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Ohio State University Extension


Botulism: What You Don't See or Smell Can Still Hurt You

Family and Consumer Sciences
Barbara Rohrs
Lydia Medeiros & Jeffery LeJeune

Botulism is the name of the food poisoning we get by consuming the toxin of bacteria Clostridium botulinum. Botulism is a rare but serious foodborne disease that can be fatal. There are two different types of botulism poisoning associated with foods—adult and infant botulism.

Where Does Botulism Come From?

The bacteria, Clostridium botulinum, grow anaerobically, meaning they grow in the absence of air—in places like home-canned products and in the intestines of animals and humans. The bacteria produce spores that are very resistant to heat and chemicals, and under the right environmental conditions, can transform into an active bacteria. The spores can be found in soil all over the world and can contaminate vegetables in the field and other natural foods such as syrup and honey. The toxin that Clostridium botulinum produces is among the most deadly food toxin known. Fortunately, heat destroys the toxin and cooking is the best way to control botulism.

Symptoms of Illness

The symptoms of botulism depend upon the age of the person exposed. In adults this may include difficulty in swallowing, speech, and breathing, and double vision. The onset of botulism is usually 18 to 36 hours after eating the contaminated food, although it can be as soon as four hours and as long as eight days. In infants, signs of botulism include constipation, muscle weakness, and loss of head control, also called "the floppy baby."

Public Health Consequences

The exact number of botulism cases that occur each year is hard to determine because the local Health Department and Centers for Disease Control and Prevention (CDC) cannot record the number of cases accurately unless the ill person seeks medical care, which is unusual in mild cases. The CDC has calculated an estimate of the number of cases of botulism based on corrections for underreporting or misdiagnosis. The CDC estimates that there are 55 cases of botulism each year in this country, and that 100% of the cases are caused by eating food contaminated with the toxin produced by the bacteria. About 42 cases will be severe enough to require hospitalization; 9 deaths are possible each year.


Susceptible Groups

Anyone can become ill by eating food that has been improperly stored. Some will have more severe symptoms depending on the dose of toxin that they consume. Infants are particularly at risk.

How Can Botulism Be Prevented?

There are very few cases of botulism each year. The death rate is high if not treated immediately. Prevention is extremely important. Botulism spores can produce the toxin if mistakes are made in home canning food. Home canning should follow strict instructions and hygienic recommendations to reduce risks. Pressure canners should be used for all foods that are naturally low in acid. The botulism spores can only be killed by the high heat that can be obtained in a pressure canner. In addition, home-canned foods should be boiled for 20 minutes before tasting or eating.

Are Home-canned Foods the Only Concern?

Infant botulism is a concern for children under one year of age. It is possible for bees to pick up the botulism spores from flowers or soil. These spores are not destroyed during the processing for honey. The botulism spores grow in the baby's intestinal tract and then produce the toxin. This is less likely to occur after the age of one year when the baby's digestive tract matures.

Flavored oils also can be a concern if not prepared correctly. When herbs, garlic, or tomatoes are placed in oils, the botulism spores on the plant material can start to produce the toxin in this anaerobic mixture. To be safe, keep these flavored oils refrigerated and make only the amount of herbal oils and butters that will be used in a few days. Using dried herbs and vegetables will also reduce the risk.

Baked potatoes wrapped in foil and kept at room temperature occasionally form the anaerobic conditions the botulism spores need to produce their toxin. For this reason, leftover potatoes should be refrigerated. Potato salad made from leftover baked potatoes that have been improperly refrigerated has been implicated in botulism poisoning.

How Can I Control the Pathogen in My Home?

  1. Boil all home-canned, low-acid foods 20 minutes before eating. Low-acid foods are most vegetables, some tomatoes, and meat or poultry.
  2. Discard all raw or canned food that shows any sign of being spoiled.
  3. Discard all bulging or swollen cans of food and food from glass jars with bulging lids.
  4. DO NOT TASTE food from swollen containers or food that is foamy or has a bad odor.
  5. Process low-acid foods at temperatures above boiling (which can only occur using a pressure canner) and for the recommended time for the size of can or jar you are using.
  6. Can low-acid foods in a pressure canner. Do not can low-acid foods in the oven, in a water-bath canner, open kettle, or vegetable cooker.
  7. If you suspect that home-canned food has spoiled, heat the food to boiling to destroy possible toxin, then discard the food. Do not eat this food. Clean all surfaces with chlorine/water solution (one tablespoon of bleach per gallon of water) that leaky containers may have contaminated. Then boil any sponges or cloths used for clean-up to destroy the toxin. Then, discard the sponges or clean-up cloths.
  8. Do not give honey or foods with honey to infants under one year of age.

There are a number of organisms that can make people sick. It is not possible to determine which pathogen is causing the problem based on symptoms alone. Individuals suffering from serious illness should seek appropriate medical advice.


Centers for Disease Control and Prevention. (2022). Botulism. U.S. Department of Health & Human Services.

Scallan, E., Hoekstra, R.M., Angulo, F.J., Tauxe, R.V., Widdowson, M.A., Roy, S.L., Jones, J.L., & Griffin, P.M. (2011). Foodborne illness acquired in the United States—major pathogens. Emerging Infectious Diseases, 17(1), 7–15.

U.S. Food and Drug Administration. (1992). Clostridium botulinum. Bad Bug Book.

For more information about food safety, visit

Revised by Lydia Medeiros and Jeffery LeJeune.

Originally posted Nov 30, 2011.