I find that my body tends to overreact to certain stimuli. Grass and certain plants make my skin itchy, pollen makes me sneezy and my eyes red. Certain fruits make my throat itch. Though POIS symptoms are very different from allergies and the "allergic to own semen" hypothesis has been mostly discredited, I think an overactive immune system could still be a common underlying trait in sufferers. I'm interested to see how our rate of hay fever differs, if at all, from the general population.