Canned foods are made through the canning process, which preserves and extends the shelf life of many foods, including meats, fish, vegetables, and fruits.

You can purchase canned foods online or in-store from commercial brands, but in some cultures, home-canning is a popular practice.

However, many people have concerns about the health and safety of some canned foods, including their potential to harbor harmful diseases like botulism — a severe and potentially life-threatening illness.

This article explains everything you need to know about botulism and the risks associated with canned foods.

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Botulism is a severe illness caused by toxins produced predominantly by the bacterium Clostridium botulinum, but also by strains of the Clostridium baratii and Clostridium butyricum bacteria (1, 2, 3).

These toxins are referred to as botulinum neurotoxins (BoNT) because they harm the nervous system, often leading to various forms of paralysis (1, 2, 3).

Therefore, although this illness is rare — with approximately 475 cases reported each year in the United States, Canada, and Europe — it is a serious and life-threatening public health concern (4).

There are several types of botulism (2, 3, 4, 5):

  • Foodborne botulism: infection caused by consuming foods contaminated with botulinum neurotoxins
  • Intestinal colonization: bacteria enter the body and produce the neurotoxins while they live in the gut
  • Wound botulism: a wound or damaged or cracked skin becomes infected with the bacteria that produce botulinum neurotoxins
  • Iatrogenic botulism: infections caused by high concentrations of cosmetic or therapeutic injections of the toxin, for example, botox injections
  • Inhalation botulism: inhalation of botulinum toxins through accidental or biologic warfare release

Of these, foodborne botulism (or food poisoning) is the most common cause of botulism and will be the primary focus of this article.

The strains of bacteria responsible for producing botulinum toxins grow ideally in anaerobic (low-oxygen) settings with low acidity, a low amount of salt and water, and a storage temperature between 37–98 ℉ (3–37 ℃) (6).

Thus, canned foods provide an ideal environment for bacterial growth.

Summary

Botulism is a rare but severe illness caused by toxins produced by the bacterium Clostridium botulinum. It may cause various forms of paralysis. Foodborne botulism, or food poisoning, is the most common cause.

The signs and symptoms of botulism develop over the course of a few hours to days, depending on the amount of toxin consumed from the contaminated food (5).

For example, a 35-year review of botulism cases in Turkey determined that symptoms developed 26.9 hours after patients were first exposed to the toxin (7).

Other research shows that symptoms typically developed after 12–48 hours, but in some rare instances, symptoms did not appear until 10–15 days after exposure to the toxin (8).

This delay in onset of symptoms, along with mild symptoms that are often present in other foodborne illnesses, make it difficult to diagnose botulism (8).

The botulinum neurotoxins disrupt the nervous system, which is responsible for many of the symptoms developed.

Symptoms of botulism may be mild but progress in severity if left untreated and can cause gastrointestinal and visual symptoms as well as forms of paralysis, including (2, 3, 6):

  • dry mouth (xerostomia)
  • nausea or vomiting
  • constipation or diarrhea
  • abdominal pain
  • double vision or blurred vision
  • drooping eyelids
  • headaches
  • facial palsy
  • slurred speech
  • dysphagia (difficulty swallowing) and choking
  • urinary retention
  • limb paralysis
  • respiratory failure

A combination of the severe symptoms may lead to coma and death.

Treatment may involve intubation and intensive care unit (ICU) support as needed, plus the administration of an anti-toxin, which is shown to be effective up to 24 hours after symptoms develop (9).

Summary

The symptoms of botulism develop over the course of hours to days, and they range from mild to severe depending on the amount of toxin exposure. Left untreated, symptoms worsen and may lead to coma and death.

Generally, about 80% of foodborne botulism can be attributed to home-canned foods (2).

For instance, of the 466 cases of botulism in Italy between the years 1986–2015, 90% (421 cases) were caused by foodborne botulism, most of which were linked to improperly home-canned foods (2).

Likewise, almost all of the 8614 cases of botulism in Ukraine between 1955–2018 were caused by homemade canned goods, with few cases attributed to commercial canned products (10).

High cases of botulism caused by homemade canned foods were also observed in reviews of botulism cases in The Republic of Georgia, France, and Iran (3, 6, 11).

Common home-canned foods that were linked to botulism cases in several countries include (2, 3, 11):

  • vegetables canned in oil and brine/water (mushrooms, olives, turnips tops, leafy veggies, peppers)
  • home-bottled and salted fish, smoked fish (tuna)
  • home-cured meat (ham, pork blood sausage, salami/sausages)
  • tofu and seitan

Less frequently, some commercial canned products, including green olives, canned fish, vegetables, and fruits, were linked to botulism cases. Unpasteurized commercial dairy products are also high-risk foods for botulism (2, 11, 12).

Summary

Most of the botulism cases due to canned foods are associated with homemade canned or bottled vegetables, meat, and fish. Commercially canned olives, fish, and fruits are linked to fewer botulism cases.

In some cultures, home-canning is a common practice to preserve access to foods during the off-season.

For instance, in the Republic of Georgia, many people can vegetables during the summer for use during the winter when food prices may be higher (6).

Practice safe home canning by (6):

  • Blanch vegetables before canning, or add boiling water to vegetables in the jar before sealing.
  • Do not add salt, vinegar, or uncooked vegetables during canning.
  • Adding garlic is shown to reduce botulism risk.
  • Use home-canned foods within six months.

Practicing safe home-canning more frequently — producing more than 57 jars per year — was also linked to a reduced risk of botulism (6).

Summary

Canned food safety is important to reduce the risk of botulism. Be sure that you can identify signs of contamination, and brush up on how to safely practice home-canning.

Here are some questions people often ask about canned food and botulism.

Can cooking kill botulism?

Unfortunately, bacterial spores that are able to grow in canned environments produce toxins that survive standard cooking methods, where food is not heated above 212 ℉ (100 ℃) (11).

Therefore, standard cooking does not simply kill botulism-causing bacterial spores, but botulism may be prevented by pressure-cooking, sterilizing your cooking and canning equipment, and using safe food hygiene practices (4, 6, 11).

Commercially, ionizing radiation deactivates bacterial spores (4).

Can you detect botulism in canned foods?

According to the Centers for Disease Control and Prevention (CDC), homemade and store-bought canned foods can be inspected for contamination (13).

Discard the canned food if any of these conditions exist (13):

  • the can is leaking, swollen, or has bulges
  • the can looks damaged or cracked
  • liquid or foam spurts from the can when opened
  • the food inside is moldy, smells bad, or is discolored

Can you get botulism from smelling or touching contaminated food?

The botulism toxins cannot be absorbed through intact skin or from simply smelling foods (8).

However, if you touch contaminated foods and then touch your face, the toxin can be absorbed through mucus membranes in the eyes or nose. The toxin can also infect open wounds or cracks in the skin (8).

Thus, hand hygiene, including frequent hand-washing, is important.

Inhalation botulism is rare is generally only reported in cases when the toxin is sprayed in the air or in the case of a young man who inhaled cocaine (3).

Furthermore, botulism is not considered contagious, but a person may become infected if they come into contact with bodily fluids from someone who has botulism via eyes, nose, mouth or wounded skin (8).

Botulism is a rare but severe and potentially life-threatening illness caused by neurotoxins produced by strains of the Clostridium bacteria.

Foodborne botulism is the most common cause of botulism and causes mild to severe symptoms, depending on the amount of toxin exposure.

Difficulty swallowing, headaches, abdominal pain, respiratory failure, and eventual death may occur if the illness is left untreated.

Most foodborne botulism cases are due to home-canned or bottled vegetables, meat, and fish. Few cases are linked to commercially canned olives, fish, and fruits.

Canned food safety helps to reduce the risk of botulism. Discard canned foods with signs of contamination, practice safe home-canning, cook canned foods at high temperatures, sterilize cooking equipment, and wash your hands regularly.

Just one thing

Try this today: If you practice home-canning, check out the National Center for Home Food Preservation‘s guidelines and tips to ensure safe canning practice at home that reduce the risk of contamination.