Causes of allergies are very important to be diagnosed before treating them. Risk factors for allergy can be placed in two general categories, namely the host and the environmental factors. Host factors for allergy include heredity, sex, race, and age, with heredity being by far the most significant. However, there have been recent increases in the incidence of allergic disorders that cannot be explained by genetic factors alone. Four major environmental candidates are alterations in revelation to infectious diseases during early childhood, environmental pollution, allergen levels, and dietary changes.

Genetic reasons prove to be some of the most vital causes of allergies. Allergic diseases are strongly familiar. The identical twins are likely to have the same allergic diseases about 70% of the time; the same allergy occurs about 40% of the time in non-identical twins. Allergic parents are more likely to have allergic children, and their allergies are likely to be more severe than those from non-allergic parents. Some allergies, however, are not reliable along genealogies; parents who are allergic to peanuts may have children who are allergic to ragweed. It seems that the likelihood of developing allergies is inborn and connected to an irregularity in the immune system.

The risk of allergic sensitization and the development of allergies vary with age, with young children most at risk. Several studies have shown that IgE levels are highest in childhood and fall rapidly between the ages of 10 and 30 years. The peak prevalence of hay fever is highest in children and young adults and the incidence of asthma is highest in children under 10; however, boys have a higher risk of developing allergy than girls, although for some diseases, namely asthma in young adults, females are more likely to be affected. Sex differences tend to be a cause of variation in the level of allergy. Ethnicity may play a role in some allergies; however racial factors have been difficult to separate from environmental influences and changes due to migration.

Hygiene Hypothesis is an important term to understand the causes of allergy. According to the hygiene hypothesis, the causes of allergy are by inappropriate immunological responses to harmless antigens driven by a TH2-mediated immune response. Many bacteria and viruses draw out a TH1-mediated immune response, which down-regulates TH2 responses. The first proposed mechanism of action of the hygiene hypothesis said that insufficient stimulation of the TH1 arm of the immune system often lead to an overactive TH2 arm, which in turn led to allergic disease. In other words, individuals living in too sterile an environment are not exposed to enough pathogens to keep the immune system busy. Since human bodies evolved to deal with a certain level of such pathogens, when it is not exposed to this level the immune system will attack harmless antigens, and thus normally compassionate microbial objects, like pollen, will trigger an immune response. The hygiene hypothesis has been extensively investigated by immunologists and epidemiologists and has become a significant theoretical framework for the study of allergic disorders.

In the contemporary health researches several experiments have been done to reveal the causes of allergy. Allergic diseases are more common in industrialised countries than in countries that are more traditional or agricultural, and there is a higher rate of allergic disease in Indian urban populations versus rural populations, although these differences are becoming less defined. Longitudinal studies in the third world state an increase in immunological disorders, as a country grows more affluent and, presumably even cleaner. The use of antibacterial cleaning products has also been associated with higher degree of asthma in India.

Exposure to allergens, especially in early life, is an important risk factor for allergy and is recognised as an important cause of allergies in India. Endotoxin exposure reduces release of inflammatory cytokines such as TNF-?, IFN?, interleukin-10, and interleukin-12 from white blood cells (leukocytes) that circulate in the blood. Certain microbe-sensing proteins, known as Toll-like receptors, found on the surface of cells in the body are also thought to be involved in these processes.

There are many causes behind developing allergies, however the cause decides the symptoms and thus the identification of particular kind of allergy leads to the proper treatment. Causes of allergies should not be neglected while diagnosed, since these are the parameters, which decide the method of treatment.