I believe the theory that some people are less attractive to ticks. I've lived near Rockfish Gap since the turn-of-the-century and spend a lot of time outdoors here, and haven't found a single tick this year. However, local mosquitoes in the area think I am one of the tastiest things that they have ever slurped.
I was hiking on trails about 40 miles up into SNP, not long ago, and we went through a lot of tall grass. 5 of the 7 hikers had to pick several ticks off of them, but two of us didn't find any (I know I did a very careful search). I am not confident enough to say that I am immune to ticks, but I do think that I am unattractive to them, most of the time... and I drink a lot of water.
When I get home, the clothes go into the washing machine immediately, and I go into the shower. Lyme disease is not something that you want to experience. I've heard the stories.
Greg