We often refer to allergies, yet what exactly are they and how do they occur? An allergic reaction, also known as a metamorphosis, is an abnormal reaction of the body to one or more substances that are harmless to most people. Its main cause is due to the production of excess immunoglobulin E (IgE) antibodies in the body of the allergic person. It reacts with allergens in the environment and stimulates the body to produce and release certain chemicals in excess, which in turn produces various allergic symptoms. There are many types of allergies, the common ones are pollen allergy, food allergy, respiratory allergy (e.g. allergic rhinitis) Proper understanding of allergic diseases Allergic rhinitis AR is a seasonal, chronic disease caused by constriction of the bronchial tubes, which causes inflammation of the nasal passages. Patients often mistake themselves for a cold. Symptoms: runny nose, sneezing, nasal congestion, itchy nose, frequent midnight attacks leading to lack of sleep, etc. Note: Patients with allergic rhinitis can develop chronic sinusitis as the number of eosinophilic white blood cells (ECP) in the body increases and the symptoms become more severe. Rhinitis and asthma often occur in the same person at the same time, and about 30% to 40% of patients with rhinitis who did not improve their allergies during infancy are likely to have complications. Allergic asthma has many causes, most of which are due to excessive reactions of the trachea and bronchi to allergens or irritants in the environment (mostly inflammation and constriction of the trachea and bronchi) Symptoms: persistent cough, breathlessness, chest tightness, shortness of breath…etc. Often attacks and intensifies at night and/or early in the morning, most patients can relieve themselves or with treatment. Note: Rhinitis and asthma often occur in the same person, and about 60% to 80% of asthma patients may have a concurrent crisis of rhinitis. Asthma symptoms are also often triggered by nasal discharge, nasal congestion, and nasal mucus backflow. Atopic dermatitis AD is a chronic, pruritic, relapsing, inflammatory skin disease. The basic symptom is itchiness, and it is characterized by a genetic constitution. Note: Infancy (between 2 months and 2 years of age): Most of the rash is flushed and eczema-like on the forehead, cheeks, or neck, sometimes with small blisters or maceration from scratching too much. Early Childhood: The rash is widespread and spreads over the body, mainly on the flexors of the limbs, the bends of the arms, and the folds of the skin in the knee pits, but due to prolonged scratching, tinea cruris may gradually appear. Adult phase: From puberty to the early twenties, the rash is mainly dry and sensitive. Allergic conjunctivitis Allergic inflammation of the conjunctiva often occurs in people with allergies, especially in children with a history of allergic rhinitis, asthma and atopic inflammation. Symptoms: itchy eyes, watery eyes, burning sensation, red eyes and watery discharge, conjunctiva may appear pink due to congestion or milk-colored due to edema, etc. Note: In addition to eye discomfort, patients may also have nasal allergy symptoms. The main allergens of allergy may be dust mites, animal fur, suspended dust in the air, cold and humid air, specific odors…. etc. Urticaria, also known as urticaria and puffy rash, is a recurrent papular, rash attack that produces an inflammatory reaction (redness, swelling, heat, pain) in severe cases. 80 of patients are caused by allergens. Chronic urticaria: episodes lasting more than six weeks. Acute urticaria: Episodes of less than six weeks. Symptoms: The rash is very similar to a mosquito bite, with a red bulge or even a large patch, often uncontrollable and growing all over the body, often fading on its own, and often recurring. Note: Most acute hives are due to foods such as nuts, shelled seafood or tomatoes, or medications.