If the immunity of our body gets disturbed, we tend to get allergies of various kinds, which are commonly known as atopy in medical terms. Environmental substances that might cause allergies are known as allergens. There are no specific substances that qualify to be allergens- any substance that causes a negative reaction in the body can be treated as one. Some of the most common allergens are pollen grains, dust, particles suspended in polluted air, or venom or sting of insects like bees and wasps.

Medically, allergies are really a type of hypersensitivity, typically known as type 1 hypersensitivity. They generally cause rapid reactions and are quite predictable. Allergies start causing a problem when the antibody, IgE in the blood activates the basophils and mast cells. This correspondingly causes an inflammation on skin or acute sneezing, reddening of eyes and so on. Acute forms of allergies include asthma, hay fever, hives, eczema and food allergies. Allergies are generally mild and do not get grave forms if taken proper precautions. However, allergies should never be neglected because they can give you serious troubles if you cannot identify the allergens or take proper precautions to protect yourself these substances. As an example, if you take pollution to be an allergen, there is hardly any way you can avoid it if you reside or are forced to work in a highly polluted area. Such cases require acute medical attention. In fact allergies like asthma can put your life at a risk!

Allergies affect various parts of the human body. Allergies affecting the nose mucosa and causing it to swell up is known as allergic rhinitis. Often due to lack of Eustachian Tube drainage from the ear, there is a feeling of pain and fullness leading to impaired hearing- this is a common allergy for the ear. Hives and eczema are common allergies and rashes that erupt on skin. Redness of the conjunctiva and itching of the eyes is a form of allergic conjunctivitis, which occurs due to high levels of stress to the eyes, exposure to sunrays or even pollution and smoke. Coughing, sneezing, running nose, dyspnea and even out right bouts of asthma are forms of allergies in the air passage. Vomiting, diarrhea and abdominal bleeding are all symptoms of allergic reactions in the abdominal tract.

Allergies can be classified in to broadly two categories- those that occur because of host factors and those that manifest because of environmental factors. Host factors play quite a major role in determining what type of allergy a person might fall prey to. Among host factors like sex, heredity and age, heredity outnumbers the others. As an example, we may consider asthma which mostly runs in through generations. Environment factors are those occur due to excess of exposure to allergic diseases during early childhood or to pollen grains, pollution or dietary substances. Researches have found that people are more prone to allergies because of environmental factors, more in industrial areas than in those where agriculture is the mode of subsistence.