Dented Cans and Botulism: How to Know What’s Safe

Food poisoning affects about 48 million people each year in the United States, but not all cases are the same. Most are mild and short-lived, while botulism is a rare but serious illness caused by a toxin that affects the nervous system and requires immediate medical treatment.

Dented cans often raise concern because damage can affect a can’s seal. However, most small dents are only cosmetic and do not make food unsafe. The important thing to know is which types of damage matter and which don’t.

What Is Botulism?

Botulism is a rare but sometimes life-threatening illness caused by toxins produced by the bacterium Clostridium botulinum. These toxins attack the nervous system and can lead to muscle weakness, paralysis, difficulty breathing and, in severe cases, death if not treated quickly.

What does a case look like in real life? Symptoms often start subtly with the same upset stomach and diarrhea common to food poisoning. But the disease can develop into more severe symptoms: blurred or double vision, drooping eyelids, slurred speech, difficulty swallowing or a dry mouth. From there, weakness and paralysis can spread through the body and may even affect the muscles needed to breathe, which is why botulism is considered a medical emergency.

One reason people associate botulism with canned food is that C. botulinum thrives in low-oxygen environments, like a sealed can. That might sound alarming, but properly processed commercial canning is designed specifically to prevent this. High heat destroys the bacteria and their spores, and the airtight seal keeps anything else from getting in after the contents are sterilized. When that system is intact, canned food is very safe.

Problems only come up when something interrupts that protection. What if a can is damaged after it’s sealed? Or, what if home canning isn’t done using safe methods? In those situations, bacteria may have a chance to grow and produce toxins.

The good news is that foodborne botulism is still very rare. Most canned foods you see on store shelves, even the dented ones, are safe. It comes down to knowing what to look for when a can isn’t perfect. This way, you won’t throw away good food while also preventing unnecessary risks.

How a Damaged Can Raises Botulism Risk

A dent, on its own, usually isn’t a problem. Most small, shallow dents are just cosmetic and don’t affect the food inside.

The concern starts when the damage is deep enough to affect the can’s seal, especially dents on the top or bottom seams or around the rim. These areas keep the can airtight, and even a small break can let bacteria in without any obvious visual signs.

If C. botulinum spores get inside, they can grow in low-oxygen, low-acid foods and produce a toxin that’s dangerous even in tiny amounts. The tricky part is that the food may still look, smell and taste completely normal.

Beyond botulism, a broken seal can also allow other harmful bacteria to get in, which is why food safety experts recommend tossing cans that are deeply dented, leaking, bulging, punctured or damaged along the seams. Unsure of what to do? Throw the can away. Better to be safe than sorry!

Which Dented Cans Are Dangerous?

Not all dented cans are unsafe. The real concern is whether any damage could ruin the can’s airtight seal.

Generally Safe: Minor Dents

Small, shallow dents on the side of the can are usually low risk, especially if the seams and rim are intact. These often happen during shipping and don’t affect the seal.

Look for:

Shallow dents (not deep or sharp)
Located on the flat side of the can
No creases, cracks or punctures
No leaking, bulging or rust

If the can only has a minor side dent and shows none of these warning signs, it's generally considered safe to use.

Unsafe: Deep Dents and Creases

Deep dents (especially those with sharp folds) can weaken the metal or damage the seal, even if the damage isn’t obvious.

Discard if:

You can press a fingertip into the dent
The metal is sharply creased or folded

When a dent is deep or sharply creased, it's safest to discard the can and choose an undamaged one instead.

Unsafe: Dents on Seams or Rim

Damage to the top or bottom seams is high risk because these areas form the airtight seal.

Throw away cans with dents on:

Top seam or lid edge
Bottom seam
Any seam connection points

Damage to the seam or rim is enough reason to throw away the can.

Unsafe: Bulging, Leaking or Punctured Cans

These are clear signs that the can is no longer sealed.

Discard cans that are:

Bulging or swollen
Leaking or sticky
Punctured, cracked or split

Never open or taste food from a can showing any of these signs. Discard it immediately.

Unsafe: Heavy Rust

Surface rust is usually harmless, but deep rust can weaken the can and create holes.

Avoid cans with:

Deep pitting or flaking rust
Rust near seams or seams you can’t clearly inspect
Any sign of structural weakening

When rust starts eating away at the can or appears around the seams, it’s time to choose a different product.

When in Doubt, Throw It Out

If you’re unsure whether a dent has compromised the seal, don’t risk it. The cost of replacing a can is small compared to the risk of botulism.

How to Inspect a Dented Can Before Using It

Before opening a dented can, take a moment to inspect it for signs of a damaged seal.

Check the Location of the Dent

A small dent on the side of the can is generally less concerning than one on the top, bottom or seams. Damage to the seams or rim is more likely to break the airtight seal, making the food unsafe.

Assess the Severity

Look closely at the dent. If it's deep, has a sharp crease or has folded the metal inward, discard the can.

Look for Warning Signs

Do not use the can if you notice any of the following:

Bulging or swollen ends
Leaks or dried food residue
Punctures or cracks
Heavy rust, especially around the seams
Damaged or split seams

These signs indicate the can is no longer airtight and should be thrown away.

Don't Rely on Smell or Taste

If the can appears safe and you open it, never taste the food to determine whether it's safe. Botulinum toxin cannot be seen, smelled or tasted, so contaminated food may appear completely normal.

Rule of thumb: If you're unsure whether a dent has damaged the can's seal, it's safest to throw the can away.

Foods at Higher Risk of Botulism

While any damaged can with a compromised seal should be discarded, some foods are more likely to support the growth of C. botulinum than others. These are typically low-acid foods, including:

Vegetables such as green beans, corn and asparagus
Meats and poultry
Seafood
Soups and stews
Gravy

High-acid foods, including most fruits, tomatoes and pickled products, are less hospitable environments for contamination. However, a damaged can should be thrown away regardless of its contents.

Symptoms of Botulism

Foodborne botulism symptoms usually develop within 12 to 36 hours after eating contaminated food, although they can appear as early as a few hours or as late as several days.

Because botulinum toxin is extremely potent, contaminated food cannot be made safe simply by cooking or reheating it. The bacteria and their toxins can remain serious health risks, making proper food handling, storage and prevention essential.

Stay Informed with StateFoodSafety

Understanding the risks of botulism is just one part of practicing safe food handling. Whether you're a home cook or a professional chef, keeping up with the latest food safety guidance can reduce the risk of foodborne illness.

Browse StateFoodSafety’s helpful library of resources and explore expert guides on food storage, foodborne pathogens, kitchen hygiene, temperature control and other topics that will increase your food safety knowledge.