Allergies, also known as allergic diseases, are a number of conditions caused by hypersensitivity of the immune system to something in the environment that usually causes little problem in most people. These diseases include hay fever, food allergies, atopic dermatitis, allergic asthma, and anaphylaxis.
Common allergens include pollen and food. Metals and other substances may also cause problems. Food, insect stings, and medications are common causes of severe reactions.
Their development of allergy is due to both genetic and environmental factors.
Diagnosis is typically based on a person's medical history. Further testing of the skin or blood may be useful in certain cases. Positive tests, however, may not mean there is a significant allergy to the substance in question.
Early exposure to potential allergens may be protective.
Allergies are common. In the developed world, about 20% of people are affected by allergic rhinitis, about 6% of people have at least one food allergy, and about 20% have atopic dermatitis at some point in time. Depending on the country about 1 and 18% of people have asthma. Anaphylaxis occurs in between 0.05–2% of people.
Rates of many allergic diseases appear to be increasing.
Sinuses -- Alergic sinusitis.
Nose -- Swelling of the nasal mucosa (allergic rhinitis) runny nose, sneezing
Eyes -- Redness and itching of the conjunctiva, watery discharge from the eye (allergic conjunctivitis)
Airways -- Sneezing, coughing, broncho-constriction, wheezing and dyspnea, sometimes outright attacks of asthma (COPD, asthma, allergic from bronchitis)
Ears -- Feeling of fullness, possibly pain, and impaired hearing due to the lack of eustachian tube drainage
Skin -- Rashes, such as eczema and hives (urticaria), angioedema