Allergy Symptoms & Causes

Allergies can affect any part of the body, including the intestinal tract, the bladder, and even the nervous system. An allergy evaluation should be considered for anyone troubled by frequent nasal, eye, ear, sinus or lung symptoms. The most common allergic conditions involve:
nose and sinuses
Allergies can contribute to:
poor concentration 
sleep disturbance
Allergies’ affects on children can be more intense, including:
moodiness fidgeting
rubbing nose and eyes
making clucking sounds in their throat to the point that they distract other kids in the classroom 
Allergies can affect a child’s study habits, academic problems, and could even lead to a misdiagnosis of attention deficit-hyperactivity syndrome.
Your immune system does not make allergic antibodies to something it has never encountered. It needs at least one exposure to a substance to trigger the production of allergic antibodies against it. Once your immune system starts producing allergic antibodies, that substance becomes one of your allergens and can trigger allergy symptoms when exposed. 
Inhaled Allergens
For inhaled allergens, it usually takes many exposures to something before your immune system produces enough antibodies against it to cause noticeable symptoms. Inhaled allergens from pollens, animals, dust mites and mold spores are responsible for most problems. 
Skin Allergies
The resin from poison oak, ivy and sumac contains substances that cause allergic skin reactions in most people. Similar skin allergies can be caused by contact with a number of other substances. These include some metals like nickel and chromium, some medications like neomycin, some preservatives found in skin care products, and a variety of other chemicals. The rash caused by contact with these substances is called allergic contact dermatitis. 
Common allergens include:
components of pollens
animal products 
dust mites
mold spores
insect venoms 
Instant Allergy?
People can develop allergies quite quickly, especially to insect stings and some types of medications and food. Confusion tends to result from unrecognized encounters. For instance, patients who experience an allergic reaction to penicillin from their first-ever injection may have unknowingly ingested the antibiotic in milk that came from cows being treated with it.