The challenge with masks is while they do trap viruses and particulates the viruses are still there on the mask. If you touch it, and then touch around your eyes, bingo. Or if you remove it and touch your face, bingo.
If you use a mask, never touch it (not easily done) except to put on / take off. And once you've removed it wash your hands thoroughly. (Thoroughly meaning lots of soap and water - and sing "Happy Birthday" to yourself. That duration is about right.)
Many people you see wearing masks are not doing it to keep viruses out, they are doing it because they have a cold or a cough and they are polite enough to try and not spread it. A sincere attempt, but I'm not certain it is terribly effective.
Oh yah, whatever you do wash your hands frequently when travelling. Soap and water if you can, sanitizer if you can't. The environment you will be in, from bag-drop to bag pick-up, is fraught with opportunities to pick up someone else's bugs. The airplane is about the safest place, but even then ...