What happens in my body when I get food poisoning?

What happens in your body when you get food poisoning?

Food poisoning, also called foodborne illness, is illness caused by eating contaminated food. Infectious organisms — including bacteria, viruses and parasites — or their toxins are the most common causes of food poisoning. Infectious organisms or their toxins can contaminate food at any point of processing or production. Contamination can also occur at home if food is incorrectly handled or cooked. 

Food poisoning symptoms, which can start within hours of eating contaminated food, often include nausea, vomiting or diarrhea. Most often, food poisoning is mild and resolves without treatment. But some people need to go to the hospital. 


Food poisoning symptoms vary with the source of contamination. Most types of food poisoning cause one or more of the following signs and symptoms:

  • Nausea
  • Vomiting
  • Watery or bloody diarrhea
  • Abdominal pain and cramps
  • Fever

Signs and symptoms may start within hours after eating the contaminated food, or they may begin days or even weeks later. Sickness caused by food poisoning generally lasts from a few hours to several days.

When to see a doctor

If you experience any of the following signs or symptoms, seek medical attention.

  • Frequent episodes of vomiting and inability to keep liquids down
  • Bloody vomit or stools
  • Diarrhea for more than three days
  • Extreme pain or severe abdominal cramping
  • An oral temperature higher than 100.4 F (38 C)
  • Signs or symptoms of dehydration — excessive thirst, dry mouth, little or no urination, severe weakness, dizziness, or lightheadedness
  • Neurological symptoms such as blurry vision, muscle weakness and tingling in the arms


Food Poisoning

Most of us are all too familiar with the unpleasant symptoms of food poisoning, from vomiting to diarrhoea and debilitating stomach cramps. Although viruses play a role, bacteria are common offenders, with Salmonella and Campylobacter topping the poisoning charts. Some bacteria wreak havoc by multiplying in the body before delivering their toxins, which spark an immune reaction in the gut. Others, such as Staphylococcus aureus, poison us by contaminating food with toxins. 

Bacteria enter

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Some bacteria or enterotoxins (intestinal toxins) can survive harsh stomach conditions, making their way to the gut. There, the misery begins, sometimes up to 72 hours after eating the offending meal.

Bacteria multiply

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Undetected by the body’s immune system, the bacteria quietly multiply, producing toxins. These invade and penetrate the gut lining, setting off a strong immune response.

Immune response

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Immune cells release signalling proteins called pro-inflammatory cytokines, which set in motion a series of steps causing gut inflammation and swelling, leading to discomfort.

Flooded intestines

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The intestinal wall is designed to absorb nutrients and water from food. Bacterial toxins can cause pores to open in the wall, allowing water and other molecules to flood in.

Diarrhoea and dehydration

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The excess fluid and electrolytes in the gut lead to watery diarrhoea, which has a beneficial role of flushing out the bacteria and their toxins. It can, however, cause dehydration.


© Raja Lockey
Some bacteria don’t cause vomiting, but Staphylococcus aureus enterotoxins do. Research suggests that they may stimulate the vagus nerve which transmits a signal to the brain’s vomiting centre.