Dented cans — no deal or no problem?

Botulism contamination is a horrifying possibility, but the risk may be nothing to fuss over

July 21, 2014
A home-canned product contaminated with botulism. Foodborne botulism affects roughly 20 people per year, yet I hesitate to open a dented can. [Image credit: Flickr user U.S. Department of Agriculture ]

It happens the same way every time.

I come home from a trip to the grocery store and begin putting the food away — a bag of grapes, a carton of mushrooms, half a gallon of milk — when suddenly, halfway to the pantry door, I look down at the can of tuna in my hand and notice a horrifying disfigurement: a dent.  My day instantly sours.

Dented cans have a long-established place in my list of personal neuroses.  My fear: the unlikely (but possible) risk of botulism contamination.  Botulism is a deadly illness caused by various strains of the Clostridium bacterium, most commonly Clostridium botulinum.  The bacteria has a strong affinity for low-oxygen environments (like cans and jars) and produces a neurotoxin that can cause victims to suffer increasing loss of muscle control. Gone untreated, the illness can spread from the face to the limbs, trunk and ultimately the respiratory system — resulting in death by suffocation. It’s a terrifying bacterium, every bit as nasty as its cousin Clostridium tetani, which causes tetanus.

My hesitation seems rational. Sure, most cans are processed with a pressure cooker that reaches temperatures high enough to kill off any adult bacteria and spores that might be present.  But improper canning happens — usually among people who can their own meats and veggies at home, although not always. In these instances, sneaky spores can inhabit the can, altering its shape and contaminating its contents. A can full of bacteria can appear swollen or misshapen. Additionally, the U.S. Department of Agriculture reports that deep dents — especially ones that create sharp edges or furrows in the metal — can damage the can’s seams allowing bacteria inside.

Yet even when I discover a dented can in my grocery bag, I often cringe at the thought of wasting what could be perfectly good food. So, before my latest hurt can of tuna got placed directly into the cabinet (where I’m pretty sure a dented can of refried beans I bought in January currently resides), I decided to figure out just how scared I should be about botulism contamination.

According to the Centers for Disease Control and Prevention, an average of just 145 cases of botulism are reported in the U.S. each year, equal to roughly 0.0000005 percent of the population. What’s more, just 15 percent of these are caused by foodborne bacteria. Even in the remote case of an infection, botulism doesn’t necessarily result in certain death — it can be treated at a hospital with antitoxins. These days, only about 3–5 percent of infected people die, although some will experience lingering effects like fatigue and shortness of breath for months or years afterward.

The misshapen cans in my cabinet are almost certainly the result of a bumpy trip home from the store, rather than multiplying bacteria — but it’s hard to shake that nagging paranoia. Yet armed with my new knowledge, I may break out the can opener tonight and finally dig into that dented can of refried beans. Bon appetít.

About the Author

Chelsea Harvey

Chelsea Harvey is a recent graduate of Auburn University, where she received a B.S. in zoology, as well as minors in English and Spanish. Unable to choose between her love of science and her love of writing, she spent most of her free time as an undergrad working for her campus newspaper while simultaneously memorizing hundreds of scientific names for class. Outside of SHERP, her interests include playing music with friends, traveling and keeping up with international affairs.



Joseph says:

Maybe the reason there so few cases is that people discard dented cans…

sabel says:

i worry most about rust, slight rust, slight discoloration that could lead to rust. how long until it is rust, rusts through, creates danger ,and does rust always lead to botulism?
i’ve trawled the internet and not found proper answers.
as someone with ocd this is really hard but i also can’t afford to throw out every second ca.

Rob says:

Unless the can is punctured or open in some other way,I have bigger things to worry about than the off chance of extremely remote poisoning and assume it was probably dropped.

Elliot says:

I work at a grocery store, and a woman handed me a can that was dented. She wanted a new one, so I asked why. I didn’t see anything wrong with it, so why should I send it to the damaged department? She told me very briefly about what botulism is. I thought she was nuts. Then I read this, and realized that she’s still nuts.

don says:

botulism is a toxin byproduct from a growing bacteria. A tin can only be contaminated at time of canning and if improper canning temperatures do not kill the bacteria. a puctured can will not develop botulism but will probably spoil. Botulism bacteria also do not survive exposed to oxygen which is why food left out will not develop it but other things might grow. Too bad so much false information is spread.

Dawn says:

I just opened a dented can of cat food and it exploded in my hands while opening it. I had to look down to make sure my fingers were still there. While I’ve always snickered about people not using dented cans, I never will again. Nor, will I use them ever again! FYI – the smell was horrific. I read this article and I am thinking that maybe, just maybe, it was contaminated with deadly bacteria!!! Yuck!!

Salty says:

Elliot, you work on a grocery store. Smile, exchange the can and get over yourself.

Daniel says:

I’m going to put the concern of botulism up there with the zombie apocalypse and super massive volcanoes.

Sandy says:

This is false information. Clostridium botulinum is an anaerobic bacteria and will not survive with oxygen (or foods high in acidity). Deeply Dented cans at the seams are likely to allow other types of bacteria to infiltrate the can and thrive, but not C. botulinum. So in order for someone to get botulism from canned foods, it would have meant that the can already had contained the bacteria to begin with, thus allowing the toxin to be formed in an anaerobic environment. DENTED CANS DO NOT CAUSE BOTULISM!!!!!

Lori says:

Sandy, while you are correct that C. botulinum does not thrive in oxygen and so would not, in its germinative state, enter through a dent in a can, that is not how C botulinum enters or exists in its dormant state. The bacterium that causes botulism, C. botulinum, exists as a spore and is ubiquitous in our environment, yes, our oxygen rich environment. The spore is tolerant of oxygen and is a dormant state of the organism. It is that which enters through a crack or dent or hole (OR pre-exists in the can, as you state – which is HIGHLY unlikely due to commercial treatment of foods for canning, though is a risk for home canned foods), and then, upon entering the oxygen free environment of the can, rich with food and water, it germinates and grows. So, dented cans do pose a risk for botulism. Other organisms that might enter only facilitate that process by consuming whatever small amounts of oxygen might be in the can. The same principles applies to getting tetanus from deep wounds – that is caused by the anaerobe C. tetani, a cousin to C. botulinum, an organism that also is ubiquitous in the environment in its spore form.

Jim says:

Lori- not sure I understand completely. I am no scientist, but it would seem that if a spore could enter a small crack or opening, then so can oxygen. So, wouldn’t that mean that it is no longer an oxygen free environment?

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