What It Means When Your Underarms Smell Like Onions

We've all been there before. Maybe when it happened to you, you were reaching up to get a water glass out of the cabinet. Or perhaps you noticed it after lovingly draping your arm across your friend's shoulder at the bar. Whatever the scenario, catching a whiff of your own body odor can be a little embarrassing. But why?

In modern society, body odor has been deemed as offensive — rude, even. As such, it has become the expectation that each of us are to remain fresh as a daisy at all times, without any room for error. But in reality, body odor is perfectly normal, and — just like pooping — it happens to all of us.

Like most things in life, normal body odor exists on a spectrum. While some people may emit a somewhat sweeter scent, others may give off a tangier, more pungent aroma (per the Cleveland Clinic). But if you've ever done a smell check only to discover that your underarms mimicked the familiar scent of onions, you may be wondering, "Is that normal?" Here's what we found out.

What makes sweat smell?

While it may be a little jarring to lift your arm and realize that you're the reason it smells like someone's chopping a pound of onions, body odor that smells like onions usually isn't anything to worry about. The American Society for Microbiology explains that, contrary to popular belief, sweat is essentially odorless. The smells we associate with body odor only occur once our sweat comes into contact with the microbiota that live in our skin. When those microorganisms metabolize our sweat, it's the byproducts of their feast that emits the foul smelling odor. These byproducts are referred to as volatile organic compounds (VOCs), and are commonly produced by bacteria in the Corynebacterium, Staphylococcus, and Cutibacterium genera families. 

If your armpits smell like onions, it's because of a sulfur-containing VOC called thioalcohols. 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. Alternatively, when your sweat is metabolized by some types of Corynebacterium, you may notice that you start to smell more like cumin. We each have an individual composition of microbiota on our skin, which results in a variety of different odors that still fall under a "normal" range. 

Causes of excessive body odor

In the event that the smell is particularly severe, however, onion-scented underarms could signal toward some kind of disorder. Bromhidrosis is a rare condition in which the apocrine glands — which are located in the axilla, genitals, and breasts — emit an excessively foul smelling odor (per Medscape). Bromhidrosis can go hand and hand with another disorder, called hyperhidrosis, which is characterized by excessive sweating. AARP explains that particularly potent smelling body odor has also been linked to diseases of the liver and kidneys, as well as hyperthyroidism.

If your underarms smell like onions, the Cleveland Clinic points out that you may also want to take a closer look at your diet. Foods like garlic and onions, as well as cabbage and cauliflower, contain higher levels of sulfur (per Hindustan Times). These sulfur-rich foods are chock full of VOCs, which can amplify the smell of your body odor.