We've encountered that with other allergens & particles. Drs explained that the in the course of reacting to the "invader" particles, the body sometimes manages to encapsulate or wall off very small amounts of the toxins/allergens. Later for whatever reason, using fat stores in that area, exertion (breaking down muscle & other fiber) normal growth & repair, the toxins or particles are re-exposed and if it is an allergen, the histamine reaction of course reoccurs.
That happens to me anything with like a flea or mosquito (I guess it is that blood thinner they use) :?. They seem to totally heal up, but then suddenly reappear almost as badly as they started :( Not a new bite, the same old one. Bee stings thankfully don't seem to do that, or I do not think I would consider working with bees :) Dr's solution is treat the "new" re-exposure with Benadryl or whatever, etc, just like the original contamination.
It can take a really long time for the particles to finally all be absorbed/dealt with. Fiberglass is one a good example.