Men wear underwear for a handful of overlapping practical reasons: to reduce friction against sensitive skin, to provide a hygienic barrier between the body and outer clothing, to offer mechanical support during movement, and to manage moisture in an area that sweats heavily. None of these reasons are exotic, but each one solves a real physical problem that becomes obvious the moment underwear is absent. The specifics get more interesting when you dig into how fabric choice, fit, and even scrotal temperature regulation affect comfort, health, and fertility.
Friction, Chafing, and Skin Protection
The groin is where skin meets skin almost constantly. Inner thighs brush against each other and against the seams of trousers with every step. Without a fabric layer in between, the repeated rubbing creates friction burns, raw patches, and the kind of painful chafing that anyone who has walked a long distance in jeans without underwear can describe vividly. Underwear acts as a low-friction buffer. The fabric sits close to the body and moves with it, absorbing the slide that would otherwise happen between skin and rougher outer garments.
This is especially relevant during exercise, manual labor, or hot weather when sweat makes skin stickier. Wet skin actually has a higher coefficient of friction than dry skin, which is why chafing tends to get worse as you sweat more. A well-fitting pair of underwear keeps the worst contact zones separated and gives moisture somewhere to go other than pooling between skin surfaces.
There is also a straightforward protective element. Zippers, rivets, coarse denim, and stiff waistbands sit right next to some of the most nerve-dense, thin-skinned tissue on the body. A layer of soft knit fabric between that hardware and the genitals prevents pinching, snagging, and the occasional painful entrapment that emergency rooms do, in fact, see from time to time. The underwear layer is cheap insurance against a painful and embarrassing trip to urgent care.
The Hygiene Barrier
Your groin produces more sweat per square centimeter than most other parts of the body, rivaled only by the armpits and the soles of the feet. The region also harbors a dense population of bacteria and fungi that thrive in warm, moist environments. Underwear serves as a sacrificial layer: it absorbs sweat, skin cells, and trace amounts of urine or fecal bacteria before any of that reaches your trousers or shorts.
This matters for practical reasons beyond cleanliness. Outer clothing is harder and more expensive to wash frequently. Denim, wool trousers, and dress pants are not designed to be laundered after every wear. Underwear is. A daily change of underwear lets you extend the life and cleanliness of outer garments by capturing the biological output of a warm, active body in a garment that costs a few dollars and goes straight into the washing machine.
The antimicrobial angle is real, too. When bacteria feed on the lipids and proteins in sweat, they produce the compounds responsible for body odor. Trapping that process in a thin, washable layer keeps odor closer to the source and easier to manage. Some modern underwear fabrics incorporate antimicrobial treatments or naturally resistant fibers like merino wool, but even plain cotton does the basic job of containment.
Mechanical Support and Comfort
Male anatomy includes external genitalia that move independently of the body. During walking, running, sitting, or bending, unsupported testicles and penis shift, bounce, and occasionally get caught in uncomfortable positions. Underwear provides gentle compression that keeps everything closer to the body and reduces the distraction of constant readjustment.
The degree of support varies enormously by style. Briefs and boxer briefs hold the genitals firmly against the body, which most men find more comfortable during exercise or physical work. Loose boxers offer minimal support but more airflow. The choice often comes down to activity level: a man running a marathon and a man sitting at a desk all day have genuinely different support needs, and the underwear market reflects that with styles ranging from compression shorts to barely-there trunks.
Support also protects against minor testicular trauma. The testicles are sensitive to impact, and even everyday movements like sitting down hard on a bicycle seat or catching an accidental bump are less painful when there is a snug layer holding them in place rather than leaving them free to swing into the point of contact.
Moisture Management and Fabric Choice
Not all underwear handles sweat equally, and fabric choice has meaningful consequences for comfort. Cotton is the traditional default: soft, breathable, inexpensive, and comfortable when dry. The problem is that cotton absorbs moisture readily and holds onto it. Once saturated, cotton fabric clings to the skin, stays wet for a long time, and creates the damp environment where chafing and fungal infections thrive.
Synthetic fabrics like polyester and nylon have become popular in athletic and performance underwear precisely because they wick moisture away from the skin and dry quickly. Research on textile performance confirms that synthetic fibers transport sweat to the fabric’s outer surface, where it evaporates faster, while natural fibers tend to absorb moisture internally, leading to longer drying times and reduced comfort during physical activity.1Proceeding of Textile Engineering Research Symposium -TERS2025. Enhancing moisture wicking and drying rate in linen/cotton fabric using weft knitted structure This is why most running, hiking, and gym underwear is now made from synthetic blends or merino wool rather than pure cotton.
For everyday wear in a climate-controlled office, cotton works fine. For anyone who sweats heavily, exercises regularly, or lives in a humid climate, moisture-wicking synthetics or wool blends make a noticeable difference in how dry and comfortable the groin stays throughout the day. The practical takeaway is that fabric matters as much as fit for the hygiene and comfort functions underwear is supposed to serve.
Underwear Style and Scrotal Temperature
One of the more interesting intersections of underwear and health involves fertility. The testicles sit outside the body for a reason: sperm production works best at temperatures a few degrees below core body temperature. Anything that raises scrotal temperature for extended periods can, at least in theory, impair sperm quality. This is where underwear choice enters the fertility conversation.
A large study of men attending a fertility center found that those who most frequently wore boxers had roughly 25% higher sperm concentration and 17% higher total sperm count compared to men who typically wore tighter underwear like briefs or boxer briefs. The boxer wearers also had about 33% higher total motile sperm count. Hormonal markers supported the interpretation that tight underwear was causing mild thermal stress: men in tighter styles showed higher levels of follicle-stimulating hormone, consistent with the body compensating for reduced testicular output by ramping up the hormonal signal that drives sperm production.2Human Reproduction. Type of underwear worn and markers of testicular function among men attending a fertility center
That said, the picture is not as alarming as it sometimes sounds in headlines. An earlier experimental study had men wear athletic supporters that raised scrotal temperature by about 0.8 to 1 degree Celsius and found no significant changes in sperm concentration, motility, morphology, or function. The researchers concluded that the temperature increase from typical athletic support garments was not enough to meaningfully suppress sperm production in men with normal fertility.3PubMed. Effect of increased scrotal temperature on sperm production in normal men The distinction may lie in duration and baseline fertility: a modest temperature increase over a few weeks might not matter for a man with healthy sperm counts, but for someone already on the lower end of normal, even a small thermal insult could push numbers into a clinically relevant range.
Research on nocturnal scrotal cooling adds another dimension. A study of men with existing fertility problems found that the highest scrotal temperatures occurred during rest and sleep, not during physical activity, likely because lying still in bedding traps heat. When these men used a device that cooled the scrotum by about one degree Celsius at night for twelve weeks while also reducing other sources of genital heat, their sperm concentration and total output improved significantly.4PubMed. Improvement of semen quality by nocturnal scrotal cooling and moderate behavioural change to reduce genital heat stress in men with oligoasthenoteratozoospermia The practical implication is that for men actively trying to conceive, switching to looser underwear during the day and sleeping without restrictive clothing at night is a low-cost step that could help, especially if sperm quality is already compromised.
When Fit Works Against You
Underwear is supposed to be comfortable, but poorly chosen waistbands and overly tight fits can create problems that go beyond the groin. Research on waist-level compression shows that belts and tight waistbands increase pressure inside the abdomen, and that pressure can have downstream effects on the digestive system. A study using a standardized waist belt found that the belt increased pressure in the stomach by about 7 mmHg when fasting and 9 mmHg after a meal, and that acid reflux episodes roughly doubled with the belt on compared to without it. The reflux measured at sensors above the lower esophageal sphincter increased approximately eightfold.5PubMed. Abdominal Compression by Waist Belt Aggravates Gastroesophageal Reflux, Primarily by Impairing Esophageal Clearance
While underwear waistbands are not as constrictive as a cinched belt, the principle applies to any garment that squeezes the midsection. Tight elastic waistbands worn for hours can contribute to the same kind of intra-abdominal pressure increase, especially in men who carry weight around the middle. Separate research has confirmed that raised abdominal pressure from external compression can mechanically distort the junction between the stomach and esophagus, promoting acid creep into the lower sphincter even without full-blown reflux events.6PubMed. Disruption of the gastroesophageal junction by central obesity and waist belt: role of raised intra-abdominal pressure If you find yourself with unexplained heartburn or that sour post-meal feeling, a too-tight underwear waistband is worth investigating as a contributor, particularly if you are also wearing a belt over it.
Beyond reflux, overly tight underwear can restrict blood flow to the skin, leave red marks and pressure sores along the waistband and leg openings, and contribute to folliculitis by trapping sweat and bacteria against compressed skin. The fix is straightforward: underwear should stay in place without digging in. If the waistband leaves deep impressions in your skin at the end of the day, it is too tight or the elastic has degraded and the pair needs replacing.
Why Fit Varies So Much Between Brands
One frustration men encounter is that a size medium from one brand fits nothing like a size medium from another. This is not just sloppy manufacturing. The male lower torso varies considerably in proportions: hip width, thigh circumference, the distance between the waist and the crotch, and the prominence of the buttocks and front anatomy all differ across body types. Research on male body morphology for underwear design has used 3D body scanning to classify the male lower torso into multiple subtypes based on these measurements, finding that a single set of size labels does a poor job of accommodating the actual variation in how men are shaped.7ResearchGate. Research on the male lower torso for improving underwear design
In practice, this means that finding comfortable underwear sometimes requires trying several brands or styles rather than assuming your usual size will work everywhere. A man with a narrow waist and muscular thighs has fundamentally different fit needs from someone with a wider waist and slimmer legs, even if they both technically wear the same numerical size. The pouch, the leg opening, and the rise all matter independently, and most mass-market sizing only accounts for waist circumference. Some newer brands have started offering more granular sizing or different pouch configurations, which reflects a growing recognition that the one-size-fits-a-range approach leaves a lot of men in underwear that bunches, rides up, or compresses in the wrong places.
Going Commando and When It Makes Sense
Given all of these practical functions, is there ever a reason to skip underwear entirely? For some men, yes. Sleeping without underwear is one of the more evidence-supported cases. Since scrotal temperatures peak during rest, sleeping in loose pajamas or nothing allows better thermal regulation overnight. For men who are not concerned about fertility, the comfort argument is simpler: if you are not moving much and not wearing rough outer clothing, the barrier and support functions of underwear are less necessary.
During the day, going without underwear works better with some clothing than others. Soft athletic shorts with a built-in liner, for example, already provide a smooth inner layer, making underwear redundant and sometimes counterproductive by adding bulk and extra seams. Loose linen trousers in hot weather may also be more comfortable without an additional layer trapping heat. On the other hand, going commando in stiff denim, wool dress pants, or anything with an exposed zipper is asking for exactly the chafing and mechanical problems that underwear exists to prevent.
Cultural norms play a role too, of course. In many workplaces and social contexts, the visible outline of genitals through trousers without the smoothing layer of underwear is considered inappropriate. Underwear provides a cosmetic function by creating a more uniform silhouette under clothing. This is less about health and more about social expectation, but it is one of the reasons the garment has remained essentially universal in modern dress even as other undergarments have come and gone.
Fungal Infections and the Underwear Connection
Jock itch, the common name for tinea cruris, is a fungal infection that thrives in the warm, moist folds of the groin. Underwear is both part of the problem and part of the solution. Tight, non-breathable fabric that traps moisture creates an ideal environment for the dermatophyte fungi responsible for jock itch. But going without underwear does not necessarily help, because sweat then soaks into outer clothing that sits against the skin all day and is laundered less frequently.
The best approach, according to dermatological guidance, is to wear underwear made from moisture-wicking fabric, change it after heavy sweating, and avoid sitting in damp clothing for extended periods. Cotton underwear that has become sweat-soaked is arguably worse than no underwear at all, because it holds moisture against the skin for hours. Synthetics or merino wool that pull sweat away from the surface keep the skin drier and make fungal colonization less likely. For men prone to recurrent jock itch, switching fabric type is often more effective than any topical treatment at preventing flare-ups, because it addresses the underlying environmental cause rather than the symptom.