Sulfur-smelling sweat is almost always caused by bacteria on your skin breaking down compounds in your sweat into sulfur-containing molecules. Your sweat itself is actually odorless when it leaves the gland. The smell develops when specific bacteria, particularly Corynebacterium species living in your armpits and groin, digest proteins and fatty acids in sweat and release sulfur byproducts. Diet, clothing choices, and occasionally underlying health conditions can all intensify or trigger that distinctive rotten-egg or onion-like smell.
How Bacteria Create the Sulfur Smell
You have two types of sweat glands. Eccrine glands cover most of your body and produce the watery sweat that cools you down. Apocrine glands are concentrated in your armpits, groin, and around your nipples, and they release a thicker, protein-rich fluid. This apocrine sweat is the raw material bacteria feed on.
Corynebacterium and other skin bacteria carry a specialized enzyme that cleaves amino acid compounds in apocrine sweat. One of the key byproducts is a sulfur-containing molecule called 3-methyl-3-sulfanylhexan-1-ol. One form of this molecule smells like tropical fruit, but the other form, which is the one your armpit bacteria favor, smells like onion and sulfur. Other bacterial species on your skin, including Propionibacteria and Micrococcaceae, contribute to the overall odor profile but Corynebacterium is the primary driver of that sulfurous note.
This is why the smell is strongest in your armpits and groin: those are the areas with the highest density of apocrine glands and the warm, moist environment bacteria thrive in. If you’ve noticed the sulfur smell is worse on one side of your body or in one specific area, it’s likely because the bacterial population there is different or denser.
Foods That Make It Worse
What you eat can shift the chemical composition of your sweat significantly. Cruciferous vegetables like broccoli, cabbage, Brussels sprouts, and cauliflower are among the biggest culprits. These vegetables release sulfuric compounds during digestion, and those compounds get excreted through your sweat, breath, and gas. If you’ve recently increased your intake of these foods, that alone could explain a new sulfur smell.
Garlic and onions work similarly. They contain organosulfur compounds that your body metabolizes and then pushes out through your pores, sometimes for a day or two after a heavy meal. Red meat, eggs, and alcohol can also contribute, though their effect is typically less dramatic than cruciferous vegetables or alliums. The smell usually fades within 24 to 48 hours after you stop eating the offending food, which is a simple way to test whether diet is the cause.
Genetics Play a Role
Not everyone’s sweat produces the same amount of odor, and genetics are a major reason why. A gene called ABCC11 controls how much odor-producing material your apocrine glands secrete. A specific variant of this gene dramatically reduces both body odor and earwax production. Between 80% and 95% of East Asian populations carry this variant, which is why body odor is less common in those populations. Among people of European and African descent, only 0% to 3% carry it.
If you carry two copies of the standard version of this gene, your apocrine glands produce significantly more of the precursor compounds that bacteria convert into sulfurous odor. This is not something you can change, but it helps explain why some people struggle with body odor despite good hygiene while others barely need deodorant.
When It Signals a Health Problem
In most cases, sulfur-smelling sweat is a hygiene or diet issue. But certain medical conditions can produce sulfur-like odors that are worth knowing about.
Severe liver disease can cause a distinctive sweet, musty smell on the breath and in urine. This happens because the liver can no longer properly process methionine, an amino acid, leading to a buildup of sulfur compounds like dimethyl disulfide and methyl mercaptan. This smell, called foetor hepaticus, is a sign of advanced liver dysfunction and would typically come alongside other symptoms like jaundice, abdominal swelling, or persistent fatigue.
Kidney failure produces a different pattern: an ammonia-like or fishy odor from the buildup of waste products the kidneys can no longer filter. Diabetic ketoacidosis gives off a fruity, acetone-like smell rather than a sulfurous one, though people sometimes confuse the two. A rare genetic condition called cystinuria causes excess cystine (a sulfur-containing amino acid) in the urine, which can give it a rotten-egg smell, though this affects urine more than sweat and is usually caught because it causes kidney stones.
If the sulfur smell appeared suddenly, won’t go away despite hygiene changes, or comes with symptoms like unexplained weight loss, dark urine, yellowing skin, or persistent fatigue, it’s worth getting checked out. For the vast majority of people, though, the cause is much simpler.
Your Clothing Matters More Than You Think
Synthetic fabrics like polyester can retain up to three times more odor than natural fibers like cotton or wool. Polyester’s non-porous structure traps sweat and bacteria against your skin, creating a warm, sealed environment where odor-causing bacteria multiply rapidly. If you’ve noticed the sulfur smell is worse when you wear certain shirts or workout gear, the fabric is likely amplifying the problem.
Switching to cotton, merino wool, or other natural fibers allows better airflow and draws moisture away from your skin, which slows bacterial growth. If you prefer synthetic workout clothes, washing them with a sports-specific detergent or adding a cup of white vinegar to the wash can help break down the trapped odor molecules that regular detergent misses.
How to Reduce the Smell
Since bacteria are the root cause, the most effective approach targets them directly. Washing daily with antibacterial soap in your armpits and groin removes the bacterial colonies responsible for the smell. For a stronger approach, body washes or spot treatments containing benzoyl peroxide (commonly sold as acne washes like PanOxyl) are particularly effective at killing odor-causing bacteria on the skin. Apply it to your armpits for 30 seconds to a minute in the shower, then rinse.
Some people find success with diluted apple cider vinegar or lemon juice sprayed on the armpits. The acid lowers your skin’s pH, making it less hospitable to the bacteria that produce sulfur compounds. These work best as a supplement to, not a replacement for, regular washing.
On the dietary side, if you suspect food is the trigger, try cutting back on cruciferous vegetables, garlic, and onions for a week and see if the smell changes. You don’t need to eliminate them permanently. Just knowing the connection lets you plan around situations where you’d rather not smell like sulfur. Staying well hydrated also dilutes the concentration of odor compounds in your sweat, which can take the edge off.