Do i have to be careful not to catch a cold?

Yes: Most people catch several viral infections ( the common cold) a year and symptoms of congestion and cough resolve in a few days without complications however if you are immunosuppressed due to another medical condition, it is important to try and avoid catching viral illnesses that may interfere with your treatment or make your primary illness worse. Frequent handwashing helps!

Not sure: I am not certain of the question. It is impossible to prevent a person from catching a cold. By definition, this is a viral infection caused by a number of viruses, most commonly rhino-virus. I am not suggesting that a cold could not be complicated by more serious sequelae, but aside from sinusitis, colds are usually self limited. Nevertheless, a cold may occur no matter what you do.