Causes

The most common cause of mononucleosis is the Epstein-Barr virus, but other viruses also can cause similar symptoms. This virus is spread through saliva, and you may catch it from kissing or from sharing food or drinks.

Although the symptoms of mononucleosis are uncomfortable, the infection resolves on its own without long-term effects. Most adults have been exposed to the Epstein-Barr virus and have built up antibodies. This means they're immune and won't get mononucleosis.