Hypersensitivity is the excessive, undesirable reactions produced by the normal immune system. Hypersensitivity reactions mediated by T cells can be activated by modified self proteins, or by injected proteins. Allergic hypersensitivity occurs when an individual, who has produced IgE antibody in response to an antigen, or allergen, gets exposed to the same allergen. Allergic hypersensitivity is immediate type hypersensitivity as it occurs seconds to minutes after allergen exposure and it may result in disorders like asthma, anaphylaxis, atopy. Allergens are nonparasite antigens that can stimulate a type I hypersensitivity response. These allergen triggers the activation of IgE-binding mast cells in the exposed tissue, leading to a series of responses that are characteristic of allergy. The most common allergens include airborne allergens such as grass, tree or weed pollen, as well as moulds. Journal Article is sometimes called a Scientific Article, a Peer-Reviewed Article, or a Scholarly Research Article. Together, journal articles in a particular field are often referred to as The Literature. Journal articles are most often Primary Research Articles. However, they can also be Review Articles. Because articles in scientific journals are specific, meticulously cited and peer-reviewed, journal databases are the best place to look for information on previous research on your species. Without a background in the field, journal articles may be hard to understand - however, you do not need to understand an entire article to be able to get valuable information from it.