Is It Normal to Have a Smelly Bum?

Some degree of odor around the perianal area is completely normal and expected. The region is home to dense bacterial colonies, apocrine sweat glands, and the exit point of the digestive tract, all of which produce volatile compounds that carry a smell. What most people worry about is whether their particular level of odor is unusual or a sign of something wrong. In the vast majority of cases, a mild smell is just biology doing its thing, though a sudden change in intensity or character can sometimes point to a hygiene issue, a dietary shift, or, less commonly, a medical condition worth investigating.

Why That Area Smells in the First Place

The skin around the anus sits in a warm, enclosed fold that stays moist for much of the day. Those conditions are ideal for bacterial growth, and bacteria are the primary generators of body odor everywhere on the body. Resident bacterial flora break down sweat, skin cells, and trace amounts of fecal matter into smaller molecules, many of which are volatile and smelly. The same basic process that makes armpits smell operates in the perianal region, just with a different mix of bacteria and substrates. Research on body-odor mechanisms confirms that unpleasant smell from the skin is usually caused by odorants produced by resident bacterial flora, and that the specific composition of a person’s microbiota influences which odors dominate.¹

Apocrine glands, which are concentrated in the groin and perianal area, secrete a thicker fluid than ordinary sweat. That fluid is virtually odorless on its own, but it is rich in lipids and proteins that skin bacteria feast on. The byproducts of that feast include short-chain fatty acids and sulfur-containing compounds, both of which carry strong odors. Add in the proximity to fecal material, and there is simply more raw material for bacteria to convert into smelly molecules than almost anywhere else on the body.

How Diet Changes the Smell

What you eat has a direct effect on the volatile compounds that end up in your stool and, by extension, on the odor that lingers around the perianal area. High-sulfur foods like broccoli, cauliflower, garlic, eggs, and red meat tend to produce more hydrogen sulfide and other sulfur-based gases during digestion. Spicy foods, alcohol, and heavily processed meals can also shift the chemical profile of stool. Researchers studying fecal volatile organic compounds have found that dietary changes measurably alter the smell of feces and the chemical makeup of the colonic environment.²

Fiber intake matters too, though not in a simple more-is-better way. Soluble fiber feeds gut bacteria and can initially increase gas production, but a consistently high-fiber diet tends to promote a healthier bacterial balance that produces fewer foul-smelling byproducts over time. Conversely, a very low-fiber, high-fat diet can slow transit time through the colon, giving bacteria longer to ferment and producing stronger-smelling stool. If you have noticed a sudden change in perianal odor, the first place to look is at what you have been eating over the last few days.

Hygiene Practices That Help and Some That Backfire

Thorough but gentle cleaning after a bowel movement is the single most effective way to reduce perianal odor. Dry toilet paper alone does not always remove all residue, which is one reason bidets and wet cleansing have become popular. A gentle rinse with water after wiping can help, but the evidence on habitual bidet use is more nuanced than you might expect. A systematic review of bidet use and perianal conditions found that very frequent bidet use, more than once or twice a day, was associated with a modestly higher odds of developing perianal itching, particularly in men.³ The likely mechanism is that excessive washing strips away protective oils and disrupts the skin’s natural moisture barrier, leading to irritation that can paradoxically worsen odor by promoting bacterial overgrowth on damaged skin.

Moist toilet wipes are another common choice, but they carry their own risk. Some contain preservatives like methylchloroisothiazolinone and methylisothiazolinone, as well as fragrances and other chemicals that can cause allergic contact dermatitis in sensitive individuals.⁴ Inflamed, irritated skin weeps fluid and creates a better environment for odor-causing bacteria, so a product meant to improve cleanliness can end up making the smell worse if it triggers a reaction. If you use moist wipes and notice redness, itching, or a worsening smell, switching to plain water or fragrance-free alternatives is a reasonable first step.

The general principle is straightforward: clean gently, dry thoroughly, and avoid overwashing. Patting the area dry after washing rather than rubbing, wearing breathable cotton underwear, and changing underwear daily (or more often during heavy sweating) all help keep the bacterial population and its odor output in check. Tight synthetic fabrics trap heat and moisture, which accelerate bacterial activity.

When Odor Points to a Skin Condition

Persistent or worsening perianal odor sometimes traces back to a dermatological problem rather than simple hygiene. Perianal eczema is one of the more common culprits. When the skin around the anus becomes inflamed, it can weep fluid, crack, and create an environment where bacteria thrive in unusual concentrations. Studies comparing the microbiota of acute and chronic perianal eczema patients have found elevated levels of certain bacteria, with acute cases showing significantly higher concentrations of Staphylococcus in the affected area.⁵ That bacterial shift can produce a noticeable change in odor.

Fungal infections are another possibility, particularly in people who sweat heavily, have diabetes, or are overweight. The warm, moist environment of skin folds near the buttocks is hospitable to yeast, and a fungal overgrowth tends to produce a distinctive musty or sour smell. Hemorrhoids that prolapse or bleed can also generate odor, as blood and mucus on the skin surface feed bacterial colonies. And contact dermatitis from soaps, laundry detergent residues, or fragranced products applied to the area can set off a cycle of irritation and secondary infection that worsens smell.

Anal Fistulas and Other Proctological Issues

An anal fistula is a small tunnel that forms between the inside of the anal canal and the skin near the anus, usually as a result of an infected anal gland. Fistulas typically produce recurrent purulent discharge along with pain and itching around the anus.⁶ That discharge is distinctly foul-smelling and often stains underwear. If you notice a persistent, localized bad smell accompanied by drainage or a small lump near the anus, a fistula is worth considering, and it generally requires medical treatment rather than improved hygiene alone.

Perianal abscesses, which are essentially the precursors to many fistulas, also produce a strong odor from pus collecting under the skin. Pilonidal cysts, which form in the crease of the buttocks rather than right at the anus, can likewise drain foul-smelling fluid when they become infected. All of these conditions share the feature of a smell that is distinctly different from ordinary body odor: sharper, more pungent, and often accompanied by visible discharge or swelling.

Fecal Incontinence and Leakage

Even minor, barely noticeable leakage of stool can produce a persistent odor that is hard to manage with ordinary hygiene. Minor fecal incontinence is more common than most people realize, particularly after childbirth, in older adults, and in people with conditions affecting the pelvic floor. The leakage may be so slight that it only amounts to mucus or a small stain, but the bacterial load in even a trace amount of fecal material is enough to generate significant odor, especially in a warm, enclosed area.

Treatments range from pelvic floor exercises and dietary adjustments to medical procedures. One approach studied for minor cases involves injectable bulking agents that increase pressure in the anal sphincter. Research on this technique found it could reduce the severity of incontinence, though quality-of-life improvements were limited.⁷ The point for anyone dealing with persistent perianal odor is that minor leakage is an underdiagnosed cause, and it is worth mentioning to a doctor rather than assuming the smell is just something you have to live with.

Rare Metabolic Conditions

In uncommon cases, a persistent and unusually strong body odor, including around the buttocks, can stem from a metabolic disorder. Trimethylaminuria, sometimes called fish odor syndrome, is the best-known example. People with this condition lack sufficient activity of an enzyme needed to break down trimethylamine, a compound produced during the digestion of certain foods. Trimethylamine accumulates and is released through sweat, breath, and other secretions, producing a smell often described as resembling rotting fish.⁸ The odor is not confined to any one body part; it shows up in sweat, saliva, and other secretions across the body.⁹

Trimethylaminuria is rare enough that most people with a smelly bum do not have it. But if you have a pervasive fishy or ammonia-like odor that does not improve with any amount of washing and seems to come from multiple parts of your body, it is worth asking a doctor about. A urine test can confirm or rule it out. Dietary modifications, particularly reducing choline-rich foods like eggs, liver, and certain legumes, can significantly reduce the odor in people who do carry the condition. Other metabolic issues that can produce unusual body odors include liver disease and kidney dysfunction, both of which allow odorous compounds to build up in the body rather than being properly cleared.

When the Problem Is Perception, Not the Smell Itself

Some people are genuinely convinced they smell bad when, by any objective measure, they do not. This is a recognized condition called olfactory reference syndrome, in which a person becomes preoccupied with the belief that they emit a foul body odor. In studies of people with this condition, common perceived odor sources included the mouth, armpits, and genitals, and the types of smells they described most often included stool and garbage.¹⁰¹¹

This is not the same as being self-conscious about normal body odor. People with olfactory reference syndrome often engage in extensive checking behaviors, such as sniffing themselves repeatedly, asking others for reassurance, and overusing deodorants or cleansing products. The distress is real and can be socially disabling. If you are spending significant time worrying about perianal odor, have asked friends or partners who consistently say they cannot smell anything, and still cannot shake the belief, talking to a mental health professional familiar with this condition can be more useful than yet another round of specialized hygiene products.

How Body Odor Changes Across Life Stages

Body odor, including in the perianal region, is not static across a lifetime. Prepubescent children have a different skin microbiome than teenagers, and the shift at puberty brings a well-documented increase in odor intensity. Research comparing the skin bacteria of children and teenagers found that specific bacterial species associated with stronger odors, particularly those producing short-chain fatty acids and sulfur compounds, become more abundant during and after puberty.¹² This applies across the body, including areas with apocrine glands near the buttocks.

Hormonal changes during pregnancy and menopause can also shift body odor. Pregnancy increases blood volume, alters sweat composition, and changes the gut microbiome, all of which can affect how the perianal area smells. Menopause brings changes in skin thickness and moisture, which can alter the local bacterial environment. Older adults often experience changes in bowel habits, pelvic floor strength, and skin integrity that can all contribute to increased perianal odor. None of these shifts are abnormal in themselves; they are simply part of how the body changes over time.

Practical Steps for Managing Normal Odor

For the majority of people whose perianal odor is normal but unwelcome, the solutions are straightforward:

• Gentle washing: Clean the area with water and a mild, fragrance-free cleanser once daily. Avoid scrubbing or using harsh soaps, which can strip protective oils and worsen the problem.
• Thorough drying: Moisture is the main accelerator of bacterial odor production. Pat dry completely after washing or using the toilet.
• Breathable clothing: Cotton underwear and loose-fitting pants allow air circulation and reduce trapped heat and sweat.
• Dietary awareness: If you notice a change in odor, review your recent diet. High-sulfur foods, alcohol, and artificial sweeteners are common culprits.
• Barrier creams: A thin layer of zinc oxide cream can protect irritated skin and reduce moisture, which indirectly limits bacterial odor.

For people who have had bowel surgery or conditions that produce unusually strong stool odor, bismuth subgallate is sometimes used to reduce the smell. A randomized trial in patients with complaints of smelly stools after a specific type of bariatric surgery found that bismuth subgallate treatment produced significant improvements in digestive symptom scores.¹³ This is a niche intervention, not something most people need, but it illustrates that options exist for cases where odor is genuinely disruptive.

The Evolutionary Backstory of Perianal Scent

It is easy to think of perianal odor as purely a hygiene failure, but the evolutionary picture complicates that framing. In most mammals, the perianal region is an active communication hub. Anal sac glands in dogs, for example, produce secretions whose odor profiles are unique to the individual, and research has shown that the proteins involved in releasing and detecting these scent signals are shared across a wide range of placental mammals.¹⁴ Humans no longer have functional anal sacs, but we retain apocrine glands in the region that are evolutionary remnants of this chemical signaling system.

The apocrine glands in the human perianal area are thought to be vestiges of a scent-signaling apparatus that was once used for individual identification, territorial marking, or reproductive signaling. In modern life, those glands still secrete, and bacteria still process those secretions into volatile compounds. The result is an odor that your nose is actually quite sensitive to, because detecting such signals in other individuals was once biologically useful. So the fact that you can smell your own perianal area is partly a story about your nose being tuned to pick up exactly those kinds of compounds, not necessarily a story about something being wrong.

Red Flags That Warrant a Doctor Visit

Most perianal odor is managed with the basics outlined above. But certain patterns deserve professional attention rather than another trip to the drugstore hygiene aisle:

• Discharge: Any persistent drainage of pus, mucus, or blood from near the anus suggests a fistula, abscess, or other structural issue that needs evaluation.
• Sudden dramatic change: A sharp shift in odor character, especially if accompanied by changes in bowel habits, weight loss, or abdominal pain, can sometimes signal gastrointestinal conditions including inflammatory bowel disease.
• Odor despite meticulous hygiene: If thorough, consistent cleaning makes no difference, the source may be internal (leakage, a metabolic issue) rather than surface-level.
• Persistent itching or rash: Ongoing pruritus ani combined with odor may indicate eczema, fungal infection, or an allergic reaction to a hygiene product.
• Whole-body odor: If the smell is not limited to the perianal area and shows up in sweat, breath, or urine, a metabolic screening is reasonable.

The conditions behind these red flags are all treatable, and most are straightforward to diagnose with a physical exam and, in some cases, a swab or blood test. The reluctance many people feel about discussing perianal odor with a doctor is understandable but worth pushing past, because clinicians see these issues frequently and effective solutions exist for nearly all of them.