Underwear serves as a barrier between your body and outer clothing, and that simple layer does more health work than most people realize. It reduces friction against sensitive skin, absorbs moisture that would otherwise sit against the body and breed bacteria or yeast, and protects outer garments from bodily fluids. These functions sound basic, but when they fail, the consequences range from irritating rashes to shifts in the vaginal microbiome and, for men, measurable changes in sperm quality. The reasons for wearing underwear go well beyond social convention, and the type you choose matters more than you might expect.
Friction, Chafing, and Skin Breakdown
The groin, inner thighs, and buttocks are areas where skin folds press together and rub against each other with every step. Without a fabric barrier, the friction from outer clothing seams and rough textiles falls directly on some of the body’s most delicate skin. This constant rubbing, combined with the warm and moist environment of skin-on-skin contact, creates the perfect conditions for intertrigo, an inflammatory skin condition that develops where opposing skin surfaces meet. Intertrigo shows up as redness, rawness, and sometimes cracking, and it opens the door for secondary infections by Candida and other organisms.1Dove Press (Clin Cosmet Investig Dermatol). Recurrent candidal intertrigo: challenges and solutions Underwear helps by wicking sweat away from skin folds, reducing direct skin-to-skin contact, and providing a softer surface than most trouser fabrics.
This is not just a comfort issue. In nursing home populations, where residents may sit for long periods and have limited mobility, intertrigo affects roughly a third of residents.2PubMed. Prevalence and associations of xerosis cutis, incontinence-associated dermatitis, skin tears, pressure ulcers, and intertrigo in aged nursing home residents Proper undergarments and continence products are part of the clinical strategy for reducing that burden. For the average healthy person, underwear simply keeps the mechanical irritation from building up over the course of a day.
Vaginal Health and Fabric Choices
For women, the relationship between underwear and vaginal health is one of the most discussed topics in gynecology, and also one of the most misunderstood. The vagina maintains its own microbial balance, and anything that disrupts that environment can tip the scales toward infections like bacterial vaginosis or vulvovaginal candidiasis (yeast infections). Tight clothing that traps heat and moisture is a known risk factor. One study found that wearing tight jeans or trousers at least once a week was associated with a 50% higher risk of bacterial vaginosis compared to never wearing them.3PubMed. Risk factors for bacterial vaginosis Underwear made from breathable fabrics acts as a buffer, allowing some airflow and absorbing moisture rather than letting it pool against vulvar skin.
Cotton has long been the fabric gynecologists recommend, and there is evidence supporting that preference. Research into antimicrobial underwear has shown that cotton functionalized with certain compounds can reduce Candida albicans growth by about 87% and Candida parapsilosis by about 65%.4Textile Research Journal. Anti-candidiasis functional material for women’s cotton undergarments That research points toward medical-grade underwear as a future option, but even ordinary cotton underwear offers better moisture management than synthetic alternatives for most people.
A prospective study of women using antimicrobial underwear found that organisms commonly present at the start of the study, including C. albicans in about a third of participants, were either absent or substantially reduced after the intervention period.5PubMed Central. Effects of Antimicrobial Underwear on Vaginal Symptoms and Vaginal Microbiota: A Prospective Study This does not mean everyone needs specialty underwear, but it does confirm that what sits against vulvar skin affects the microbial community living there.
The Thong Myth
One persistent belief is that thong underwear causes urinary tract infections or vaginal infections by acting as a “bacterial highway” between the anus and the vagina. The logic sounds plausible, but the evidence does not back it up. A large survey study comparing nearly a thousand women found no significant difference in urogenital infection rates between thong wearers and non-thong wearers over the previous 12 months. Thong use was not an independent predictor of any urogenital infection.6PubMed Central. Brief versus Thong Hygiene in Obstetrics and Gynecology (B-THONG): A survey study If thongs were causing widespread infections, you would expect that kind of study to pick up a signal, and it did not.
That said, any underwear style that fits poorly, bunches up, or is made from non-breathable fabric can contribute to irritation. The issue is less about shape and more about fit and material. A well-fitting thong made from cotton is unlikely to cause problems for most people, while a poorly fitting brief made from synthetic material might.
Underwear and Male Fertility
The testes sit outside the body for a reason: sperm production works best at temperatures a few degrees below core body temperature. Anything that pushes scrotal temperature upward has the potential to affect sperm quality, and underwear fit is one variable that researchers have looked at closely.
Controlled measurements have shown that tight-fitting undergarments can raise scrotal temperature by roughly 1°C, and models that hold the testes closer to the body can push that increase to 1–2°C.7PubMed Central. Garment fit, scrotal thermoregulation, and male fertility outcomes: a narrative review That sounds small, but even modest thermal shifts may matter over time. A study of men attending a fertility center found that those who wore boxers most frequently had about 25% higher sperm concentration and 17% higher total sperm count compared to men who wore tighter styles. Boxer wearers also had about a third more total motile sperm and lower levels of follicle-stimulating hormone, which the body tends to ramp up when it detects lower sperm production.8Human Reproduction. Type of underwear worn and markers of testicular function among men attending a fertility center
The research has limits. These were men already seeking fertility help, so the findings may not generalize perfectly to the broader population. And the body’s hormonal feedback system partially compensated for the heat exposure, which means tight underwear probably does not render anyone infertile on its own. But for couples having trouble conceiving, switching to looser underwear is one of the simplest and cheapest changes a man can make. Some fertility specialists include it as standard advice.
Interestingly, while loose underwear appears better for sperm production, tighter-fitting underwear has a separate medical use. For men with chronic scrotal pain, clinicians sometimes recommend supportive, snug-fitting underwear or scrotal support to reduce the jarring and bouncing that aggravates the condition.9PubMed Central. A simplified treatment algorithm for chronic scrotal content pain syndrome The ideal underwear choice for men depends on what problem you are trying to solve.
Why Fabric Matters More Than You Think
The conversation about underwear fabric usually starts and ends with “wear cotton.” That is good advice, but the reasons are worth understanding. Synthetic fabrics like polyester do not just feel different; they create a different microbial environment against your skin. After exercise, polyester clothing harbors a distinct bacterial community compared to cotton. Micrococci, a group of bacteria strongly associated with body odor, grow preferentially on polyester and are mostly absent from cotton worn under the same conditions.10PubMed Central. Microbial odor profile of polyester and cotton clothes after a fitness session
Odor studies confirm the pattern. Polyester fabrics consistently rate higher in odor intensity than cotton or wool, and the difference is not about bacterial count. All fabric types carry similar numbers of bacteria after a day of wear, but the types of bacteria and how they interact with the fiber surface differ.11Textile Research Journal. Odor Intensity in Apparel Fabrics and the Link with Bacterial Populations Polyester’s smooth, hydrophobic fibers give odor-producing bacteria a surface they thrive on, while cotton’s absorbent, rougher fibers seem to favor a less odorous microbial mix.
This matters for underwear specifically because the groin is one of the body’s warmest, most moisture-rich areas. The microbial differences between fabrics are amplified in exactly these conditions. If you are prone to odor, irritation, or recurrent infections, switching from synthetic to cotton underwear is a low-cost experiment worth trying.
Allergic Reactions From Underwear
Some people develop itchy, red rashes in a band exactly where their underwear elastic sits. This is often dismissed as a heat rash or yeast infection, but it can actually be allergic contact dermatitis triggered by chemicals in the elastic or fabric dyes. Rubber accelerators used in elastic waistbands are a known source of contact allergies and can cause dermatitis right at the waistband line.12Annals of Allergy, Asthma & Immunology. Contact allergens for the allergist
The situation gets more interesting with laundering. A classic study identified six people who were allergic to their underwear elastic but tested negative to the raw rubber components and to brand-new elastic from the same supplier. The culprit turned out to be a chemical transformation that occurred when the elastic was washed with bleach. Sodium hypochlorite altered a rubber accelerator called zinc dibenzyldithiocarbamate, creating a new allergen that had not existed in the original garment.13PubMed. Allergic contact dermatitis to underwear elastic. Chemically transformed by laundry bleach If you develop a persistent rash at the waistband and switching brands does not help, the bleach in your laundry routine could be the actual trigger.
Textile dyes are another common offender. Dark-colored underwear is more likely to contain disperse dyes that can leach onto skin, particularly when combined with heat and moisture. People with known dye sensitivities are generally advised to choose light-colored, undyed underwear and to wash new garments before wearing them.
Underwear in Medical and Surgical Recovery
Hospitals have historically defaulted to loose gowns and generic garments for patients recovering from pelvic or urological surgery. But purpose-designed undergarments can make a real difference in post-surgical outcomes. A randomized trial of men recovering from posterior urethral surgery compared standard care to specially designed protective pants. The group wearing the functional underwear had significantly less scrotal swelling, fewer skin allergic blisters from dressings, fewer incidents of dressings falling off during walking, and less erection-related pain after surgery.14Scientific Reports. The nursing application of multifunctional protective pants after posterior urethral stricture surgery
This is a niche application, but it illustrates a broader point: underwear is not just a passive garment. When it is designed with specific body mechanics and medical needs in mind, it can reduce complications and speed recovery. Similar principles apply to compression garments used after hernia repair, cesarean delivery, and other abdominal procedures.
Compression Garments and Athletic Performance
Compression underwear and base layers are marketed heavily to athletes with claims about improved circulation, better thermoregulation, and enhanced performance. The evidence is less exciting than the advertising. Studies of compression garments worn during simulated team sport exercise found no thermoregulatory benefits and no detrimental effects on core temperature, physiological performance, or hydration levels. The only measurable difference was higher skin temperature in the areas covered by the garment.15Journal of Science and Medicine in Sport. Effects of wearing compression garments on thermoregulation during simulated team sport activity in temperate environmental conditions
Full-body compression garment testing confirmed the same pattern. Skin temperature under the garment was higher, but core temperature was unaffected, and time-trial performance was statistically the same with or without compression.16PubMed. Pressure and coverage effects of sporting compression garments on cardiovascular function, thermoregulatory function, and exercise performance Compression underwear may feel supportive and reduce the sensation of muscle oscillation during intense activity, which is why many athletes prefer them. But the physiological performance benefits appear to be mild at best. Where compression does help is in post-exercise recovery and in specific medical contexts like venous support, not during the exercise itself.
Incontinence and Skin Protection in Older Adults
For older adults dealing with urinary or fecal incontinence, the right undergarment is a medical necessity, not a preference. When skin is repeatedly exposed to urine or feces, the result is incontinence-associated dermatitis (IAD), a painful irritant skin condition characterized by redness, maceration, erosion, and frequent secondary infections.17PubMed Central. Incontinence-Associated Dermatitis in Older Adults: A Critical Review of Risk Factors, Prevention and Management About one in five nursing home residents is affected by IAD at any given time, and more than half of residents have two or more skin conditions simultaneously.2PubMed. Prevalence and associations of xerosis cutis, incontinence-associated dermatitis, skin tears, pressure ulcers, and intertrigo in aged nursing home residents
The risk factors for IAD include frequent episodes of incontinence (especially fecal), occlusive containment products that trap moisture against the skin, poor mobility, diminished cognitive awareness, and inability to perform personal hygiene.18Journal of Tissue Viability. A decade of research on Incontinence-Associated Dermatitis (IAD): Evidence, knowledge gaps and next steps Choosing incontinence underwear that pulls moisture away from the skin surface, combined with barrier creams and regular changing schedules, is one of the most effective prevention strategies. The garment itself becomes a frontline medical tool.
Diapers and Infant Skin
Diaper dermatitis, the clinical term for diaper rash, is one of the most common skin conditions in infancy. It develops when wet, soiled fabric sits against delicate skin for too long, raising the local pH and breaking down the skin’s protective barrier. Modern super-absorbent diapers have substantially reduced the problem by pulling moisture away from the skin surface and locking it into the absorbent core.19PubMed. Neonatal skin care: Developments in care to maintain neonatal barrier function and prevention of diaper dermatitis The principle is the same one that makes cotton underwear preferable for adults: keeping the skin surface dry prevents breakdown.
Cloth diapers, which have made a comeback for environmental reasons, require more vigilant changing because they lack the super-absorbent polymers that lock moisture away. Neither type is inherently harmful, but the management strategy differs. The undergarment’s job, whether it is a diaper or adult underwear, remains the same: manage moisture and minimize the time skin spends in contact with irritants.
Period Underwear and Menstrual Management
Period underwear has become a popular alternative to disposable pads and tampons, but the technology has trade-offs worth understanding. In a randomized trial comparing menstrual products, women using period underwear changed their garment about 3.5 times on their heaviest day, compared to 5.5 changes for disposable product users. Both period underwear and menstrual cup users reported a median of 3.5 leaks per heaviest day during the study period.20PubMed. Reusable menstrual hygiene products may lead to underdiagnosis of heavy menstrual bleeding: a randomised trial The lower change frequency is convenient, but researchers raised the concern that it could mask heavy menstrual bleeding. When you change a pad frequently, you get a rough sense of your flow. When the underwear absorbs everything and you change less often, abnormally heavy bleeding may go unnoticed.
Consumer research has also highlighted that many period underwear products still fall short on breathability, fabric resilience, and leakproof function, particularly in side-drain areas.21Advances in Social Science, Education and Humanities Research. Investigation and Analysis on Women’s Consumption Experience and Demand of Underwear During Menstruation The category is improving rapidly, but users should not assume that all period underwear provides the same level of protection. Testing a product on lighter days before relying on it for heavy flow is a practical first step.
Antimicrobial Fabrics and the Future of Underwear
Textile scientists are actively developing fabrics that go beyond passive moisture management and actively kill bacteria on contact. One approach involves embedding silver nanoparticles into cotton. Research on cellulose nanocomposites designed for children’s underwear found that silver-treated cotton achieved over 99.8% bacterial reduction against both Staphylococcus aureus and E. coli, and the antibacterial effect held up above 90% after 20 wash cycles. The treatment did not meaningfully change the fabric’s physical properties, and cytotoxicity testing showed it was safe for skin contact at the concentrations used.22PubMed. Antibacterial Cellulosic Nanocomposites Functionalized with Silver Nanoparticles for Children’s Underwear: Synthesis, Characterization, Physical Properties, and Cytotoxicity Assessment
Silver-treated textiles are already available commercially, though the durability and real-world performance of consumer products varies widely. Other approaches include copper-infused fibers and fabrics treated with antimicrobial peptides. The L-cysteine-functionalized cotton mentioned earlier in the context of vaginal health represents yet another path, targeting specific yeasts rather than bacteria broadly. Whether any of these technologies become standard for everyday underwear depends on cost, durability through repeated washing, and whether consumers feel the need for them. For people prone to recurrent infections or skin conditions, antimicrobial underwear may eventually become a genuinely useful tool rather than a marketing gimmick. For others, plain cotton washed regularly continues to work well enough.