Body odor is a common occurrence, and people can often remedy it at home. Although people often associate body odor with unpleasant smells, this is not always the case.
Thoroughly washing, using antiperspirants, and shaving may all assist a person in managing unwanted body odor. If symptoms persist, a doctor may recommend prescription treatments and, in some cases, surgery. Body odor and excessive sweating may also be indicators of an underlying health condition. If a person notices unexpected changes in their body odor or volume of sweat, they should consult a medical professional immediately.
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What is body odor? When to contact a doctor. Our distinct funk comes thanks to bacteria living on our skin. Bacteria take innocent, non-smelly chemicals and turn them into our human stank, a recent study shows.
Our armpits sport glands — groups of cells that produce secretions — called apocrine APP-oh-kreen glands. These are found only in our armpits, between our legs and inside our ears. They secrete a substance that might be mistaken for sweat.
The thick secretion released by apocrine glands is instead full of fatty chemicals called lipids. If you take a whiff of your underarm, you might think this secretion stinks. Scientists have been trying to figure out the source of our signature scent. They have put forward many different molecules as the source of body odor, notes Gavin Thomas. Scientists used to think that hormones might cause our sweaty smell. Then scientists thought our sweaty smell might come from pheromones FAIR-oh-moans , chemicals that affect the behavior of other animals.
This is where the bacteria come in, says Thomas. Bacteria coat our skin. Few have stinky side effects. Thomas looked at the diet of S. This germ takes up residence in your pits because it loves to dine on a chemical from the apocrine glands. Furthermore, sebaceous glands that secrete an odorless oily matter called sebum into hair follicles pH 4.
Thus, body odor is generally considered significant only in post-pubescent subjects and adults and has primarily been studied within axilla where apocrine glands outnumber eccrine glands by a factor of Most studies on malodor have been conducted in temperate climates and on subjects from Europe and North America.
Asians, particularly those of East Asian heritage, are believed to be genetically predisposed to lower malodor [ 15 , 16 ]. However, tropical environments that are hot and humid can increase sweat production and associated incidence of malodor.
Based on extensive surveys in a Southeast Asian context, we identified that body odor is indeed a significant issue in pre-pubescent children and teenagers, both in terms of parent-reported scores as well as expert evaluations Additional file 1 : Table S1. The impact of malodor during childhood on the emotional, social, and psychological well-being of subjects is an uncharted field but it is likely to be of greater concern than adult malodor.
Furthermore, as apocrine gland secretion is inactive in children, the host-microbial metabolic interactions that lead to malodor remains unexplained.
To address this subject, we recruited a cohort of pre-pubescent children and teenagers in the Philippines who were assessed by a professional perfumer for recording odor intensity range 0— and character e.
The study design incorporated sampling from multiple body sites neck, underarm, head associated with body odor, as well as multiple time points after bath and outdoor activity, to systematically understand the microbial basis of body odor in these individuals.
In total, samples were subjected to deep whole-metagenome sequencing analysis, allowing us to study bacterial, viral, and eukaryotic community members and their functional association with malodor. Multi-modal analysis, combining regression to odor intensity and differential signatures before and after outdoor activity, was used to identify microbial taxa and functions associated with malodor in children 5—9 years and teenagers 15—18 years.
These signatures have some overlap e. While the underarm axilla has been the primary site of investigations for malodor, consumer studies suggested that malodor from the neck nape and head mid-scalp areas were also regions of concern for families and were therefore included in this study Additional file 1 : Table S1.
Subjects were assessed at two timepoints, separated by 7 h of rest and exercise to generate sweat, providing a well-suited experimental setup to account for inter-host variability and investigate how microbes convert sweat precursors into malodor Fig. In addition, the first timepoint was taken 1 h after shower, providing a standardized baseline for all individuals.
Study design and relationships between odor intensity, odor characteristics, age, and body sites. Dots mark odor intensity as shown on the left axis while bar-charts indicate the number of subjects as shown on the right axis. In addition to parent-assessed odor groups Additional file 2 : Table S2 , a single professional perfumer assessed odor intensity and character in all subjects, sites, and at all time points. In terms of odor characteristics, the underarm and neck regions were marked by sour and sulfur odors in the medium and high odor intensity ranges, respectively Fig.
In contrast, the head region was primarily characterized by a greasy odor, highlighting that different regions of the body are likely to have different microbial metabolism contributing to malodor. This property however seems to be specific to the underarm, and in the neck and head regions, sour odor is dominant at both time points in children and teenagers Fig.
These observations provide the essential backdrop for our analysis of microbial contributions to malodor in the following sections. Leveraging the metagenomic data for cross-kingdom analysis, we noted that different body sites exhibited different kingdom level distributions Additional file 1 : Figure S1. The increased abundance of viruses and eukaryotes in the head and neck regions is similar to what has been observed in nearby sites retroauricular crease, occiput in adults, indicative of the unique niches that they offer [ 18 ].
Specific microbiome signatures emerged for each body site at the bacterial species and genus level as well Additional file 1 : Figures S2, S3 , despite the presence of clear differences between the microbiomes of teenagers and children Fig. Similarly, while the increased presence of M. These differences correlate with changes in apocrine gland activity during puberty and can serve as the basis for differences in malodor characteristics between children and teenagers.
Additionally, all subjects had a much lower underarm abundance of Corynebacterium species than what has been observed in adults [ 9 ] suggesting that distinct species may play a role in malodor in these age groups.
Association between skin microbiome, odor intensity, age, and time of sampling. Data are represented as the mean relative abundance within a group. CAP analysis is based on the Bray-Curtis dissimilarity. Size of each dot represents the relative odor intensity score in each sample and the number overlapping each dot indicates samples collected before 1 or after 8 exercise. Canonical analysis of principal coordinates of variation of the skin microbiome in different body sites in relation to age group, gender, and timepoints 1 h or 8 h further illustrates the strength of associations between odor intensity, age, sampling time, and the skin microbiome Fig.
This pattern is also observed in the neck but is not significant on the head, where there is a stronger association with gender Additional file 1 : Figure S5. Microbiome composition in the head area is also unique in that it does not seem to shift noticeably after exercise. One possibility for this is the limited impact of a shower on the scalp microbiome compared to other sites, with microbes residing in the hair follicle making the scalp microbiome more stable and resilient.
In general, consistent trends were observed between the cross-sectional analysis and longitudinal analysis, where taxa that were positively correlated with malodor also increased in abundance after exercise Table 1.
For example, in the underarm, Staphylococcus epidermidis showed the strongest association with malodor when both age groups were jointly analyzed Additional file 1 : Figure S7, Table 1 , though the trend was consistently seen in each age group and in timepoints before and after exercise.
Interestingly, a Staphylococcus phage was also observed to be positively correlated with malodor, potentially driven by the association of its host species and highlighting the importance of phage-bacteria interactions on the skin [ 19 , 20 ]. This analysis further emphasizes the important role that Staphylococcus species play in malodor in children and delineates their specific contributions in different body sites and age groups [ 5 , 8 ].
A Cutibacterium species C. Other Cutibacterium species C. Corynebacterium species C. As Corynebacterium species are known to produce sulfur odorants [ 23 , 24 ], this observation could be a reflection of the fact that the underarm skin microbiome pre-puberty lacks the precursors from apocrine secretion to support their metabolism into a sulfurous malodor.
Interestingly, Acinetobacter species specifically A. The pathways involved in these species in mitigating malodor perception are unclear but one possible mechanism is through competition with other microbes via degradation of malodor precursors into aliphatic molecules [ 25 ].
In agreement with our earlier analysis Additional file 1 : Figure S5 , no microbes were found to be malodor-associated in the head area. Overall, these analyses highlight the varied microbial associations with body odor and that different distributions of key microbial factors and odor components across individuals, body sites, age groups, and timepoints may play a role in odor production. Notably, genus level analysis of the microbiome was unable to identify key associations in the underarm Additional file 1 : Table S3 , highlighting the importance of species differences and the strengths of shotgun metagenomic analysis for studying malodor-associated microbes.
In particular, our results highlight the dominant role that S. The transition through puberty leads to an increasingly sulfur dominated odor characteristic and shifts in Staphylococcus and Corynebacterium activity may contribute to this [ 5 ]. We further explore these relationships in the next section through analysis of malodor associated pathways in the skin microbiome.
This analysis showed that lactic acid was the most abundant precursor in children and teenagers followed by glycerol more abundant in teenagers , isoleucine, and leucine Additional file 1 : Table S4. Overall, children and teenagers revealed similar GCMS and GC-O profiles with teenagers being more abundant for the dominant compounds—acetic acid and isovaleric acid.
Based on this information, we then went on to do a functional analysis to discover malodor-associated genes and pathways in vivo and in a data-driven manner. Significantly associated genes were then aggregated in pathways to understand their contribution to the production of malodor-causing compounds.
Mapping the identified genes onto pathways, however, did not reveal consistent associations within a pathway e.
Particularly in the underarm, pyruvate metabolism and branched-chain amino acid metabolism pathways were enriched for genes in S. Enzymes derived from S. Lactic acid and glycerol are converted to pyruvate in the glycolysis pathway. In the presence of pyruvate, enzymes responsible for the biosynthesis and subsequently the degradation of leucine, valine, and isoleucine to yield the branched-chained fatty acid isovaleric acid e.
In an independent pathway, enzymes involved in oxidative degradation of pyruvate aliphatic carboxylates to acetyl-CoA Swanson Conversion in a process that is key to the production of acetic acid and sour odor were found to be malodor-associated in S. These results agree with previously reported in vitro studies [ 10 ]. Similar pathways were also associated with malodor in the neck, but this time, the associations were seen primarily with S. Pathways and enzymes associated with sour odor-producing compounds in the underarm.
Numbers in the bars indicate the number of KOs where the relative abundance is significantly correlated with odor intensity. Pathways and enzymes associated with sour odor-producing compounds in the neck. For the production of 3-methylsulfanylhexanol 3M3SH , which is associated with malodor with sulfur characteristics, we observed a positive association with both Staphylococcus species S. Previous in vitro observations have demonstrated the ability of S. Our metagenomic results indicate the presence of cystathionine beta-lyase in S.
Further in vitro experiments are needed to validate this possibility. In addition, our metagenomic data did not reveal the presence of Corynebacterium striatum and the aminoacylase enzyme agaA; in both children and teenagers which have been shown to mediate the production of HMHA [ 23 ]. This data indicates that these molecules are unlikely to be the main drivers of malodor in our cohorts, compared to their key role in adults [ 14 ].
While both the Staphylococcus species were able to produce significant quantities of acetic acid and isovaleric acid, other species found commonly on the skin such as C. These results highlight the primary role of Staphylococcus species in the production of acetic acid, isovaleric acid, and 3M3SH from odor precursors in sweat and in explaining the sour and sulfur odor characteristics observed in Asian children and teenagers.
Capability to transform precursors in sweat into malodor-associated compounds in different skin microbes. GCMS results from single bacterium inoculation for 24 h in sweat collected from subjects. Note that only S. The culture experiments were conducted under aerobic conditions. Malodor is a phenotype that is well known to arise from specific interactions between host-derived odor precursors and the microbial metabolism that they support [ 6 ].
In this respect, this study serves as an ideal test-bed for exploring analytical approaches to uncover host-microbiome metabolic interactions that define a phenotype of interest. While malodor in adults and Caucasian populations has been extensively studied [ 5 , 6 , 9 ], malodor in Asians and particularly in children and teenagers has not received commensurate attention. Our investigations show that it is indeed a problem of consumer interest that impacts the quality of life of affected children, suggesting that its influence on the psychological well-being of children deserves further research.
In designing a study to identify malodor associated microbial species and pathways, several aspects need to be considered, including the possibility that there might be taxa that are slow growing but strongly associated with malodor, while others may only generate malodor when they are sufficiently abundant.
Our design thus incorporated both longitudinal using exercise to generate sweat and odor precursors and cross-sectional aspects in multiple age groups to broadly capture different signals of association. Our data indicates that there are consistent signals from the longitudinal and cross-sectional analyses in most cases, except for Corynebacterium species and M. Additionally, the data in this study highlights different microbial contributors to body odor in different age groups and body sites, e.
This is despite the abundance of S. Prior work to study microbial contributions to axilla malodor has primarily emphasized the role of Corynebacterium species [ 7 ] in adults.
Using 16S rRNA sequencing, these studies have shown that Corynebacterium , Staphylococcus , and Cutibacterium species are the dominant bacteria in the axilla region [ 9 , 26 , 27 , 28 ].
Of these, Corynebacterium species were shown to be more abundant than Staphylococcus species in groups of individuals not using antiperspirants or deodorants [ 26 ]. Malodor in adult axilla was also typically found to be dominated by sulfur or rancid odor characteristics from 3M3SH, 3M2H, and HMHA generated mainly by Corynebacterium species [ 7 , 9 , 29 ]. In comparison, our study shows that Corynebacterium species are less abundant in children and teenagers and Staphylococcus species are more abundant.
This difference may be in part due to the axilla microenvironment in children and teenagers being shaped by eccrine secretion. While technical differences in metagenome profiling could also affect these comparisons, we note that shotgun metagenomics and 16S rRNA profiling have shown good concordance in a previous study [ 17 ].
In addition, sour odor was found to be more common in children in this study, and correspondingly, our analysis has highlighted the central role of Staphylococcus species in body odor in children.
Among Staphylococcus species, while most earlier studies have investigated the role of S. This has significant consequences in terms of interventions for malodor—while the main approach for adults uses antiperspirants to control malodor production by slow-growing Cornybacterium species, antimicrobials may be more appropriate for the fast-growing Staphylococcus species in children as antiperspirants have been observed to relatively enrich for them [ 26 ].
Additionally, as S. In pre-pubescent children, apocrine glands are not fully activated [ 12 ], and thus, eccrine-derived precursors could play a more significant role in the observed odor characteristics. Apocrine glands are comparatively more active in teenagers whose malodor profile is therefore expected to be more similar to adults. These expectations match with our observations of higher odor intensity in teenagers versus children and a switch to more sulfur characteristics in teenagers.
In addition, enzymes from different species that belong to the same enzyme class may have very different efficiencies and substrate specificities [ 35 ], e.
This problem is exemplified by a recent report showing that metagenomic pipelines can highlight very different functional pathways using the same dataset [ 36 ].
Enhanced clustering and assembly approaches enabled by advances in sequencing technology could help address these limitations in the future [ 37 , 38 ]. To our knowledge, this is the first report to describe taxa that are negatively correlated with malodor but their mechanism of action remains unclear. These associations could be due to various reasons including a the production of compounds that mask malodor or have lower odor intensity as proposed here for P.
Culture experiments with human sweat as performed here provided a unique framework to realistically model precursor availability and highlight the contribution of Staphylococcus species for odor generation. Further experiments with consortia of bacteria could help study interactions between them and thus identify mechanisms for malodor mitigation. Two groups of subjects were recruited for this study — 1 15 children consisting of 8 females and 7 males from 5 to 9 years old and 2 15 teenagers consisting of 8 females and 7 males from 15 to 18 years old.
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