1 Peanut butter allergy is a hypersensitivity reaction which may cause symptoms like vomiting, urticaria (hives), abdominal pain, diarrhea and breathing problems.2  In worse cases it may even cause reactions like anaphylactic shock which may even turn fatal in some cases. Such salmonella infected peanut butter may cause a chronic condition called Reiter's syndrome (reactive arthritis), symptoms of which includes joint pain, eye irritation and painful urination. 2  The high calorie content of peanut butter may contribute a lot to your weight gain and make you obese.