What are allergic reactions?

The allergic reaction is the body’s response to a foreign substance perceived as dangerous called allergen.
Daily inspiration, ingest or touch allergenic, without realizing it, because they are usually harmless. But if the immune system identifies pollen, animal dander and other antigens harmless substances as dangerous, it can trigger an allergic reaction.The body becomes sensitized allergic-or – to a particular substance before symptoms occur. The majority of allergies are produced in this way. The first time you inhale pollen, person does not even sneeze.

When the allergen enters the nasal mucosa, certain immune cells called macrophages slowly make their appearance. Macrophages neutralize the allergen particles and then associated with certain white blood cells (lymphocytes) that defend the body of toxins. Meanwhile, other white blood cells produce a protein called immunoglobulin E (IgE), which in this case is programmed to react against pollen.
E-type antibodies sensitized to a certain allergen is then associated with mast cells in the mucous membranes of the eyes, nose and throat. Mast cells exist in the digestive tract and skin. These cells are storage rooms of chemicals that cause allergy symptoms, including histamine, responsible for producing itching and edema.

All this is happening at first contact with the allergen. After sensitization, the person will present allergy symptoms whenever exposed to the substance, which can penetrate the body via the respiratory, digestive, and skin.
The next contact with pollen allergen immunoglobulin E is fixed on the upper respiratory tract. Each particle is between two protein allergen IgE, forming antigenic bridges. Result of the formation of these bridges is activated mast cells that release histamine and other chemicals.
Many allergens that enter the body via the respiratory or digestive affect mast cells in the lower respiratory tract, causing asthma. Other allergens (nickel and latex) determine synthesis of histamine by mast cells found in the skin, resulting in rashes or dermatitis.