ACOG’s patient FAQ on vulvovaginal health advises: "Wear cotton underwear" and "Avoid wearing underwear made of synthetic materials" because cotton allows the vulvar skin to breathe and helps keep the area dry. The guidance explains that excess moisture and heat can promote irritation and infections, so breathable cotton is preferred to synthetic fabrics that may trap moisture.

The study compared odor formation on polyester and cotton T‑shirts worn during a standardized spinning session, followed by 28 hours incubation. A trained odor panel determined significant differences between polyester versus cotton fabrics for the hedonic value, the intensity, and five qualitative odor characteristics, with polyester clothing after the spinning session smelling significantly less pleasant, more intense, more musty, more ammonia, more strong, more sweaty and more sour. The authors found that enrichment of micrococci occurred on polyester and, in general, on synthetic clothing textiles, and note that cotton fibers consist mostly of cellulose with a high adsorbing capacity, so moisture and odors are adsorbed and less malodor is emitted, whereas synthetic fibers have a poor adsorbing capacity, favoring malodor development.

The authors note that "clothing textiles are not sterile and can harbor high bacterial counts as sweat and bacteria are transmitted from the skin." They investigated microbial growth in cotton and synthetic fabrics and found that "Micrococci were isolated in almost all synthetic shirts and were detected almost solely on synthetic shirts" while "Staphylococci were abundant on both cotton and synthetic fabrics" and "Corynebacteria were not enriched on any textile type." The study concludes that "the composition of clothing fibers promotes differential growth of textile microbes" and that polyester T‑shirts "smelled significantly less pleasant and more intense, compared to the cotton T‑shirts."

This PubMed record indexes the same study as the PMC full text. Its abstract states that polyester garments had a more unpleasant odor profile than cotton garments after exercise and that bacterial communities differed by textile type, with micrococci enriched on polyester.

This dermatology review states that textiles can influence skin microclimate by modifying heat and moisture transfer and that synthetic fibers such as polyester are generally less permeable to air and water vapor than natural fibers like cotton. It explains that poor breathability and reduced moisture transport may lead to increased humidity at the skin surface, promoting overgrowth of microorganisms and aggravating conditions such as intertrigo and irritant dermatitis, particularly in occluded areas under tight clothing.

The WHO fact sheet notes that factors such as poor hygiene and prolonged moisture in the genital area can facilitate overgrowth of bacteria and yeast, contributing to conditions like bacterial vaginosis and candidiasis. It explains that tight or non‑breathable clothing, which keeps the genital area warm and moist, is considered a behavioral risk factor for some genital infections, and advises choosing breathable fabrics and avoiding prolonged wearing of damp underwear.

In an in vitro growth experiment, the researchers reported that "the largest growth was noted on polyester textiles (1-log growth increase; up to 1.72 × 10^7 CFU per cm^2), whereas the largest inhibition was noted on fleece textiles." They state that "cotton textile indicated a growth for Propionibacterium, Staphylococcus, and Enhydrobacter spp., while practically no growth (or inhibition) was noted for Micrococcus and Corynebacterium spp." In contrast, "polyester textile was associated [with] the greatest growth for Propionibacterium, Enhydrobacter, and Micrococcus spp." and "of the seven tested textile types, micrococci were able to gain the highest abundance on polyester fabrics (up to 10^7 CFU per cm^2)."

The full-text article reiterates that after intensive exercise, "T-shirts were collected from 26 healthy individuals... and incubated for 28 h before analysis" and that "a trained odor panel determined significant differences between polyester versus cotton fabrics" with polyester shirts smelling "significantly less pleasant and more intense." It emphasizes that "micrococci were selectively enriched on polyester and wool" and that "no selective growth was found for micrococci on cotton textiles after 3 days," indicating that synthetic fibers, particularly polyester, can favor the growth of specific odor-associated bacteria when contaminated with sweat.

This study examined how fabric type affects microbial growth and adsorption of skin bacteria on cloth. It found that fabric properties can influence bacterial survival and adherence, supporting the broader claim that textile material affects how sweat-associated bacteria behave on fabric.

NIAMS notes that clothing made of rough, tight, or irritating materials can worsen skin symptoms, and that breathable fabrics are often recommended for comfort. This is indirect evidence about skin comfort rather than a direct comparison of underwear materials and bacteria.

This kind of textile research evaluates how underwear fabrics manage moisture and how that affects the skin microclimate. Findings in this literature generally show that fiber composition and fabric structure influence moisture retention, evaporation, and local skin conditions, which are relevant to sweat trapping.

Reuters has reported on studies showing that fabric type can affect odor and bacterial communities on clothing. Secondary reporting is useful here mainly as corroboration of primary textile-microbiology research, not as the main evidence for the underwear-specific claim.

Patient guidance from the Urology Care Foundation advises women to avoid tight‑fitting pants and synthetic underwear that can trap moisture in the genital area. It recommends wearing cotton underwear and loose‑fitting clothes to let air circulate and keep the area dry, stating that this helps reduce irritation and may lower the risk of urinary tract infections by minimizing conditions that favor bacterial growth around the urethra.

This experimental study compared bacterial adherence on several textile fabrics and found that "cotton fabric, with a rough surface, attracted more bacterial cells compared to the smooth polyester surface." Using FTIR spectroscopy and microscopy, the authors quantified adherence and concluded that surface roughness and fabric chemistry influence attachment, with cotton showing higher initial adherence of bacterial cells than polyester under their test conditions.

Mayo Clinic notes that bacterial vaginosis is associated with a disruption of the normal vaginal flora and that lifestyle factors such as using an intrauterine device, douching, or wearing tight clothing and non‑breathable underwear may contribute by increasing heat and moisture in the genital area. It advises women to wear cotton underwear and avoid clothing that traps sweat to help maintain a healthier environment for vaginal bacteria.

In discussing preventive measures for vulvovaginal candidiasis, the article states that women should avoid tight, synthetic clothing and non‑breathable underwear that retain heat and moisture in the vulvar area. It recommends loose, cotton underwear because cotton allows better air circulation and absorbs moisture away from the skin, helping to reduce the warm, damp conditions that favor yeast overgrowth.

CDC public-health materials commonly emphasize moisture-wicking and breathable clothing for exercise comfort, but they do not specifically establish that polyester underwear traps bacteria more than cotton underwear. This is only indirect contextual evidence about moisture management in apparel.

Choose 100% cotton. The best material for underwear is cotton: It is less likely to cause an allergic reaction than synthetic fabrics and it is breathable. Cotton underwear wicks away excess sweat and moisture that bacteria and yeast thrive on. The article also notes that synthetic panels or fabrics do not breathe like 100% cotton.

This review notes that "cotton and polyester fabrics, when worn, may serve as substrates for microbial growth due to retention of sweat and nutrients" and that untreated fabrics "can harbor bacteria responsible for odor and potential skin irritation." It explains that antimicrobial finishes are often applied to polyester and other synthetics "to reduce bacterial colonization" because these fabrics can otherwise permit survival and multiplication of microorganisms in moist conditions, especially in sportswear.

This review on textiles in healthcare environments explains that "microorganisms can survive and multiply on textile surfaces when moisture and organic matter are present" and that "fiber type, fabric construction, and finishing treatments influence microbial persistence." It notes that natural fibers like cotton are generally more absorbent, which can remove moisture from the skin, while synthetic fibers may retain surface moisture in certain constructions, potentially affecting microbial survival, although direct comparisons between underwear fabrics are not addressed.

Reporting on Callewaert et al.'s work, the article explains that "soiled polyester shirts wound up harboring more Micrococci bacteria, a type of odiferous germ, than cotton shirts" and that "pungent bacteria from our skin grow more readily on certain workout shirts, namely those made from synthetic textiles like polyester." After volunteers wore cotton or synthetic shirts during a spinning class and the shirts were stored for 28 hours, "an independent panel of odor connoisseurs judged that the polyester shirts stank worse than cotton-based ones." The piece also notes that in Petri dish tests "cotton grew very few smelly germs... while the microbes continued to swarm over polyester" and that "synthetic nylon was a great refuge for Propionibacterium acnes."

Summarizing gynecologists’ advice, the article states: "Cotton underwear is more breathable and less likely to trap moisture, which can reduce the risk of irritation and infection." It contrasts this with nylon: "Nylon underwear is less breathable and can trap heat and moisture close to the skin," noting that this warm, moist environment can favor yeast and bacteria. Doctors quoted in the piece consistently recommend cotton over synthetic underwear for everyday wear and for people prone to infections.

Mayo Clinic’s prevention tips include wearing "cotton underwear and avoid tight-fitting clothing" because "cotton underwear allows the genital area to stay dry and doesn't trap heat and moisture" while "nylon and other synthetic fabrics may trap moisture and create a favorable environment for yeast." The guidance reflects clinical experience that synthetic underwear can retain moisture against the skin, which may contribute to microbial overgrowth, though it does not quantify bacterial levels.

The article explains that **organic cotton** underwear is "highly breathable" and that "The natural fibers allow air to circulate freely around your body, which helps regulate temperature and prevent the buildup of moisture and heat." In contrast, it states that "**Nylon**, by contrast, creates a barrier that limits airflow. This reduced breathability can lead to increased sweating and potential discomfort, especially in warm weather or during physical activity." It adds that cotton "absorbs moisture readily" while once saturated it can stay damp and "potentially create an environment where bacteria might thrive if the underwear stays damp for extended periods," whereas nylon "excels at wicking sweat away" and drying quickly but is less breathable.

The article notes that polyester underwear is often criticized for its lack of breathability compared to natural fabrics like cotton, explaining that in warm environments or during vigorous activity "the synthetic fibers' ability to retain heat and moisture" can cause discomfort. It states that polyester is known for retaining odors more than natural fabrics, with synthetic fibers absorbing and holding onto sweat and bacteria, leading to persistent odors even after washing, and that poor moisture handling can aggravate skin irritation and promote bacterial build‑up.

The brand’s comparison states: "**Breathability:** Cotton, especially certified organic cotton, is a clear winner. It lets heat and moisture pass through, keeping you comfortable... In contrast, entirely synthetic underwear like nylon traps sweat and heat, building the perfect microclimate for bacteria." It further claims that "Nylon... isn’t about absorption; it traps sweat and heat, and can get swampy fast" and that cotton "soaks up what needs to be soaked up, keeping you feeling fresh," highlighting a view that synthetic nylon underwear holds sweat and favors bacterial growth compared with breathable cotton.

WAMA’s blog argues that "Nylon underwear isn’t breathable and it can trap your sweat and cause chafing which may lead to skin irritation." It states that "Although it is marketed as absorbent and quick-drying, nylon actually traps heat and moisture which can lead to anything from minor discomfort caused by swamp crotch to yeast infections (for women) and fertility issues (for men)." By contrast, "Cotton is often said to be the best material for underwear. It is lightweight and breathable," suggesting that cheap synthetic underwear fabrics trap sweat and moisture against the skin more than cotton does, potentially supporting bacterial or yeast growth.

ThirdLove’s fabric overview notes that cotton "holds the gold standard for softness and breathability" and "absorbs moisture well" making it comfortable for everyday wear. In contrast, for nylon it states: "On the downside, nylon does not allow skin to breathe as well as cotton underwear, so it tends to trap heat. The fiber can irritate those with sensitive skin." This directly supports the idea that nylon underwear is less breathable and more likely to trap heat and moisture against the skin compared with cotton.

This comparison notes that pure cotton underwear absorbs moisture but does not wick it away as efficiently as some performance fabrics, potentially leaving the skin feeling damp. In contrast, it describes polyester underwear as using synthetic fibers designed for high‑performance moisture wicking but also says polyester may lack the breathability of natural fibers, potentially causing overheating, and that polyester "tends to trap heat and moisture" and can retain odors, which may exacerbate skin problems for some people.

Clinical dermatology and gynecology texts commonly recommend breathable, absorbent cotton underwear for people with recurrent fungal or bacterial genital infections, noting that synthetic, non‑breathable fabrics can trap sweat and moisture against the skin. These sources emphasize that prolonged moisture and occlusion increase the risk of intertrigo, folliculitis, and vulvovaginal infections, and that choice of fabric (cotton versus polyester/nylon) is one modifiable factor in managing these conditions.

The comparison explains that "Cotton is king for breathability and natural comfort" and "lets your skin breathe" but "tends to absorb moisture rather than wick it away, which can leave you feeling damp" after sweating. It describes nylon as "engineered for durability and moisture management" that "wicks moisture away" and "dries quickly" yet acknowledges that "nylon can sometimes feel less breathable than cotton" and "tends to hold onto odors more than natural fibers," implying that synthetic nylon may support odor-causing bacteria if sweat and bacteria are not washed out promptly.

The blog claims that while polyester is marketed for moisture‑wicking properties, "on its own, polyester is not a water‑resistant fabric" and that "it traps moisture" unless blended with other synthetics and special finishes. It further states that polyester underwear does not allow airflow to let the genitals breathe, creating a warm, damp environment that is described as "the perfect breeding ground for bad bacteria," and suggests that this can lead to various infections.

This consumer‑oriented guide states that cotton’s natural fibers are highly breathable, promoting air circulation that helps regulate body temperature and reduce moisture buildup, making it suitable for warm climates and everyday wear. It contrasts this with polyester, saying that polyester’s breathability is limited and that it "tends to trap heat and moisture close to the body," which can lead to discomfort during exercise or in hot weather, and notes that cotton underwear is often preferred for sensitive skin because it is hypoallergenic and gentle.

In this patient discussion on vulvodynia, multiple commenters report that "Nylon in my experience doesn't breathe enough. I'll wear it for exercise but not all day, I end up feeling uncomfortable otherwise" and that solid nylon "doesn't breathe" unless in a mesh form. One user writes: "Pretty much every gyno I’ve gone to has said that cotton is better because it allows the tissue to ‘breathe’ enough that things like bacteria and yeast do not grow," echoing clinical advice that cotton underwear is preferred over synthetic nylon to reduce moisture and microbial overgrowth.