Indoor contact allows germs to spread more easily.
College students seem to catch more colds and flues due to this very reason. Closely living with many other students and the dry air in dorms can make even the healthiest student susceptible to infections. College students also tend to share food and drinks, as well as use a common phone or computer, which are all ways of transmitting germs. Staying up late studying for exams and getting little sleep don't help either. The eyes and nose are moist and at the right temperature to provide the perfect breeding environment for germs.