That cheesy smell under your toenails comes from bacteria feeding on sweat and dead skin. The same type of bacteria used to ripen certain cheeses, called Brevibacterium, lives naturally on human skin and thrives in the warm, moist environment around your toes. As these bacteria break down sweat, they release sulfur-containing compounds called S-methyl thioesters, which produce that unmistakable pungent, cheese-like odor.
The Bacteria Behind the Smell
Your feet have roughly 250,000 sweat glands, more per square inch than anywhere else on your body. Sweat itself is mostly odorless. The smell happens when bacteria on your skin metabolize the sweat and dead skin cells that accumulate around and under your toenails. Brevibacterium is the primary culprit for the cheesy scent specifically, but it’s not working alone. Other bacteria produce isovaleric acid, the same compound responsible for the smell of Parmesan cheese and sweaty feet in general.
The space under your toenails is an ideal breeding ground. It’s dark, warm, and traps moisture along with tiny bits of dead skin, sock fibers, and other debris. All of that organic material gives bacteria a steady food source. When you scratch under a toenail and get a strong whiff, you’re smelling the concentrated byproducts of bacterial activity that’s been happening in a small, enclosed space.
Why Some People Have It Worse
Not everyone notices this to the same degree, and a few factors determine how strong the smell gets. Heavy sweating is the biggest one. People who sweat excessively from their feet (a condition called hyperhidrosis) create a much more hospitable environment for odor-producing bacteria. The more moisture, the more bacterial growth, and the stronger the smell.
Footwear plays a major role too. Shoes made from non-breathable materials like synthetic leather or plastic trap heat and moisture against your feet. Pairing those with cotton socks, which absorb sweat but dry slowly, creates ideal conditions for bacteria and fungus. If you spend long hours in closed-toe shoes, especially in warm weather or during physical activity, the bacterial population around your toenails has all day to multiply.
Nail length and shape also matter. Longer toenails catch more debris underneath. Thick or curved nails create deeper pockets where dead skin and bacteria collect. If you don’t regularly clean under your nails, that buildup becomes a concentrated source of odor.
When Smell Signals Something More Serious
A mild cheesy smell from otherwise healthy-looking toenails is normal and just a hygiene issue. But a sudden change in smell, especially if it becomes foul or rotten rather than just cheesy, can indicate a fungal or bacterial infection. Fungal toenail infections often cause the nail to thicken, turn yellow or brown, become brittle, and separate from the nail bed. The debris trapped under an infected nail tends to smell noticeably worse than typical bacterial byproducts.
If you notice any of these alongside the odor, you’re likely dealing with more than just bacteria on healthy skin:
- Discoloration: nails turning yellow, green, brown, or white
- Thickening or crumbling: nails that become unusually thick, brittle, or ragged
- Pain or tenderness: especially constant throbbing rather than just sensitivity to pressure
- Pus or discharge: yellow, white, or green drainage from around the nail, which points to bacterial infection
- Red streaking: lines of redness extending from the toe toward your foot, which can mean the infection is spreading
Warmth radiating from the toe or swelling that extends beyond the toe itself are also signs that an infection has progressed and needs professional attention.
How to Clean Under Your Toenails Properly
The American Podiatric Medical Association recommends gently running a wooden or rubber manicure stick under your nails to remove buildup. Avoid metal tools or anything sharp, which can puncture the skin underneath the nail and create an entry point for infection. Do this regularly, ideally every time you shower or bathe, when the nails are softer and debris loosens more easily.
After washing, dry your feet thoroughly. Pay special attention to the spaces between your toes, because any moisture left behind promotes bacterial and fungal growth. Trim your toenails straight across and keep them at a moderate length so there’s less space for debris to accumulate.
Reducing the Odor
A vinegar foot soak can help kill odor-causing bacteria. Mix one part vinegar to two parts warm water and soak your feet for 10 to 15 minutes. If that ratio doesn’t seem to make a difference, you can increase the concentration slightly. The evidence for vinegar soaks isn’t especially strong in clinical studies, but many people find them helpful for managing everyday foot odor, and the acidity does create an environment less friendly to bacteria.
Beyond soaks, daily habits make the biggest difference. Wash your feet with soap every day, not just letting shower water run over them. Rotate your shoes so each pair has at least 24 hours to dry out between wears. Choose socks made from moisture-wicking materials like merino wool or synthetic blends designed for athletic use, and change them if your feet get noticeably sweaty during the day. If breathable footwear isn’t an option for work, consider using an antifungal or antibacterial foot powder inside your shoes to absorb moisture.
For people who sweat heavily regardless of these measures, antiperspirant sprays formulated for feet can reduce moisture at the source. Applying them to clean, dry feet before putting on socks helps limit the sweat that bacteria need to produce those cheesy compounds. If excessive sweating persists despite these steps, a podiatrist or dermatologist can discuss stronger options tailored to your situation.