How long is someone infectious after a viral infection?

The length of time you're infectious for after having a viral infection depends on the type of virus involved.

The infectious period often begins before you start to feel unwell or notice a rash.

Bronchitis

The length of time that bronchitis is infectious varies, depending on its cause.

In most cases, bronchitis is caused by the same viruses that cause the common cold or flu, and you're likely to be infectious as long as you have cold or flu symptoms.

Chickenpox

Chickenpox is infectious from 2 days before the spots appear to until they have crusted over, usually 5 days after they first appeared.

Common cold

The common cold is infectious from a few days before your symptoms appear until all of the symptoms are gone. Most people will be infectious for around 2 weeks.

Symptoms are usually worse during the first 2 to 3 days, and this is when you're most likely to spread the virus.

Flu

Flu is usually most infectious from the day your symptoms start and for a further 3 to 7 days.

Children and people with lowered immune systems may be infectious for a few days longer.

Glandular fever

Glandular fever isn't particularly contagious and can usually only be spread through direct contact with saliva, which is why it's sometimes called "the kissing disease".

There's no reason not to continue to go to school or work if you feel well enough.

Measles

Symptoms of measles appear around 10 days after you become infected.

Measles is most infectious after the first symptoms appear and before the rash develops.

First symptoms of measles include:

  • a high temperature
  • red eyes
  • cold-like symptoms – such as a runny nose, watery eyes, swollen eyelids and sneezing

Around 2 to 4 days later, a red-brown spotty rash develops that normally fades after about a week.

Mumps

Mumps causes your salivary glands to swell. These glands are just below and in front of your ears.

Mumps is most infectious from a few days before your glands swell until a few days afterwards.

Rubella (german measles)

People with rubella should stay off school or work, and avoid contact with pregnant women where possible, for 6 days after the rash firsts develops.

Shingles

You can't spread shingles to others. But people who haven't had chickenpox before could catch chickenpox from you.

Shingles is infectious while the rash oozes fluid.

Tonsillitis

Tonsillitis itself isn't contagious, but the viruses that cause it are. The length of time you're infectious will depend on the virus.

Find out more about what causes tonsillitis

Further information

Page last reviewed: 13/11/2018
Next review due: 13/11/2021