The condition can worsen with age. In some cases, a lactose intolerance can develop after another intestinal infection or illness. The latter example of lactose intolerance disappears when the intestinal tract returns to a normal healthy condition. Favism is a genetic disorder which involves the lack of a blood enzyme. Onset time for favism is 5 to 24 hours.
Recovery occurs when further exposure is avoided.
Possibly the largest group of sensitivities is the idiosyncratic reactions. For the most part, this group of sensitivities is simply the association of a food or ingredient with an adverse physical reaction in certain individuals. Only some of the sensitivities have been proven through extensive research while the vast majority require further scientific exploration. The other cause and effect associations are unproven. The symptom is difficulty breathing.