A food allergy refers to an abnormal immune response to an allergen present in food. The symptoms due to this aberrant immune response are highly variable and may affect many organ systems, and in rare cases can be life threatening also.
The symptoms may be acute and easy to associate with a food allergy, for example, itching in mouth, throat and other adjacent areas, swelling of face, tongue and lips, difficulty in swallowing or breathing, nausea and vomiting, abdominal pain and skin reactions like hives, etc. Sometimes food allergies may present with atypical presentation, which may not be easy to ascribe to food allergies. An example of such a case would be neuropathy due to an allergic response to a food item. In this case, the affected person might have sensory manifestations of peripheral neuropathy like numbness, pins-and-needle sensations, burning sensations, pain or loss of sensations in one or more areas of the body. Affected person might also have motor symptoms in form of weakness of one or more muscles groups. Although peripheral neuropathy as a presenting feature of a food allergy has been documented, it is often not easy to attribute peripheral neuropathy to a food allergy. However finding the food allergy as a cause of such peripheral neuropathy is of paramount importance, and it may change your life as often the neuropathy is very frustrating not only because of the symptoms, but also because it does not respond to any other treatment. The only treatment in this case is avoidance of allergens.
Correctly identifying food allergies may change a person's life but this may not be easy in all cases. In most cases, the association might be obvious and a person may clearly recall having symptoms after eating a particular food. However, in many cases, especially when the symptoms are not acute, finding an association between a food allergy and symptoms might pose a difficult diagnostic challenge. Various allergy tests are used to test a patient for allergy. In skin prick test, the suspected allergens are introduced into the skin, and response noted. Blood tests like RAST (RadioAllergoSorbent Test), which detect specific IgE antibodies against the allergens, can also be used. Both these tests can only detect IgE allergens and not others. In another test, called Food Challenge test, the patient is given the substance suspected to be allergen and then response noted. Often it may happen that despite all this, it may not be possible to identify the allergen, especially in allergies with atypical presentation like neuropathy. In such cases, only option remaining is a hit and trial strategy, in which the common suspected allergens are removed from the diet, and response noted over a few weeks. If the person's symptoms alleviate, then the removed substance has a good chance of being the allergen.