A persistent smell around your butt usually comes down to one of three things: sweat mixing with bacteria, incomplete cleaning after bowel movements, or a skin condition in the fold between your cheeks. The area is a perfect storm for odor: it’s warm, enclosed, rarely exposed to air, and packed with sweat glands. In most cases, the cause is manageable once you identify it.
Why That Area Produces So Much Odor
Your body has two types of sweat glands. The ones across most of your skin produce thin, watery sweat that mostly just cools you down. But the perianal region is dense with a second type, called apocrine glands, which release a thicker, oilier sweat packed with fats and proteins. This sweat is essentially odorless when it first hits your skin. The smell starts when bacteria, particularly Corynebacterium species that thrive in warm folds, begin breaking those fats down into volatile compounds.
The chemical byproducts of that bacterial breakdown include short-chain fatty acids (responsible for cheesy, goat-like smells), ammonia (that sharp, urine-adjacent sting), and sulfur compounds that can smell like onions or cooked vegetables. Your butt crack checks every box these bacteria need to flourish: consistent warmth, minimal airflow, constant moisture, and a steady supply of oily sweat to feed on. The result is an area that generates odor faster and more intensely than almost anywhere else on your body.
Fecal Residue and Minor Leakage
Toilet paper alone isn’t especially effective at removing all traces of stool. Dry wiping can leave behind a thin film of fecal matter that bacteria continue to break down throughout the day. If you notice the smell is more fecal than musty, incomplete cleaning is a likely contributor. Water-based cleaning, whether from a bidet, a handheld sprayer, or even damp wipes, does a significantly better job of removing that residue. The Cleveland Clinic notes that water simply outperforms dry toilet paper at clearing trace fecal matter.
Beyond cleaning habits, some people experience minor stool or mucus leakage without realizing it. This is far more common than most people think. Research published in Gastroenterology found that roughly 8.3% of non-institutionalized U.S. adults experience some form of accidental bowel leakage at least once a month, including leakage of liquid stool (6.2%) or mucus (3.1%). Internal hemorrhoids can prevent the muscles around your anus from fully closing, allowing small amounts of stool or mucus to seep out. Rectal prolapse, where part of the rectum slides downward, causes the same incomplete seal. If you frequently notice staining on your underwear or a fecal smell that persists even after thorough washing, this kind of seepage may be the reason.
Skin Conditions That Cause Odor
The skin between your buttocks is a common site for intertrigo, an inflammatory condition triggered by friction, moisture, and heat in skin folds. It starts as redness on both sides of the fold and can progress to raw, weeping, or cracked skin. Once the skin barrier breaks down, secondary infections from yeast (especially Candida) or bacteria move in and make the smell significantly worse. If you notice redness, tenderness, or skin that looks macerated (whitish and soggy), intertrigo is worth considering.
Another possibility is erythrasma, a bacterial skin infection caused by Corynebacterium minutissimum. It tends to show up in warm, moist skin folds and presents as slightly discolored, scaly patches. Many people with erythrasma have no symptoms at all, or just mild itching, so the infection can go unnoticed for a long time. It’s frequently mistaken for a fungal infection. A doctor can distinguish it quickly using a Wood’s lamp: erythrasma glows a distinctive coral-red color under ultraviolet light, while fungal infections do not.
Diet and Body Chemistry
What you eat directly affects how your sweat and body odor smell, because certain food compounds are excreted through your skin. Sulfur-rich foods like garlic, onions, cruciferous vegetables (broccoli, cabbage, cauliflower), and red meat contain compounds that your body converts into volatile sulfur molecules. These get released through sweat glands, adding an oniony or cooked-vegetable smell to areas where apocrine glands are concentrated.
Choline, found in eggs, liver, and fish, gets converted by gut bacteria into trimethylamine, a compound with a strong fishy odor. Most people’s livers neutralize trimethylamine efficiently, but research has shown that after eating choline-rich foods, as many as 10% of people produced body odor noticeable at a social distance. High-protein diets can also raise ammonia levels in sweat, producing a sharper, more acrid smell. If you notice the odor shifts based on what you’ve been eating, your diet is likely a contributing factor.
Clothing Choices That Trap Odor
Fabric plays a bigger role than most people expect. Cotton underwear breathes well, which sounds ideal, but it absorbs moisture like a sponge and holds it against your skin. That creates a warm, damp environment where odor-causing bacteria multiply quickly. Polyester wicks moisture away from the skin and dries fast, but without proper ventilation design, it can trap heat. Bamboo viscose tends to perform well on both fronts: it’s breathable, soft, and doesn’t retain moisture the way cotton does.
If you’re prone to sweating, avoid 100% cotton underwear, especially during physical activity or in warm weather. Look for blends that wick moisture and dry quickly. Tight-fitting clothing that presses fabric deep into the fold between your cheeks increases friction, heat, and moisture retention, all of which accelerate odor production. Changing underwear after exercise or heavy sweating makes a noticeable difference.
Practical Steps to Reduce the Smell
Switching from dry toilet paper to water-based cleaning is the single most effective change for most people. A bidet attachment, portable bidet bottle, or even unscented wet wipes will remove fecal residue that dry paper leaves behind. When showering, wash the area with a gentle, unscented cleanser and dry thoroughly afterward. Moisture left in the fold feeds the exact bacteria you’re trying to control.
Wearing breathable, moisture-wicking underwear and changing it when it gets damp helps cut off the cycle of sweat accumulation and bacterial growth. Trimming (not necessarily removing) hair in the area can also reduce the surface area where sweat and bacteria collect. Some people find that applying a thin layer of body powder or an antiperspirant designed for skin folds helps keep the area dry throughout the day.
If you’ve addressed hygiene, clothing, and diet and the smell persists, or if you notice unexplained staining, skin changes, itching, or discharge, a medical cause like hemorrhoid-related seepage, intertrigo, or erythrasma is worth investigating. These are all common, treatable conditions that often go undiagnosed simply because people are reluctant to bring them up.