everywhere on the body: they bring clear, salty sweat to the surface to cool you down. That sweat has no smell. Apocrine glands sit in the underarms and groin, open into the hair follicles and only switch on at puberty. Their sweat is thicker, and on its own it has no smell either. Odor appears when bacteria on the skin break that sweat down. According to Cleveland Clinic, underarm hair acts as a breeding ground for bacteria and holds moisture, so odor lasts longer on hairy skin.
The simple conclusion: the amount of sweat depends on the glands, the odor depends on bacteria and hair. The laser removes the hair, so it affects odor, but not the amount of sweat directly.
Sources: Cleveland Clinic, body odor
Does the laser affect sweat glands: what the studies showed
The laser heats the pigment in the hair and destroys the follicle. Sweat glands contain no pigment and are not the target. But apocrine glands open into the same follicles and sit right next to them, so whether the heat reaches them was studied separately. The results went both ways.
Turkish dermatologists in 2010 measured underarm sweat before and after a course with a 1064 nm Nd:YAG laser and found that sweating increased and stayed increased a year after the last session. They did not examine the glands themselves and called that a limitation of the study. Studies that tried lasers as a treatment for excessive sweating show the opposite picture: a 2015 review by the Canadian agency CADTH collects five small studies of 6 to 100 people, in most of them sweating decreased after the course, in one the eccrine glands were seen destroyed under the microscope, in another the glands were unchanged.
The practical takeaway: no study has measured how many people this affects. In the Turkish study sweating increased on average across the group, in the hyperhidrosis treatment studies it decreased, and Lebanese doctors collected 30 such cases in one clinic over two and a half years. The CADTH review itself says it plainly: the evidence is thin and the studies are small.
Sources: Clin Exp Dermatol 2010, Nd:YAG and axillary sweating (PubMed), CADTH 2015, laser therapy for hyperhidrosis (NCBI), Lasers Surg Med 2010, diode laser and botulinum toxin (PubMed)
Why there is usually less odor after a course
Here the data agree. Iranian dermatologists in 2020 followed 30 women who had underarm treatment with a 755 nm alexandrite laser, six sessions. By the end of the course 63% said the sweat odor was weaker, 20% noticed no change, and 17% said the odor was more noticeable. The total number of bacteria on the skin fell only slightly, but their mix changed: where the odor went away, harmless staphylococci dominated; where it got stronger, other species did.
A second study explains the mechanism. In 2016 researchers at Procter & Gamble, the maker of Gillette razors, compared how shaving, waxing and trimming with scissors affect underarm odor in men. Trimming barely helped, shaving cut odor by 57% and waxing by 75%: the closer to the skin the hair is removed, the better sweat washes off and the less is left for bacteria. The laser removes the hair from the follicle, so it works like waxing, except the result lasts months and years instead of three weeks.
Sources: J Lasers Med Sci 2020, axillary laser and skin flora (PMC), J Cosmet Dermatol 2016, hair removal and axillary odor (PubMed)
"My armpits smell after laser": what it could be
Such complaints are common in search. The causes vary.
- The mix of bacteria changed: in the Iranian study the odor got stronger for one woman in six, and their skin was dominated by different bacteria (micrococci) than the skin of those who improved (staphylococci).
- Sweating increased: the reaction described in Turkey. A Lebanese study in 2014 followed 30 people with increased sweating or odor after underarm laser: in 20% it went away on its own within six months, and in total, on its own or after 12 weeks of aluminium chloride antiperspirant, normal sweating returned in 23 of the 30.
- You stopped shaving. Hair that regrows after the first sessions holds sweat more than freshly shaved skin. Between sessions you can and should shave the underarms.
- A break from deodorant. On the day of the session and the day after, the skin is left without it, and odor is more noticeable on those days. That is not a laser effect, it is the missing usual protection.
Sources: Lasers Med Sci 2014, reversibility of hyperhidrosis after axillary laser (PubMed), J Lasers Med Sci 2020, axillary laser and skin flora (PMC)
If sweating has increased and does not settle within two or three months, see a dermatologist: an aluminium chloride antiperspirant, and for persistent sweating other treatments. There is no need to interrupt the laser course because of it, but tell your specialist.
Deodorant around the session
On the day of the session come with clean, dry skin: no deodorant, creams or oils, they get in the way of the flash. If you put on antiperspirant in the morning, wash it off before the visit. After the session the skin is warm and pink for a few hours: do not apply deodorant that day, and preferably skip it the next day too, then as usual.
For the first 1-2 days after the session no sauna, pool, hot baths or hard workouts: heavy sweat on heated skin irritates the follicles. Normal days, work and walks are fine. On getting back to training, see exercise after laser hair removal.
How we do it
Underarms are our quickest area: 15-30 minutes per visit, usually 6-8 sessions 4-5 weeks apart, the hair is dark and dense and the laser takes it well. The specialist checks your skin at every visit and sets the power for your hair type. If you have noticed changes in sweating after other treatments, mention it at the consultation. You can book underarms on their own, 800 Kč per session, or in Package S together with Hollywood.
Reviewed by: MEDULLA team