The stomach flu, known medically as viral gastroenteritis, causes diarrhea, nausea, vomiting, abdominal cramps, and sometimes fever. Symptoms typically appear one to two days after exposure and last anywhere from one to eight days depending on the virus involved. Norovirus alone causes 19 to 21 million illnesses in the United States each year, making this one of the most common infections people deal with.
Core Symptoms
The hallmark symptoms hit the digestive system hard. Watery diarrhea is usually the most persistent, often accompanied by waves of nausea and vomiting. Cramping or pain in your abdomen tends to come and go, frequently worsening just before a bout of diarrhea. Some people also develop a low-grade fever, though not everyone does.
Beyond the gut, you may feel generally wiped out. Body aches, headaches, and chills are common, especially early on when your immune system is ramping up its response. These whole-body symptoms can make the stomach flu feel similar to the regular flu at first, but the respiratory symptoms (cough, sore throat, congestion) that define influenza are absent. If your misery is centered in your stomach and intestines, it’s almost certainly gastroenteritis.
How Quickly Symptoms Appear
The timeline depends on which virus you caught. Norovirus, the most common culprit in adults, has an incubation period of one to two days. You feel fine, then symptoms hit relatively suddenly. Most people with norovirus feel better within a day or two of symptoms starting, though diarrhea can linger a bit longer.
Rotavirus, which is more common in young children, takes one to three days to incubate and tends to last longer: three to eight days. The vomiting with rotavirus often comes first and can be intense for the first couple of days before diarrhea takes over as the dominant symptom.
Stomach Flu vs. Food Poisoning
These two conditions look similar but behave differently. The stomach flu has that 24- to 48-hour incubation window, meaning you won’t feel sick right away after exposure. Food poisoning, on the other hand, comes on fast, typically within two to six hours of eating contaminated food. If you were fine at dinner and violently ill by midnight, food poisoning is the more likely explanation.
Duration differs too. Viral gastroenteritis generally lingers for about two days, sometimes longer. Food poisoning tends to be briefer and more explosive, burning through your system in a shorter window. Both can cause vomiting and diarrhea, but the rapid onset of food poisoning is the clearest distinguishing feature.
Symptoms in Babies and Young Children
Children get the same core symptoms adults do, but they’re harder to spot in babies who can’t tell you what’s wrong. Watch for frequent vomiting, watery or unusually loose stools, fussiness, and a noticeable drop in energy. Babies may refuse to feed or nurse poorly.
The biggest concern with young children is dehydration, which can develop quickly because of their small body size. A key warning sign in infants: no wet diaper for six hours or longer. A dry mouth, crying without tears, and skin that doesn’t flatten back right away after being gently pinched are also indicators that fluid loss has become significant. Bloody diarrhea or a fever of 102°F (38.9°C) or higher in a child warrants prompt medical attention.
Dehydration: The Main Complication
The stomach flu itself is rarely dangerous. Dehydration is what sends people to the hospital, accounting for a large share of the roughly 109,000 norovirus hospitalizations that happen in the U.S. each year. When you’re losing fluids from both ends and struggling to keep anything down, your body can fall behind fast.
In adults, signs of dehydration include dark-colored urine, a dry or sticky mouth, dizziness when standing, and reduced urination. You might also notice that your skin feels less elastic. If you pinch the skin on the back of your hand and it stays tented for a moment rather than snapping back, that’s a sign you need fluids. Adults 65 and older face the highest risk of serious complications, including the roughly 900 annual deaths linked to norovirus.
The goal is to sip small amounts of fluid frequently rather than gulping large amounts, which can trigger more vomiting. Clear broths, electrolyte drinks, and fruit juice popsicles help replace both water and the salts your body is losing. If you can’t keep any liquids down for 24 hours, that’s a threshold where medical help becomes important.
Red Flags That Need Medical Attention
Most stomach flu cases resolve on their own, but certain symptoms signal something more serious:
- Blood in vomit or stool. This is not a normal feature of viral gastroenteritis and could indicate a different condition or a complication.
- Vomiting or diarrhea lasting more than two days. At that point, the risk of dehydration rises significantly.
- Severe stomach pain. Mild cramping is expected, but intense, localized pain could point to another problem.
- Fever above 104°F (40°C) in adults. A low-grade fever is common with the stomach flu. A high fever suggests the infection may be more serious or bacterial rather than viral.
- Inability to keep liquids down for 24 hours. This is the point where IV fluids may be necessary.
What Recovery Looks Like
Recovery from the stomach flu is gradual rather than sudden. The vomiting typically stops first, often within a day or two. Diarrhea tends to hang on a bit longer, and your appetite may be slow to return. You’ll notice that you can tolerate small sips of fluid without nausea, then small bites of bland food, then progressively normal meals.
What you eat during recovery matters. Foods high in fat, sugar, caffeine, or dairy can retrigger vomiting or diarrhea even after you start feeling better. Stick with easy-to-digest options like saltine crackers, broths, plain rice, and toast. The salt in crackers and broth helps replace electrolytes you’ve lost. Reintroduce your normal diet slowly over a day or two once your stomach can handle bland foods without protest.
For most people, the entire experience from first symptom to feeling normal again takes three to five days. You may still feel tired and slightly off for a day or two beyond that as your body finishes recovering.