How Long Am I Contagious? A Guide by Illness

How long you are contagious depends on the illness. A cold or flu spreads most in the first two or three days. A stomach bug spreads most while you are being sick and for a few days after. Chickenpox spreads until every spot has crusted over. Some infections stop spreading a day after starting treatment. The table below gives each one.

Dr. Pedro Yelamo Vera is a GP licensed in Spain (Colegiado No. 484814280).

For a medical emergency, call 112 or go to the nearest local emergency department. Do not wait for a video consultation or an online reply.

How long am I contagious? The table by illness

These are usual ranges, not promises. People with a weak immune system can stay contagious for longer.

Illness	When it spreads most	Back to school or work
Common cold	First 2 to 3 days. Usually not after the first week.	When there is no fever and you feel well enough.
Flu	From about 1 day before symptoms to 5 to 7 days after.	When the fever has gone and you feel well.
COVID-19	Mostly the first days. Children for less time than adults.	UK: 3 days after a positive test for under-18s, 5 days for adults.
Stomach bug (norovirus)	While you are being sick and a few days after. It can spread for 2 weeks or more.	48 hours after the last vomiting or diarrhoea (UK).
Chickenpox	2 days before the spots until all have crusted.	When every spot has crusted, usually about 5 days.
Hand, foot and mouth disease	Mostly the first 5 days.	As soon as your child feels well, even with blisters.
Impetigo	Until the sores crust, or 48 hours after treatment starts.	48 hours after treatment starts, or once all sores have crusted.
Conjunctivitis	While the eye is red and sticky.	UK: no need to stay off. Many Spanish nurseries: 24 hours after antibiotic drops start.
Strep throat and scarlet fever	Until 12 to 24 hours after antibiotics start.	24 hours after starting antibiotics (UK and Spain). The CDC says at least 12 hours, with no fever.
Scabies	Until treated. The rash can take up to 8 weeks to show.	Under 5s: 24 hours after the first treatment. Older children and adults: once treatment has started.
Threadworms	Eggs can live up to 2 weeks outside the body.	No time off needed. Treat the whole household.
Head lice	Until treated.	No time off needed.

Sources for the table: the UKHSA exclusion table, NHS pages, the CDC and the Spanish primary care paediatricians' guide (Familia y Salud, AEPap).

How long is a cold, flu or COVID contagious?

A cold spreads most in the first two or three days. MedlinePlus says it is usually not contagious after the first week. More in how long a cold lasts.

Flu spreads from about a day before you feel ill until five to seven days after, according to the CDC. You are most contagious in the first three days. See flu symptoms and how long flu lasts.

For COVID, the NHS says children tend to be infectious for less time than adults. After a positive test, it advises staying home for 3 days if you are under 18, or 5 days if you are an adult. Avoid people at higher risk for 10 days.

When can I go back to work after flu or COVID?

The rules differ by country:

• US (CDC): go back when your symptoms have been getting better for 24 hours and you have had no fever for 24 hours without fever medicine. Then take extra care for the next 5 days, such as a mask and clean air.
• UK (UKHSA): stay home until you are well and no longer have a temperature.
• Spain: most people have not had to isolate since 2022, and since July 2023 COVID is handled like other respiratory infections. The Ministry of Health advises a mask if you have symptoms, above all around people at risk.

In Spain, time off work for illness is a baja médica from your public GP. A short note for an absence is a justificante. See our guide to a sick note in Spain.

How long is a stomach bug contagious?

Norovirus is the classic winter vomiting bug. The CDC says it spreads most while you are ill and in the first few days after. Studies show it can still spread for two weeks or more after you feel better.

Keep washing your hands with soap and water. If you can, do not prepare food for other people. The NHS says to stay off school or work until you have not been sick or had diarrhoea for at least 2 days. For food poisoning and when to get help, see our guide on stomach bugs in Spain.

How long is chickenpox contagious?

The NHS says chickenpox spreads from two days before the spots appear until all of them have formed a scab. That is usually about five days after the spots appear. The spots show up one to three weeks after contact.

Keep away from newborn babies, pregnant women and people with a weak immune system. Chickenpox can be dangerous for them. If you are pregnant and have been near someone with chickenpox, speak to a doctor today.

Which illnesses do not need time off?

UK guidance says there is no need to stay off for:

• Hand, foot and mouth disease, once your child feels well. The blisters do not need to heal first.
• Threadworms. The NHS advises treating everyone in the home aged 2 and over at the same time.
• Head lice. Treat them and go back to class.
• Conjunctivitis, unless your child feels very unwell.
• A slight cold without fever.

Spanish nurseries can be stricter. The AEPap guide suggests a child with conjunctivitis stays home until 24 hours after antibiotic drops start. Ask your guardería or school for its own rules.

When are impetigo, strep throat and scabies no longer contagious?

• Impetigo: 48 hours after starting treatment, or once all the sores have crusted. See our impetigo guide.
• Strep throat and scarlet fever: UK and Spanish guidance say 24 hours after starting antibiotics. The CDC says at least 12 hours, once the fever has gone. Most sore throats are viral and need no antibiotics. See our guide to sore throat and tonsillitis.
• Scabies: the NHS says children aged 5 and over and adults can return once treatment starts. They should avoid close contact for the first 24 hours. Children under 5 return 24 hours after the first treatment. Everyone at home is treated at the same time.

How are the rules different in Spain, the UK and the US?

The UK has one national table, from the UK Health Security Agency (UKHSA). The US CDC gives general rules and leaves the details to each school. Spain has no single national list. Each region, school and nursery sets its own rules. Most follow advice like the AEPap guide.

One rule is shared by all three: a child with a fever stays home. The AEP's family site, En Familia, advises waiting until 24 hours after the fever has gone before going back to nursery.

When should you see a doctor?

See a doctor today if:

• A baby under 3 months has a temperature of 38°C or more.
• A child shows signs of dehydration, such as fewer wet nappies.
• A fever lasts 5 days or more.
• You are pregnant or have a weak immune system and have been near chickenpox.
• An eye is painful, sensitive to light, or your vision changes.

Call 112 or go to urgencias if someone struggles to breathe or cannot speak in full sentences, has sudden chest pain, collapses or has a fit, or has a rash that does not fade when you press a glass on it.

Talking it through with a doctor by video

Dr. Yelamo is a GP licensed in Spain. He sees adults, children and pregnant patients by video, every day from 07:30 to 20:30 (Spain time). In the visit he will:

• Ask when the symptoms started and who else is ill at home.
• Look at a rash, sores or a red eye on camera.
• Explain whether the illness is likely to be contagious, what helps, and the signs that mean you need to be seen in person.

He does not promise any test or prescription before the visit. Where clinically appropriate, following a genuine evaluation. Treatment and prescriptions are issued solely at the doctor's discretion based on evidence-based clinical guidelines.

A prescription is never guaranteed: it is issued only where clinically appropriate after a genuine evaluation, as a private electronic prescription under Spanish law. This service is for urgent, non-emergency care. In an emergency, call 112.

See how the Urgent Care video visit works. It lasts 15 minutes and costs €50.

This guide is general information. It does not replace a consultation with your doctor.

Frequently asked questions

Sources

• UKHSA: Public health exclusion periods in children and young people's settings
• NHS: Is my child too ill for school?
• CDC: Preventing spread of respiratory viruses when you're sick
• CDC: How norovirus spreads
• NHS: Chickenpox

Related guides

• Flu care online
• How long does a cold last?
• Flu symptoms and how long flu lasts
• Impetigo: symptoms and treatment
• Conjunctivitis and pink eye in Spain
• Flu jab in Spain