Diarrhea and Vomiting: Causes and What to Do

Diarrhea and vomiting at the same time most often mean viral gastroenteritis — a stomach bug — with food poisoning the second most likely explanation. Both are usually short and self-limited. The thing that actually determines how the illness goes is whether you keep up with the fluid you’re losing, not which of the two it turns out to be.

The likely causes, most common first

• A stomach virus. Norovirus, rotavirus, adenovirus and astrovirus. The NIDDK’s symptom set is watery diarrhea, abdominal pain or cramping, nausea or vomiting, and sometimes fever. Full picture in stomach bug symptoms.
• Foodborne illness. Bacteria or a preformed toxin in food that sat too long, was undercooked, or was handled without washing. Usually faster in onset and shorter.
• Medication. Antibiotics are the classic culprit; so are some diabetes drugs, magnesium supplements and chemotherapy.
• Food intolerance, lactose most often, sometimes appearing for the first time after a previous gut infection.
• Something that isn’t the gut at all. In young children, an ear or urinary infection can present with vomiting. In adults, severe localized pain with vomiting can mean appendicitis or gallbladder disease and needs evaluation, not fluids.

Timing separates food poisoning from a virus

Neither can be confirmed at home, but the clock is a real clue.

	Food poisoning	Stomach virus
Starts after exposure	Often 1 to 6 hours	12 to 48 hours for norovirus
Who else is sick	Everyone who ate the same thing	Household or class, over several days
Vomiting	Often abrupt and dominant	Common, usually easing first
Typical length	Under a day for toxin-mediated cases	1 to 8 days depending on the virus

If cases appear in a household one after another over a week, that staggered pattern is viral — food poisoning doesn’t spread person to person. See how long does a stomach bug last.

Rehydration, done the way the NIDDK describes it

Adults can use water, juice, sports drinks and broths, along with salty foods such as saltine crackers to help replace electrolytes. Children are a different case: they should get an oral rehydration solution — Pedialyte, Naturalyte, Infalyte or CeraLyte — as directed, because the salt-to-sugar ratio is what makes fluid absorb rather than pass through. Infants should keep drinking breast milk or formula as usual, and a doctor should be asked before giving them a rehydration solution.

Homemade salt-and-sugar solutions are used in many countries and work when measured correctly, but a mismeasured one is harmful to a small child. Where commercial oral rehydration solutions are on every drugstore shelf, there is no reason to improvise.

On food: the NIDDK says most experts do not recommend fasting or a restricted diet, and that research shows a restricted diet does not help. Eat normally when appetite returns.

The dehydration signs that decide the visit

In adults, MedlinePlus lists intense thirst, dry mouth, urinating and sweating less than usual, dark urine, dry skin, fatigue and dizziness. In infants and young children: no wet diapers for 3 hours or more, crying without tears, dry mouth and tongue, sunken eyes, and unusual sleepiness or irritability. Confusion, fainting, no urination, a racing heart or rapid breathing are emergencies at any age. The infant version is detailed in stomach bug in babies.

Get medical care if

• Diarrhea lasts more than several days, or vomiting stops nothing from coming back up
• There’s blood in the stool or the vomit, or the vomit looks like coffee grounds
• No urine for 8 hours or more
• A fever that won’t come down with medication, or one that returns after breaking
• Severe, constant, one-sided abdominal pain
• Confusion or dizziness on standing

See also viral infection symptoms for how this fits alongside the respiratory kind. This content is informational and does not replace medical evaluation, diagnosis, or treatment.