Glandular fever is an infectious illness caused by the herpes family of viruses.
Many people have already had the disease by the time they are an adult but in many cases the symptoms are so mild you may not know you've had it. If you have had glandular fever, your body makes antibodies against it so it is very rare to get it a second time.
Glandular fever is also known as the 'kissing disease' because it is spread in saliva so it can only be caught through intimate contact such as kissing. It is most common in teenagers and young adults.
Because it is difficult to catch, pregnant women are not often affected by glandular fever. There is no evidence that it harms the unborn baby if you do have the illness while you are pregnant.
In very rare cases, glandular fever can cause jaundice, hepatitis or brain inflammation. However, most people recover within a few weeks.