That sudden wave of nausea after a meal can leave you wondering: Was it the chicken? The salad? Something you ate yesterday?
Food poisoning is an unpleasant experience, and figuring out what caused it isn’t always straightforward. Symptoms can appear within hours of eating contaminated food, but some infections take days to develop.
The most common causes of food poisoning are harmful bacteria, viruses, parasites, and toxins that contaminate food or drinks. Raw or undercooked meat, eggs, unwashed produce, unpasteurized dairy, and improperly stored foods are frequent sources.
According to the CDC, foodborne illness affects millions of Americans each year. Most people recover, but certain infections can cause serious complications.
What actually causes food poisoning?
Food poisoning, also called foodborne illness, happens when you consume food or beverages contaminated with disease-causing organisms or harmful toxins.
There are four main categories of causes.
- Bacteria: Organisms such as Salmonella, Campylobacter and certain strains of E. coli can cause digestive infections.
- Viruses: Norovirus is a major cause of foodborne illness and spreads easily through contaminated food, surfaces and infected people.
- Parasites: Organisms such as Giardia and Cyclospora can contaminate food or water and cause intestinal illness.
- Toxins: Some bacteria produce toxins that cause illness. Certain naturally occurring toxins in foods can also make people sick.
Contamination can happen during farming, processing, transportation, food preparation, or storage.
And here’s the tricky part: Food doesn’t have to look or smell spoiled to contain harmful germs.
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Which foods are most likely to cause food poisoning?
Certain foods are more likely to carry harmful organisms, especially when they’re handled or prepared incorrectly.
Raw or undercooked meat, poultry and eggs
Raw chicken, ground beef, and eggs can contain bacteria such as Salmonella, Campylobacter, and E. coli.
Eating these foods before they’re thoroughly cooked increases the risk of infection.
Cross-contamination is another concern. If you cut raw chicken on a cutting board and then use the same board for vegetables without washing it, bacteria can transfer to food that won’t be cooked.
Use separate preparation surfaces and a food thermometer to reduce your risk.
Unwashed fruits and vegetables
Fresh produce can become contaminated through soil, irrigation water, handling, or contact with animals.
Leafy greens, sprouts, and cut melons have all been associated with foodborne illness outbreaks.
Rinse fruits and vegetables under running water before eating or preparing them. Washing reduces contamination but doesn’t eliminate every harmful germ.
Raw sprouts are particularly risky because the warm, humid conditions needed for sprouting also encourage bacterial growth.
Raw flour and uncooked dough
It’s tempting to taste cookie dough before baking, but raw flour can contain harmful bacteria.
Unlike ready-to-eat foods, flour generally hasn’t undergone a process that kills disease-causing germs.
That means both raw flour and uncooked eggs can make homemade cookie dough or cake batter unsafe to eat.
For more information about food safety alerts, read our guide on what to know about eating recalled food.
Unpasteurized dairy products
Raw milk and dairy products made with unpasteurized milk can contain bacteria such as Listeria, Salmonella, and Campylobacter.
Pasteurization uses heat to reduce harmful microorganisms without significantly changing the nutritional value of milk.
Pregnant people, young children, older adults, and people with weakened immune systems should be especially cautious about unpasteurized dairy.
Food stored at unsafe temperatures
Even properly cooked food can become unsafe when stored incorrectly.
Bacteria multiply rapidly when perishable foods sit between 40°F and 140°F, commonly called the temperature danger zone.
Refrigerate perishable foods within two hours, or within one hour when temperatures exceed 90°F.
And don’t rely exclusively on expiration dates. Many dates indicate food quality rather than safety, while dangerous bacteria may be present without obvious signs of spoilage.
Which germs commonly cause food poisoning?
Different organisms cause different symptoms, and knowing the possible source can help healthcare providers determine whether testing is necessary.
| Germ | Common sources | Typical symptoms |
| Salmonella | Undercooked poultry, eggs, produce | Diarrhea, fever, stomach cramps |
| Campylobacter | Raw poultry, unpasteurized milk | Diarrhea, abdominal pain, fever |
| E. coli (certain strains) | Undercooked ground beef, contaminated produce | Severe cramps, sometimes bloody diarrhea |
| Listeria | Certain ready-to-eat foods, unpasteurized dairy | Fever, muscle aches, sometimes digestive symptoms |
| Norovirus | Contaminated food, infected food handlers | Vomiting, diarrhea, nausea |
| Shigella | Contaminated food or water, person-to-person spread | Diarrhea, fever, stomach cramps |
Other causes include Cryptosporidium, Cyclospora, and toxin-producing bacteria.
Some infections, including botulism, are rare but potentially life-threatening. Botulism may occur after eating improperly preserved or home-canned foods and requires emergency treatment.
How quickly do food poisoning symptoms appear?
It depends on the organism involved.
Some foodborne illnesses cause symptoms within 30 minutes to several hours. Others may take days or even weeks to become noticeable.
Common symptoms include:
- Nausea
- Vomiting
- Diarrhea
- Abdominal cramps
- Fever
- Fatigue
Because symptoms can be delayed, the food responsible isn’t necessarily the last thing you ate.
The CDC’s food poisoning symptom guide explains how symptom timing varies by germ.
How can you prevent food poisoning at home?
The most effective approach is following four basic food safety principles.
The federal government’s FoodSafety.gov recommends:
- Clean: Wash your hands, utensils, and kitchen surfaces frequently.
- Separate: Keep raw meat, poultry, and seafood away from ready-to-eat foods.
- Cook: Use a food thermometer to make sure foods reach safe internal temperatures.
- Chill: Refrigerate perishable foods promptly and keep your refrigerator at 40°F or below.
These habits are particularly important when preparing meals for children, pregnant people, older adults, or anyone with a weakened immune system.
When should you see a doctor for food poisoning?
Most mild cases improve with rest and adequate hydration. However, some infections require medical treatment.
Contact a healthcare provider if you experience:
- Bloody diarrhea
- Diarrhea lasting longer than three days
- Fever above 102°F
- Frequent vomiting that prevents you from keeping liquids down
- Signs of dehydration, including dizziness, dry mouth or decreased urination
Pregnant people should contact their healthcare provider promptly if they develop fever or flu-like symptoms after possible exposure to contaminated food.
Seek emergency care for severe weakness, difficulty breathing, confusion, or other potentially life-threatening symptoms.
A healthcare provider may recommend stool testing, fluids, or other treatment depending on the suspected infection.
If you’re experiencing concerning symptoms, Zocdoc can help you find an urgent care provider or book a primary care appointment.
The bottom line
The causes of food poisoning range from contaminated produce and undercooked meat to improper storage and infected food handlers.
Although you can’t prevent every exposure, safe food preparation and storage can significantly reduce your risk.
If symptoms become severe or don’t improve, getting medical attention can help prevent complications and identify whether additional treatment is needed.
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Frequently asked questions
What is the most common cause of food poisoning?
Norovirus is a leading cause of foodborne illness in the United States. Bacteria such as Salmonella and Campylobacter are also common causes.
Can you get food poisoning from food that looks fresh?
Yes. Harmful bacteria and viruses can contaminate food without changing its appearance, smell, or taste.
How long does food poisoning last?
Many cases improve within a few days, but the duration depends on the organism and severity of the infection. Some illnesses require medical treatment.
Can food poisoning spread from person to person?
Yes. Certain infections, particularly norovirus and Shigella, can spread through close contact, contaminated hands and shared surfaces.
The information in this article is provided for general informational purposes only and should not be relied on as medical advice. It is not intended as, and Zocdoc does not provide, medical advice, diagnosis or treatment. Zocdoc does not recommend any specific provider. Find one you’ll love on Zocdoc today.