I may have had them a long time but I think you may well be right in thinking that when we become aware of them, or try to clean ourselves up, they almost get hostile (is my feeling). It seemed that as long as I didn't bother them, they could go about their business of ruining my guts.
I am still wondering if there could be 2 different types of pins. It seems that most people report that they are easy to see and fairly easy to eradicate, then there are us that have an awful time trying to even see them, let alone get rid of them. It's possible that they have mutated or crossed with something else to become a super pin!