bz, many folks think they are immune if they only have infrequent exposures. Repeated exposures causes a person to become 'hyper' sensitive. An exposure followed by a repeat exposure 2 weeks later is supposed to be optimal in causing your reaction. Of course, a 3rd exposure 2 weeks afterwards, would almost kill a guy. Some folks contact it less than once a year, have a tinie red spot that goes away after a shower, and they think they aren't allergic. Learned that in a 1980 first aid class, then later I experienced it out in the real world.
