Can You Trust the Smell Test? What Your Nose Catches and What It Misses

Opening the container and sniffing is how most people decide whether food is still good. The sniff answers one question well: has this food spoiled? It answers a different question badly: will this make me ill? Those are two different groups of microbes, and your nose is only built to notice one of them.

What is happening

Spoilage and food poisoning are different organisms. Spoilage microbes produce the sour smell, the slime and the fizz — the signals the nose is good at. The bacteria that cause food poisoning generally do not change the taste, smell or appearance of food (USDA). So food can smell perfect and carry Salmonella or a toxin, and food can smell unpleasant and merely be past its best.

Tasting a little does not help. The dose of Staphylococcus aureus toxin that causes illness is less than a microgram, and the toxin survives heat (FDA). There is nothing to taste, and a "small bite" is not a small dose.

Cold does not stop everything. Listeria can grow at fridge temperatures (FSA, FDA) without changing how food smells.

Where the senses do work. The UK Food Standards Agency separates two kinds of date. "Best before" is about quality: you can smell the food, look for mould and check the texture, and it can be eaten after the date. "Use by" is about safety: the sniff test is not safe for any food with a use-by date, because you cannot smell the bugs that cause food poisoning (FSA). More on the labels: expiry vs best-before dates.

What to do

• Use-by food and cooked leftovers: go by the date and the clock, not the nose. Do not eat meat after its use-by date (FSA). For leftovers, count days from cooking; limits by country are in how to reheat leftovers.
• Best-before food: look and smell. Dry goods, tins and many dairy products past best-before can be eaten if they were stored as the label says, are within any "use within N days of opening" instruction, and show no mould and no change in smell or texture (FSA).
• Mould — the US and the UK draw the line differently.
  • US (USDA): on hard cheeses such as cheddar and parmesan, cut off at least 2.5 cm (1 inch) around and below the spot; soft cheeses such as brie with mould that is not part of the cheese go in the bin, because mould and bacteria can spread through them unseen.
  • UK (FSA): food that is obviously rotten or mouldy should not be eaten; cutting away a large margin might remove hidden toxins, but there is no guarantee — especially for children, pregnant people, people over 65 and anyone with a weakened immune system.
• Eggs: the float test shows age, not safety (FSA). An egg floats because air gets in as it ages; it cannot show which bacteria are inside. UK advice: eggs are fine for a couple of days after best-before if cooked thoroughly (FSA).
• Tins: judge the can, not the smell. Do not eat from a visibly bulging can; a can that spurts when opened may have gas from microbial growth. Shallow dents are usually fine; deep dents or rust are not (FSA).

When it is different

• A bad smell is still a good reason to bin food. The nose is right about spoilage; you do not need a safety argument to throw away food that smells off.
• Food left out is not judged by smell at all: see food left out overnight. Rice is the clearest example — its toxin has no smell and survives reheating: leftover rice and pasta.
• Pregnancy, older age, young children, a weakened immune system. Listeria hits these groups hardest (FDA), and the FSA's mould advice is stricter for them. Follow dates strictly rather than trusting the nose.

Sources

• USDA FSIS — Refrigeration and food safety
• USDA FSIS — Molds on food: are they dangerous?
• Food Standards Agency — Home food fact checker
• Food Standards Agency — How to chill, freeze and defrost food safely
• FDA — Bad Bug Book, 2nd edition

Checked: 23 September 2026