The length of time you're contagious for after having a viral infection depends on the type of virus involved.
You can often spread the infection to other people before you start to feel unwell or notice a rash.
Bronchitis
The length of time that you can spread bronchitis 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 spread the infection as long as you have cold or flu symptoms.
Chickenpox
You can spread chickenpox from 2 days before the spots appear to until they have crusted over, usually 5 days after they first appeared.
Common cold
You can spread the common cold from a few days before your symptoms appear until all of the symptoms are gone. Most people will be contagious for up to 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.
Coronavirus (COVID-19)
If you have coronavirus (COVID-19), you can spread the virus to other people for up to 10 days from when your infection starts.
But many people will no longer be contagious to others after 5 days.
Flu
You can spread flu from 1 day before your symptoms start until around 5 to 7 days after your symptoms start.
Children and people with lowered immune systems may be contagious for a few days longer.
Glandular fever
Glandular fever is usually spread through direct contact with saliva, which is why it's sometimes called "the kissing disease".
You can spread the infection from up to 7 weeks before you get symptoms until the symptoms are gone.
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.
You're most likely to spread measles from when your first symptoms appear to 4 days after the rash develops.
First symptoms of measles include:
- a high temperature
- red eyes
- cold-like symptoms – such as a runny nose, watery eyes and sneezing
Around 2 to 4 days later, a 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.
You're most likely to spread mumps from about 1 to 2 days before your glands swell until about 9 days afterwards.
Rubella (german measles)
People with rubella should stay off school or work, and avoid contact with pregnant women where possible, for at least 5 days after the rash first develops.
Shingles
You can't spread shingles to others. But people who haven't had chickenpox before could catch chickenpox from you.
You can spread the infection while the rash oozes fluid.
Tonsillitis
Tonsillitis itself isn't contagious, but the viruses that cause it are. The length of time you can spread it will depend on the virus.