Do Different Bacteria Produce Body Odor in Children and Teenagers?

Which microorganisms contribute to the smell of sweat in children and teenagers? A study of 30 people in the Philippines linked underarm odor to Staphylococcus epidermidis and neck odor in children to another staphylococcal species. In addition to examining bacterial DNA, the researchers cultured bacteria in collected sweat and confirmed that they could produce compounds associated with sour odors.

This 2018 study extended body-odor research, which had largely focused on adult underarms, to different developmental stages and body sites. Rather than treating the smell of sweat as a single category, it explored which bacteria could produce which compounds from which starting materials.

15 children and 15 teenagers, with three body sites measured twice

The participants were 15 children aged 5–9 and 15 teenagers aged 15–18. Each group included eight females and seven males. They showered with fragrance-free soap containing no antibacterial ingredients, and their underarms, the backs of their necks, and their scalps were examined 1 hour and 8 hours later.

In between, they took part in a 4–5-hour program alternating exercise and rest. The environment was approximately 32°C with 66% humidity, and they spent the entire eight-hour period without air conditioning. Differences between the two measurements therefore included not only exercise but also time since showering and exposure to a hot environment.

One professional perfumer rated odor intensity at each site on a scale from 0 to 100 and recorded characteristics such as sour, sulfurous, and greasy. Samples were collected from the skin using tape. The 180 samples, from 30 people × three sites × two time points, underwent shotgun metagenomic analysis, which broadly sequences microbial DNA. The study did not involve 180 people.

Teenagers’ underarms smelled stronger, with sulfurous notes after exercise

In both age groups, underarm odor was stronger 8 hours after showering than after 1 hour. Teenagers also had stronger underarm odor than children at both time points. Neck and scalp odors were generally weaker than underarm odor.

Children’s underarm odors had sour characteristics, sometimes mixed with sulfurous notes. In teenagers, sulfurous characteristics tended to predominate after 8 hours. Greasy characteristics were also observed on the scalp, showing that odor qualities differed according to the body site evaluated.

Parents’ classifications of their children as having or not having body odor did not clearly correspond to the perfumer’s intensity ratings. The main analyses therefore used the relationship between microorganisms and the odor intensity measured by the perfumer, rather than the parental classifications.

The most abundant bacteria are not necessarily those linked to odor

The most abundant underarm bacterium in both age groups was Staphylococcus hominis. However, Staphylococcus epidermidis showed a particularly notable association with underarm odor intensity. There was a clear positive correlation in the analysis combining both age groups.

On children’s necks, meanwhile, the relative abundance of S. hominis was associated with odor intensity. Even for the same bacterium, the relationship varied with body site and age group. Underarm odor also showed positive associations with bacteria such as Cutibacterium avidum, while on the neck there were patterns linking the relative abundance of certain Cutibacterium and Acinetobacter species to weaker odor.

No microorganisms associated with scalp odor were identified in this analysis. The scalp microbial community itself differed between age groups, but a difference in community composition and an explanation of odor are separate findings.

The analyses searching for microbial associations corrected for multiple comparisons and used an FDR below 0.1 as the threshold for identifying candidates. Individual associations are exploratory leads requiring further confirmation.

When bacteria were grouped at the broader genus level rather than distinguished by species, important underarm associations disappeared. Differentiating the bacteria at a finer level was therefore important in this study.

Tracing sour-odor pathways by bacterial species

The researchers pooled and analyzed collected sweat, identifying lactic acid, glycerol, amino acids, and other substances. Analysis after incubating sweat for 24 hours identified acetic acid and isovaleric acid as major odor compounds. These are candidates for explaining the sour odors observed.

They next examined metabolism-related genes identifiable from the DNA. Counting all genes together did not readily organize the results into coherent reaction pathways. However, distinguishing which bacterium each gene came from made the relationship between odor and pathways leading to acetic acid and isovaleric acid easier to see.

Specifically, pathways in S. epidermidis using substrates such as lactate, glycerol, and branched-chain amino acids attracted attention in teenagers’ underarms. On children’s necks, similar pathways were associated primarily with S. hominis. This approach considered not just bacterial names but also their metabolic machinery together with the materials available in sweat at each site.

However, detecting a gene in DNA is not the same as directly measuring how actively its enzyme is working at that moment. Culture experiments were also performed to help address this gap.

Two bacterial species produced odor compounds when cultured in sweat

Bacteria isolated from participants were added individually to filter-sterilized sweat and cultured for 24 hours at 37°C under aerobic conditions. S. epidermidis and S. hominis clearly produced acetic acid and isovaleric acid. Comparable production was not seen in C. acnes or Micrococcus luteus, which were tested alongside them.

Beyond the correlations found on skin, this result showed that the bacteria in question could actually produce odor compounds from materials in sweat. Their capacity under these culture conditions must nevertheless be distinguished from the size of their contribution on the skin.

The genetic analysis also identified candidate enzymes involved in producing the sulfurous odor compound 3M3SH. However, the original paper states that further culture-based confirmation is needed, particularly to establish whether S. epidermidis produces it. The confirmed production of acetic and isovaleric acids and the hypothesis of sulfur-compound production do not have the same level of certainty.

Summary

In this group, teenagers’ underarms smelled stronger than children’s, and sulfurous characteristics were also prominent later in a day that included exercise and other activities. Microbial associations were not uniform: S. epidermidis emerged as an important candidate in underarms, and S. hominis on children’s necks. Culture experiments also confirmed that both bacteria could produce acetic acid and isovaleric acid from sweat.

The central finding is that looking at “which metabolic pathway in which bacterium,” alongside age and body site, can provide a more detailed understanding of how odor develops. Because the study examined 30 people in the Philippines over one day, its results do not directly establish long-term developmental changes or justify recommending deodorizing products for children. Instead of treating all resident skin bacteria as something to remove, the findings offer leads for studying specific reaction pathways.

The research received a joint A*STAR and P&G research grant, and P&G funding supported the design and execution of parts of the study. Several authors disclosed that they were employed by P&G at the time, might hold company shares, and could not disclose patent activities because of employment-related confidentiality obligations.

Reference

Lam TH, Verzotto D, Brahma P, et al. Understanding the microbial basis of body odor in pre-pubescent children and teenagers. Microbiome. 2018;6:213. doi:10.1186/s40168-018-0588-z