The Known Causes Of Allergies
Generally speaking, allergy is an over-response by the individual's immune system to substances that are not directly harmful. However, the allergic reaction (response) can be harmful, often resulting in tissue swelling and inflammation, sometime with secondary complications. One thing leads to another. Allergy treatments include avoidance, medication and allergy shots or drops (immunotherapy).
Allergy symptoms and causes vary widely, from none to incapacitating or even life threatening (peanut), yet there is no single cause or universally allergic response. Some allergens are common and well known (ragweed, grass, pollen, pet dander, and dust mites) while others can be important but not commonly recognized (iodine in table salt), making diagnosis difficult. Some "allergies" are actually a toxicity ('black mold') with symptoms mimicking those of other allergens.
A common misperception is that contact with a possible allergen (cat dander for example) over many years makes it less likely to cause symptoms. On the contrary, repetitive exposure over time is what causes the immune system to (mis)identify an allergen as "bad" causing an inappropriately strong immune response.
Patient awareness of their home, work and dietary details (dusty, damp, malodorus indoors; foods that make one feel poorly) combined with appropriate allergy testing, will give answers in most cases. That said, allergies can result from virtually any exposure, with infinite possible causes.
