People who bit their nails or sucked their thumbs when they were little are 33 percent less likely to have an allergic reaction to common allergens. According to scientists, these behaviors help build their immunity to various bacteria. 1).
There is an allergy to exercise. It is extremely rare and since the 70s has been reported only around 1000 times. Its mild form causes urticaria or hives, but in severe cases can lead to anaphylaxis. 2).
Aquagenic urticaria is an allergy to water. It is a very rare condition in which hives show up on the skin after contact with water. 3).