It's a rare allergy, but if your skin is hypersensitive already, it would make a sperm allergy seem more significant than for most people.
While the medical community once thought this wasn't possible, they have recently reconsidered. However, it's not the sperm you'd most likely allergic to, but rather the proteins in the semen. That's one way to be allergic.
In some men and women, an allergy to semen could be a sign of something much more worrisome. "The immune system of some men and women see sperm as a foreign invader, like a germ, and their bodies make antibodies to attack the sperm." Antisperm antibodies may cause infertility by preventing the sperm from reaching and fertilizing the egg.
Almost all men who have undergone a vasectomy (surgical operation that causes sterility) produce antisperm antibodies after the procedure. If a man undergoes a vasectomy reversal, the antisperm antibodies will interfere with conception.
So what causes the immune system to make antisperm antibodies? A genital tract infection, a congenital abnormality in the male genital tract, a vasectomy (as mentioned above) or a varicocoele (a varicose vein in the testicles) can cause these antibodies to develop. Wives of men with abnormal sperm are also at increased risk for developing antisperm antibodies.