Stomach Flu Symptoms: 7 Key Signs and When to Seek Help
One evening you feel fine, and by the early hours you are on the bathroom floor wondering what you ate. The cluster of problems known as stomach flu symptoms (vomiting, watery diarrhoea, cramping and a wrung-out feeling) usually passes within a few days. Occasionally it turns serious, especially for babies, older adults and anyone who cannot keep fluids down.
This guide covers the seven most recognisable signs and how they differ between adults and children. It also explains how long the illness tends to last, how to look after yourself at home, and which warning signs mean you should stop waiting it out and get advice.
What “Stomach Flu” Actually Means
“Stomach flu” is a nickname for viral gastroenteritis, an infection of the stomach and intestines. Despite the name, it has nothing to do with influenza. As the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) explains, flu viruses infect the respiratory system, while viral gastroenteritis affects the intestines. Influenza tends to announce itself with a cough, sore throat and blocked nose, and you can compare these with the typical influenza symptoms if you are unsure which illness you have.
Several viruses can cause stomach flu. Norovirus is the most common, followed by rotavirus, adenovirus and astrovirus. Bacteria, parasites and contaminated food can produce very similar symptoms, so not every bout of vomiting and diarrhoea is viral. Symptoms alone cannot always tell you which germ is responsible, and that is one reason the warning signs later in this article matter.
The 7 Key Signs of Stomach Flu
Nobody has all seven at once. Some people mostly have diarrhoea, others mostly vomiting. Here is what each sign looks like.
1. Watery diarrhoea
Loose, watery stools are the signature of viral gastroenteritis. Unlike some bacterial infections, viral diarrhoea is typically watery rather than bloody. Blood or black, tarry stools suggest something other than a routine stomach virus and need medical attention.
2. Nausea
A churning, queasy feeling often arrives first, sometimes hours before anything else happens. It can come in waves and may ease briefly after vomiting.
3. Vomiting
Vomiting can be intense but is often short-lived. The NHS says vomiting usually stops within one or two days, while diarrhoea lingers longer. Because vomiting makes it hard to replace lost fluid, it is the symptom most likely to lead to dehydration.
4. Abdominal cramps or pain
Cramping tends to come in spasms and often eases after you pass stool or vomit. That pattern helps separate an ordinary gut infection from pain that needs urgent assessment. Pain that is constant, severe, or focused on one spot deserves a call to a clinician.
5. Low-grade fever
A mild temperature is common, though not universal. The NIDDK lists fever as something that occurs “sometimes”. A high fever, or any fever in a young infant, points toward a more serious problem.
6. Headache
The Centers for Disease Control and Prevention (CDC) lists headache among the other possible symptoms of norovirus. It may partly reflect fluid loss, so persistent headache alongside poor drinking is worth noting.
7. Muscle aches and fatigue
Body aches and tiredness are also listed by the CDC as occasional symptoms. Feeling drained is understandable when your body is losing fluid and fighting an infection, and this can last a day or two after the vomiting stops.
Headache, aches and fatigue are associated symptoms rather than defining ones. The core of stomach flu is the gut: diarrhoea, nausea, vomiting and cramps.
Stomach Flu Symptoms in Adults
Most healthy adults experience stomach flu symptoms in adults as a rough but short-lived illness: cramping, loose stools, nausea, reduced appetite and general weakness. Many people have only some of these. The NHS notes that its advice is the same whether you have diarrhoea and vomiting together or separately, so you do not need to vomit to have the infection.
The main risk in adults is dehydration, particularly if vomiting prevents drinking. Adults should seek advice sooner if they are older, pregnant, have a weakened immune system, or live with a long-term condition. The NIDDK recommends that these groups see a doctor right away if they have symptoms of viral gastroenteritis.
Stomach Flu Symptoms in Children and Babies
Children usually have the same symptoms, but they cope less well with fluid loss. Babies and young children can become dehydrated within a day or two, which is why parents need to watch fluid intake and wet nappies, not just vomiting and stool frequency. The NIDDK warns that diarrhoea is especially dangerous in newborns and infants.
In a child, look for:
- fewer wet nappies, or urinating much less than usual
- a dry mouth and few or no tears when crying
- unusual sleepiness, fussiness or lack of energy
- difficulty keeping fluids down
The NHS advises calling 111 if you are worried about a baby under 12 months, if a child stops breast or bottle feeding while ill, or if a child under five shows signs of dehydration such as fewer wet nappies. Parents sometimes mistake a bad winter virus for influenza, and a guide to flu symptoms in kids can help you see how the two illnesses differ.
How Long Do Stomach Flu Symptoms Last?
There is no single answer, because it depends on the virus. For norovirus, the NIDDK and CDC both say symptoms usually begin 12 to 48 hours after exposure and most people recover in one to three days. Other viruses run longer.
| Virus | Symptoms usually begin | Usually lasts |
|---|---|---|
| Norovirus | 12–48 hours after exposure | 1–3 days |
| Rotavirus | About 2 days | 3–8 days |
| Adenovirus | 3–10 days | 1–2 weeks |
| Astrovirus | 4–5 days | 1–4 days |
Source: NIDDK, Symptoms & Causes of Viral Gastroenteritis.
The NHS gives a practical guide for adults and children: vomiting usually stops within one or two days, and diarrhoea usually stops within five to seven days. So a gut that feels unsettled for several days after the vomiting has gone is not necessarily a sign that something is wrong. Diarrhoea beyond seven days, or vomiting beyond two days, is a reason to call 111.
Recovery times are guides rather than promises. If you are getting worse instead of better, or you are not sure whether what you are seeing is normal, ask for advice.
How to Treat Stomach Flu at Home
There is no medicine that cures viral gastroenteritis. The CDC says there is no specific treatment for norovirus, and antibiotics will not help because they fight bacteria, not viruses. How to treat stomach flu at home therefore comes down to replacing fluid and letting your body recover.
Fluids first. The NHS recommends drinking lots of fluids, such as water or squash, taking small sips if you feel sick. Sip steadily rather than gulping, since large mouthfuls are more likely to come straight back up. The NHS also advises against fruit juice and fizzy drinks, which can make diarrhoea worse.
Consider oral rehydration solution. For mild dehydration, the CDC says over-the-counter oral rehydration fluids are most helpful. Sports drinks and other drinks without caffeine or alcohol can help, but they may not replace important nutrients and minerals. A pharmacist can recommend rehydration powders, which is especially worthwhile for older people and anyone at higher risk of dehydration.
Keep babies feeding. The NHS advises carrying on with breast or bottle feeding. If your baby is being sick, try smaller feeds more often than usual. Do not water formula down, because it should be made up at its usual strength.
Eat when you can. You do not have to fast or stick to a rigid bland diet. Eat when you feel able, and if fatty or spicy food upsets your stomach, leave it for now.
Use medicines carefully. The NHS says paracetamol can ease discomfort, but you should check the leaflet before giving it to a child. Do not give aspirin to children under 16, and do not give children under 12 medicine to stop diarrhoea. In adults, a pharmacist can advise whether an anti-diarrhoea medicine is appropriate.
Remedies such as ginger or probiotic supplements are popular, but they are not recommended here because the sources used for this article do not establish that they help.
Signs of Dehydration to Watch For
Dehydration is the most common complication of viral gastroenteritis, according to the NIDDK. The signs differ slightly between adults and young children.
| Sign | Adults | Babies and young children |
|---|---|---|
| Thirst and mouth | Extreme thirst, dry mouth | Thirst, dry mouth |
| Urination | Passing less urine, dark-coloured urine | Fewer wet nappies, none for 3 hours or more |
| Energy | Feeling tired | Lack of energy, unusual sleepiness or fussiness |
| Eyes and tears | Sunken eyes or cheeks | No tears when crying, sunken eyes or cheeks |
| Dizziness | Light-headedness or fainting | Not usually reported |
Sources: NIDDK and CDC.
Anyone with signs of dehydration should see a doctor promptly, according to the NIDDK, and severe dehydration may need treatment in hospital.
When to Seek Help
Most cases can be managed at home. These are the situations where they should not be.
Call NHS 111 (or contact your doctor) if:
- you are worried about a baby under 12 months, or a child stops breast or bottle feeding
- a child under five has signs of dehydration, such as fewer wet nappies
- you or your child keep being sick and cannot keep fluids down
- signs of dehydration continue after using oral rehydration sachets
- there is bloody diarrhoea or bleeding from the bottom
- diarrhoea lasts more than seven days, or vomiting more than two days
Blood in the stool can point to a bacterial infection rather than a routine stomach virus, and a guide to the symptoms of E. coli infection explains why this matters.
Call 999 or go to A&E if you or your child:
- vomit blood or have vomit that looks like ground coffee
- have green vomit (adults) or yellow-green or green vomit (children)
- have a stiff neck and pain when looking at bright lights, or a sudden, severe headache
- have a sudden, severe tummy ache
- have blue, grey, pale or blotchy skin, lips or tongue, or severe difficulty breathing
- are confused or not responding as usual
These thresholds come from NHS guidance. The NIDDK takes a more cautious line for adults, advising a doctor visit for diarrhoea lasting more than two days, frequent vomiting, six or more loose stools a day, high fever or severe pain. Different sources draw the line in different places, so if you are worried, seek advice earlier rather than later. If you are outside the UK, contact your local doctor or emergency number instead.
Preventing the Spread
Norovirus in particular spreads very easily. The CDC notes you can still pass it on for two weeks or more after feeling better, so careful habits matter even once you are well. For stomach flu prevention, the NHS and CDC recommend:
- washing your hands with soap and water frequently, especially after using the toilet and before preparing food
- washing clothing or bedding soiled with vomit or stool separately on a hot wash
- cleaning toilet seats, flush handles, taps, surfaces and door handles daily
- not preparing food for other people while you are unwell, and not sharing towels or utensils
- staying off work or school until you have not been sick or had diarrhoea for at least 48 hours
- avoiding swimming pools until at least 48 hours after symptoms stop
Rotavirus is the exception, as vaccines can prevent it, according to the NIDDK.
Frequently Asked Questions
Is stomach flu contagious?
Yes. Viral gastroenteritis spreads through contact with an infected person’s stool or vomit, contaminated surfaces, food and water. People without symptoms can also spread it. Handwashing and cleaning are the best ways to protect those around you.
How is stomach flu different from food poisoning?
The symptoms overlap, and both involve vomiting, diarrhoea and cramps. Food poisoning usually follows a specific contaminated meal, while a stomach virus often spreads from person to person in a household. If several people fell ill after the same meal, food poisoning becomes more likely. This comparison of stomach bug versus food poisoning explains further. Treatment at home is largely the same, and the warning signs above apply to both.
Can I have stomach flu without vomiting?
Yes. Some people mainly have diarrhoea and cramps, and the NIDDK describes the symptoms as nausea or vomiting rather than both together. The NHS says the same advice applies whether you have diarrhoea and vomiting together or separately.
When can I go back to work or school?
The NHS advises staying off until you have not been sick or had diarrhoea for at least two days. The CDC gives similar advice for norovirus, recommending that you stay home for 48 hours after symptoms stop.
Should I take anti-diarrhoea medicine?
Not automatically. The NHS says children under 12 should not be given medicine to stop diarrhoea. For adults, a pharmacist can say whether it is suitable, and it should be avoided if there is blood in the stool or a high fever.
The Bottom Line on Stomach Flu Symptoms
Recognising stomach flu symptoms early helps you respond calmly. Diarrhoea, nausea, vomiting and cramps, sometimes with fever, headache or aches, are typical of a gut infection that most healthy people ride out within a few days with rest and steady fluids. The skill is in telling an ordinary bout from a worrying one. Dehydration, bloody stools, severe pain, symptoms that drag on, and any illness in a young baby are the cues to ask for help rather than wait.
If you are caring for someone and unsure, call 111 or your local doctor. It is always reasonable to check.
References
- NHS. Diarrhoea and vomiting. https://www.nhs.uk/symptoms/diarrhoea-and-vomiting/
- National Institute of Diabetes and Digestive and Kidney Diseases. Symptoms & Causes of Viral Gastroenteritis (“Stomach Flu”). https://www.niddk.nih.gov/health-information/digestive-diseases/viral-gastroenteritis/symptoms-causes
- Centers for Disease Control and Prevention. About Norovirus. https://www.cdc.gov/norovirus/about/index.html
Dr. Sana Lodhi is a qualified medical doctor (MBBS) with a strong commitment to patient care and evidence‑based medicine. With years of clinical experience and her current role at Liaquat University of Medical & Health Sciences (LUMHS), she brings trusted medical insights to readers, simplifying complex health topics into clear, practical guidance. Her passion lies in promoting preventive healthcare, empowering individuals to make informed decisions, and bridging the gap between medical knowledge and everyday wellness. At HealthyPost.co.uk, Dr. Lodhi shares expert perspectives on health, lifestyle, and medical awareness to help readers live healthier, more balanced lives.