A persistent body odor that smells distinctly of onions, garlic, or sulfur can be a source of significant personal concern. This noticeable aroma, known technically as bromhidrosis, signals the presence of specific volatile chemical compounds being released by the body. The source of this pungent scent is generally not a lack of hygiene, but rather a byproduct of internal metabolic processes or the natural interaction between skin secretions and the microscopic world living on the skin’s surface. Investigating the source of this odor requires looking closely at what the body takes in and how it processes certain molecules.
How Diet Contributes to Sulfur Odor
The most frequent source of a temporary, sulfurous body aroma comes from the foods people consume, especially those rich in organosulfur compounds. When foods like garlic, onions, leeks, and certain cruciferous vegetables are digested, they release potent sulfur-containing molecules into the bloodstream. These molecules are metabolic byproducts that the liver cannot fully break down into odorless compounds before they circulate.
Garlic, for instance, contains alliin, which converts into allicin when the clove is crushed or chopped. Allicin is then metabolized into various volatile sulfur compounds, including allyl methyl sulfide (AMS). AMS is particularly problematic because it has a very low odor threshold and is not rapidly metabolized by the body. Because it is oil-soluble, AMS is absorbed into the blood from the gastrointestinal tract, where it then circulates throughout the body.
This pungent compound is then excreted through multiple exit routes, including the lungs, which causes “garlic breath,” and through the skin via sweat and sebaceous glands. The process of excretion can last up to 24 hours until the body fully eliminates the compound. Similarly, other sulfur-rich foods like cabbage, broccoli, and red meat contain sulfur amino acids that can be broken down by gut bacteria into smaller, volatile molecules that may also be released through the skin.
The Science of Sweat and Bacterial Interaction
A different, more localized source of onion-like odor originates from the armpits and groin, where two types of sweat glands function differently. Eccrine glands are distributed across most of the body, producing sweat composed mainly of water and salt for temperature regulation, which is virtually odorless. In contrast, apocrine glands are concentrated in hairy areas and produce a thicker, oilier fluid rich in proteins, lipids, and steroids.
This apocrine sweat is initially odorless when it is secreted into the hair follicle. The characteristic pungent smell develops only when the sweat reaches the skin’s surface and is metabolized by the resident skin microbiota. Specific bacteria, primarily certain species of Corynebacterium and Staphylococcus, break down the odorless secretions into volatile organic compounds (VOCs).
The distinctive onion or sulfur odor is often caused by the bacterial cleavage of sulfur-containing precursors secreted in the apocrine sweat. For example, the bacterium Staphylococcus hominis is known to produce the thioalcohol 3-methyl-3-sulfanylhexan-1-ol (3M3SH), a volatile sulfur compound with a strong rotten onion or meat-like smell. Factors like hormonal changes, stress, and wearing non-breathable fabrics can intensify this bacterial activity, leading to a more pronounced odor.
When Odor Signals a Deeper Health Issue
While diet and microbial action account for most cases of sulfurous body odor, a persistent or sudden change in body scent can occasionally signal an underlying health issue. These conditions involve the body’s inability to properly metabolize or excrete certain compounds, leading to their release through the breath, urine, or sweat.
One rare genetic disorder is Trimethylaminuria (TMAU), often called “fish odor syndrome,” though the smell can sometimes be mistaken for rotten eggs or garbage. This condition results from a defect in the FMO3 enzyme, which is normally responsible for converting strong-smelling trimethylamine into an odorless compound. When this enzyme is deficient, trimethylamine builds up and is excreted through all bodily fluids.
More seriously, severe liver or kidney disease can also cause changes in body odor. The liver is responsible for filtering toxins, and when its function is impaired, sulfur-containing compounds like dimethyl sulfide can accumulate and be released on the breath. This condition, known as fetor hepaticus, is often described as smelling like rotten eggs and garlic.
Certain medications, such as some antibiotics (sulfa drugs) or high doses of supplements like B vitamins, may also cause the body to excrete sulfurous compounds, resulting in a temporary change in scent. Any sudden, severe, or persistent change in body odor that cannot be traced to diet or hygiene warrants consultation with a healthcare professional to rule out metabolic or organ dysfunction.