6 Signs of Food Poisoning, Onset and Duration

Food poisoning is an illness that we all experience several times in life, and sometimes a few times within a year. It causes about 8 million illnesses a year in the United States. For most of us, food poisoning is as an acute illness that is not serious and lasts for just a few days. It may not even require medical treatment. However, food poisoning may be responsible for about 9,000 American deaths annually.

Contaminated food and water can introduce various infectious agents into the digestive system. Viruses, bacteria and protozoa are the infectious agents that can cause disease once in the digestve tract. Sometimes these agents are not present but the toxins its produced has contaminated the food and water. These toxins can also cause an illness and may even be deadly.

Food Poisoning vs Chemical Poisoning

The term food poisoning is usually reserved for foodborne illnesses caused by infectious agents (viruses, bacteria, protozoa) and/or their toxins. In strict terms it should include all foodborne illnesses including illnesses caused by food contaminated with toxins or poisons that were not produced by viruses, bacteria or protozoa. However, the latter is often referred to as chemical poisoning or simply poisoning if from non-food or artificial sources.

Food poisoning also includes the toxins that are naturally present in some foods and produced by living organisms that are consumed as food. For example, the meat of certain poisonous fish can cause food poisoning. However, this is uncommon and only applies to certain foods.  Food poisoning gives rise to illnesses such as gastroenteritis, enterocolitis or infectious colitis. Commonly this is referred to as the stomach flu or a tummy bug.

Read more on food poisoning.

How long does food poisoning last?

Firstly it is important to understand that there is a period between the consumption of the contaminated food or water and the onset of symptoms. This is referred to as the incubation period and strictly applies to infections, whether by bacteria, protozoa or viruses. However, there can also be a delay from the time the toxins in contaminated food and water enter the body to the time the first symptoms appear.

Onset of Symptoms

The symptoms can arise anywhere between 30 minutes to several weeks after consuming the contaminated food and water. Most of the time it takes between 8 to 48 hours after exposure with most common food poisoning agents causing symptoms about 24 hours after consumption. It depends on the amount of infectious agent or its toxins within the contaminated food and water. A large dose of toxins in particular can cause symptoms almost immediately after consumption.

Duration of Symptoms

As with the delay in the onset of symptoms, the duration of symptoms can vary greatly. Most common food poisoning illnesses lasts for 48 to 72 hours. However, it can be as short as 24 hours or as long as several weeks. The latter is rare. The duration of symptoms also depends on the severity of the illness or the type of agent/toxin that was consumed. Medical treatment, where necessary, can also reduce the duration of symptoms.

What does food poisoning look like?

Not all of the signs and symptoms may be present in every case of food poisoning. It depends on the species of  virus, bacteria or protozoa that cause the illness and its virulence. It also depends on the toxicity of the toxin from these infectious agents. Furthermore, a person’s health status may also play a role. People with weakened immune systems, debilitated or with other diseases may have more symptoms and severe symptoms compared to most people.


Nausea is the most common symptom and is sometimes the only symptom. It usually arises early in the illness and often precedes other symptoms like abdominal cramps or diarrhea. It may also be one of the last symptoms to resolve. The feeling of vomiting may not always lead to vomiting, depending on the type and severity of the illness. Most of the time eating food worsens the nausea although in some cases small meals may help relieve it.


Although vomiting is usually associated with nausea, this may not always occur in food poisoning. Sometimes vomiting does not arise at all in food poisoning or may occur once or twice and subside while other symptoms persist. The severity of the vomiting can vary and there may be episodes of vomiting where all food, beverages and even gastric juices as well as bile are emptied out of the stomach.


Diarrhea is another common symptom like nausea. The stool is loose, usually watery and sometimes even bloody. A person may experience explosive diarrhea with the bowel movement being forceful. There is usually also a constant urging to pass stool, even after having a bowel movement. Copious amounts of water may be lost and it may be worsened by certain beverages and with eating food.

Abdominal Cramps

Abdominal cramps and pain may also be present. It can vary in intensity and location depending on the underlying cause and severity of the illness. Sometimes the abdominal cramps may be relieved by vomiting or after passing stool. Food usually worsens the cramping and often there is loss of appetite due to the pain and cramps. In milder cases there may be no abdominal cramps and pain with only symptoms like nausea and diarrhea being present.


A fever may not always be present in food poisoning, even when the illness is caused by an infection. The fever may be low grade, mild to moderate or even high. The severity of the fever does not always represent the severity of the infection or the seriousness of the illness. Some very severe forms of food poisoning may not even present with a fever. Furthermore, a fever can sometimes persist and recur even after the digestive symptoms resolve.


Tiredness, fatigue and weakness are other common symptoms in most cases of food poisoning. Sometimes it may be due to the foodborne illness itself while in other instances it can be due to dehydration, the main complication of food poisoning. Weakness may also accompany a fever when present. These are instances where the fatigue and weakness can persist for long periods after other symptoms resolve. Usually this is due to dehydration and deficiencies.

Other Symptoms

A host of other symptoms may also arise with food poisoning that does not involve the digestive system. For example, there may be joint pain, muscle paralysis, difficulty breathing, bleeding, heart problems and changes in heart rate and blood pressure. The signs and symptoms of dehydration may also be present depending on the severity of water and electroyte loss and the effectiveness of rehydration.

Read more on complications of food poisoning.

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