Pigs Make Me Sneeze! (Elephant and Piggie Series) by Mo Willems

Gerald and Piggie are best friends. Gerald is careful. Piggie is not. Piggie cannot help smiling. Gerald can. Gerald worries so that Piggie does not have to. In Pigs Make Me Sneeze!, Gerald believes he is allergic to his best friend! Will he have to stay away from Piggie forever?