Body odors that smell like onions are usually nothing to be concerned about. While it may be jarring to lift your arm and realize that you’re the reason for the smell, body odor that smells like onions is usually nothing to worry about. American Society for Microbiology Explains that sweat, contrary to what is commonly believed, has no odor. When our sweat is in contact with microbes that reside on our skin, we smell the odors. These microorganisms produce the foul-smelling smell when they metabolize the sweat. The byproducts of this process are called volatile organic compounds (VOCs) and they are produced most commonly by the Corynebacterium family, Staphylococcus and Cutibacterium families.
It’s probably a VOC containing sulfur called thioalcohols that is causing your armpits to smell of onions. When your sweat is consumed by Staphylococcus hominis bacteria, it produces 3-methyl-3-sulfanylhexan-1-ol (3M3SH), a thioalcohol that smells quite like rotten onions. You may also notice that your body starts to smell like cumin when you sweat is being metabolized. Our skin has an individual microbiota composition, resulting in various odors.