The microbiome of the axillary skin is dominated by Staphylococcus aureus, Corynebacterium, and Propionibacterium. These microorganisms compete ecologically with pathogenic bacteria and prevent their spread. The hydrolysis of sebum lipids by the commensal flora produces free fatty acids that are toxic to many pathogens. Thanks to these effects, a healthy microbiome protects the skin from infectious inflammatory diseases.

According to several studies, the axillary microbiome has a modulating effect on the severity of sweat odor. The humid environment of human axillae is characterized by liquid secretions of eccrine, apocrine, and sebaceous glands containing proteins, cholesterol, steroid derivatives, squalene, and a wide range of lipids. Sweat odor results from biotransformation of these substances by the microbiome [1]. Coryneform bacteria are the main contributors to sweat odor.

The effect of laser hair removal on the composition of the axillary microbiome and, consequently, the severity of sweat odor was studied by Fazel Z. et al. The sample consisted of 30 healthy women. The average age of the participants was 30 years [2].

Participants were asked to avoid using deodorants and antifungal or antibacterial cleansers in their armpits for the study.

An Alexandrite laser with a wavelength of 755 nm was used for epilation. All patients underwent six laser hair removal sessions with an interval of 4 to 6 weeks. The following laser treatment parameters were used for the first three sessions: spot size 18 mm, pulse duration 3 ms, and radiation density 10 J/cm². The energy density was increased to 14 J/cm² during the last three sessions. After the 3rd and 6th sessions, a microbiological study of the microbiome composition was performed.

Sweat odor severity was assessed using the criteria of "improvement," "worsening," and "no change."

The average number of bacterial colonies before laser hair removal was 17.97×10⁶. After the 3rd hair removal session, the rate decreased to 17.72×10⁶; after the 6th session, the rate decreased to 17.26×10⁶ . The results show a slight tendency to reduce the number of bacteria after laser treatment.

It should be noted that laser treatment's effect on the microbiome's representatives was quite different. A decrease in the frequency of M. luteus and S. aureus, as well as an increase in the number of S. epidermidis after laser treatment, was observed.

Most participants noted a decrease in the intensity of sweat odor by the end of the laser hair removal course. Reduction of sweat odor intensity ("improvement") was observed in 19 patients (63.3%), with no change in 6 patients (20%) and worsening in 5 patients (16.7%).

In cases of decreased severity of sweat odor, S. epidermidis strain prevailed; in cases of aggravation — M. luteus; in cases of no change — S. aureus.

The nature of the effect of laser radiation on different strains of bacteria may depend on the energy density as well as the structural properties of the membrane of the microorganism itself. It is not precisely known whether laser treatment enhances the growth of a particular strain of bacteria independently of others or whether its inhibitory effect on certain strains creates better conditions for developing a specific strain. On the other hand, differences in the response to laser radiation in different bacterial species are due to mutations in their genome or result from changes in their membrane.

Thus, using laser radiation in the axillary region to remove unwanted hair can change the microbial flora and, consequently, reduce the severity of sweat odor.

References

1. Elsaeed Eldeeb M., El Mulla K., Alshaer A., et al. The effect of long-pulsed 1064 nm Nd:YAG laser-assisted hair removal on some skin flora and pathogens: an in vivo study. Indian J Dermatol Venereol Leprol 2023; 21: 1–10.
2. Fazel Z., Majidpour A., Behrangi E., et al. Using the Hair Removal Laser in the Axillary Region and its Effect on Normal Microbial Flora. J Lasers Med Sci 2020; 11(3): 255–