Botulism is a rare but serious illness caused by a toxin that damages the body’s nerves and makes breathing challenging, with muscle paralysis, and even sometimes death.
The bacteria that make botulinum toxin are found naturally in many places, but it’s rare for them to make people sick. These bacteria create spores, which act like protective coatings.
Spores advances the bacteria survival in the environment, even in severe conditions. The spores commonly do not cause people to become sick, even when they’re eaten. But under certain conditions, these spores can grow and create one of the most destructive toxins ever.
The conditions in which the spores can grow and make toxin are:
- Low-oxygen or no oxygen (anaerobic) environment
- Low acid
- Low sugar
- Low salt
- A certain temperature range
- A certain amount of water
For example, ill-advised home-canned, preserved foods can build the right conditions for spores to grow and make botulinum toxin. When ingested these foods, people can become severely ill, or even die, if they don’t get medical treatment quickly.
Symptoms of botulism commonly start with weakness of the muscles that control the eyes, face, mouth, and throat.
The symptoms of botulism may include:
- double vision
- blurred vision
- drooping eyelids
- slurred speech
- difficulty swallowing
- difficulty breathing
- a thick-feeling tongue
- dry mouth
- muscle weakness
Infants with botulism symptoms may include:
- appear lethargic
- feed poorly
- be constipated
- have a weak cry
- have poor muscle tone (appear “floppy”)
These symptoms all concludes from muscle paralysis caused by the toxin. If untreated, the disease may progress and symptoms may worsen to cause paralysis of certain muscles, including those used in breathing and those in the arms, legs, and trunk (part of the body from the neck to the pelvis area, also called the torso).
Many cases of botulism are preventable.
Most cases of foodborne botulism have happened after people ate home-canned, preserved, or fermented foods that were contaminated with toxin. The foods might have become contaminated if they were not canned (processed) correctly.
Foods with low acid content are the most common sources of home-canning related botulism cases.
Examples of low-acid foods are:
- Green beans
New sources of foodborne botulism continues to be identified. Contamination can happen when food is handled improperly when it is made, when it is stored, or when it is used by consumers.
Some examples of foods that have been contaminated are:
- Chopped garlic in oil
- Canned cheese sauce
- Canned tomatoes
- Carrot juice
- Baked potatoes wrapped in foil
If you preserve, can, or ferment your own foods, you can reduce the chance of these foods giving you, your family, or friends botulism by:
- Following safe home canning instructions as recommended by the U.S. Department of Agriculture in the USDA Complete Guide to Home CanningExternal
- Following all instructions for washing, cleaning, and sterilizing items used in canning
- Using pressure canners for low-acid foods like potatoes, most other vegetables, and meats
People can decrease their chances of getting botulism by:
- Refrigerating homemade oils infused with garlic or herbs and throwing away any unused oils after 4 days.
- Keeping potatoes that have been baked while wrapped in aluminum foil hot (at temperatures above 140°F) until they are served, or refrigerating them with the foil loosened.
Home-canned vegetables are the most common cause of botulism outbreaks in the United States. From 1996 to 2014, there were 210 outbreaks of foodborne botulism reported to CDC. Of the 145 outbreaks that were caused by home-prepared foods, 43 outbreaks, or 30%, were from home-canned vegetables. These outbreaks often occur because home canners did not follow canning instructions, did not use pressure canners, ignored signs of food spoilage, or were unaware of the risk of botulism from improperly preserving vegetables.
References: Dunbar EM: Botulism [published erratum appears in J Infect 1990 May;20(3):273]. J Infect 1990 Jan; 20(1): 1-3.
 Harrison’s Principles of Internal Medicine 15th edition.
 Hatheway CL: Botulism: the present status of the disease. Curr Top Microbiol Immunol 1995; 195: 55-75[Medline].
 John Hopkins Public Health.
 Kumar P, Clark M. CLINICAL MEDICINE. WB Saunders 2002.