Sweaty pits can stink, sure — but what if the smell is clear-the-room bad?
It might surprise you to know that sweat itself is usually odorless, says Pauline J. Jose, MD, a specialist in family medicine and a member of the pH Labs health team, a nonprofit health information company. It's the bacterial breakdown of fatty acids and amino acids in sweat that gives it its tell-tale stink, she says.
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If things have gotten pretty stinky as of late, don't just slap on extra deodorant to cover your armpit smell and hope for the best; pay attention to this putrid perspiration.
"Changes in hormonal balance, metabolic disorders, bacterial skin infections and consumed food may have an impact on how much and what kind of sweat we produce," Dr. Jose says.
Smelly sweat has an official name: bromhidrosis, and it occurs mostly in the genital area, armpits and feet, Dr. Jose says. Your sweat can tell you a lot about your health. But if you're asking yourself: why does my sweat smell so bad, here are a few things to consider.
The Smell: Ammonia or Urine
The Culprit: A Protein-Rich Diet
Low-carb, high-protein or keto diets might be popular, but one weird side effect is that you might notice your sweat smelling like ammonia. (Urine can also have a strong ammonia odor. Meaning: You might instead think your sweat smells like urine.)
"Ammonia is a product of protein breakdown," Dr. Jose says. "It may help to reduce protein intake to alleviate ammonia-smelling sweat," she adds.
The Smell: Onions
The Culprit: Last Night's Dinner
Did you recently sit down to a garlic-y pasta dish? Or eat a stir-fry with lots of onions? These foods can affect the way sweat smells, Dr. Jose says.
So, if you think your sweat smells like garlic or onions, that curry dish you ordered last night might be the answer.
Some people also have bacteria hanging out in their pits that might make their sweat smell like fresh onion, according to January 2015 research in Microbiome. Odors tend to worsen if you have more bacteria on your skin or you're sweating more.
The Smell: Sour or Skunky
The Culprit: Your Skin Bacteria
"We all have our own microbiome, or bacteria that reside on our skin, specifically in areas like the armpit and groin," Dr. Jose says. "These bacteria dictate the smell sweat produces after it breaks down those sweat precursors."
If you're wondering why your sweat smells sour or like vinegar, you may have more of a specific bacteria, Corynebacterium, in your armpits, which produces putrid fatty acids, she explains.
Underarms tend to have more nasty compounds, including thiols, which smell like skunk, says Joe Schwarcz, PhD, director of McGill University's Office for Science and Society. (FYI, many people equate skunk with marijuana, so if you think your sweat smells like weed, there's a clue.)
The Smell: Fishy or Rotten
The Culprit: A Metabolic Disease
Foul-smelling body odors can also be indicative of a metabolic disease. These are rare, but one example is trimethylaminuria — aka "fish odor syndrome" — where the body is unable to breakdown trimethylamine, a compound found in certain foods. If you have this disorder, your sweat will smell like a rotten fish, according to the National Institutes of Health.
If you notice that your unpleasant body odor just isn’t going away, talk to your doctor about it, recommends Dr. Jose.
Is Someone Else Telling You That You Stink?
It might be their nose that's the problem.
In an older study, published in Nature in 2007, scientists determined that the breakdown of adrostenone, a steroid derived from testosterone, is recognized differently depending on one's odor perception. And apparently, whether or not someone thinks your sweat smells like urine or your sweat smells sweet like vanilla is all in their genes.
Fresh Fixes for Body Odor
The International Hyperhidrosis Foundation recommends the following when your BO is really stinky:
- Use an effective antiperspirant and deodorant (ask your doctor to recommend one if you haven't found one that works for you).
- Promptly change out of sweaty clothing.
- Wash the smelly area with antibacterial soap.
- Remove body hair (in places like the armpits) to control odor.
- Nature: “Genetic variation in a human odorant receptor alters odour perception”
- DermNet NZ: “Bromhidrosis”
- Microbiome: “Mapping axillary microbiota responsible for body odours using a culture-independent approach”
- McGill Office for Science and Society: “What am I smelling when I smell B.O.?”
- National Institutes of Health: “Trimethylaminuria”
- International Hyperhidrosis Foundation: “Bromhidrosis”
Is this an emergency? If you are experiencing serious medical symptoms, please see the National Library of Medicine’s list of signs you need emergency medical attention or call 911.