Why do gnats hover around people?

I did a Google search for information about gnats and found out that it is a generic term covering several types of insect. What I consider a gnat is an insect that tends to form swarms in warm and wet areas. They do not bite or even land on people. I have considered the possibility that they are not really attracted to people and it is just that they do not do anything to avoid bumping into them. It seems though that a particular cluster will follow you around. Is this right and, if so, what is the point of it?