It sounds like either a real allergy or a psychosomatic allergy.

I dont want to be a bring down but if he has develpoed and intolerance to something he used to handle maybe the gear has changed if not then if it is a violent reaction to someting he previously tolerated. If its a problem tell him to see a doctor, perhaps something has changed in his body. But if its not a problem for him he should forget it and save the money for a new car or holiday