Mono cannot be "caught" twice. Mono is a viral infection that live in your body once you come in contact with it. You become a carrier, so be aware that you could possibly give mono to someone else. Some people only have mono for a short time (a month or less) while others have recurrent mono (mono effects them for several months to several years) It may seem like someone "gets" mono several time while in actuality, their body is battling the virus - sometimes the virus is stronger, sometimes the immune system is stronger. The virus "takes over" your immune system when it is in a weakened state - so things like an unhealthy diet, lack of sleep or extreme stress can make the immune system weaker, and then mono will take over again. That is why it is very important to support your immune system if you have mono so that you can stay healthy!