Is a condition caused by hypersensitivity of the immune system to something in the environment that usually causes little or no problem in most people. These diseases include hay fever, food allergies, atopic dermatitis, allergic asthma, and anaphylaxis.
Symptoms may include red eyes, an itchy rash, runny nose, shortness of breath, or swelling. Food intolerances and food poisoning are separate conditions.
Common allergens include pollen and certain food. Metals and other substances may also cause problems. Food, insect stings, and medications are common causes of severe reactions. Their development is due to both genetic and environmental factors.
The underlying mechanism involves immunoglobulin E antibodies (IgE), part of the body’s immune system, binding to an allergen and then to a receptor on mast cells or basophils where it triggers the release of inflammatory chemicals such as histamine.
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.
Hives also known as urticaria, is a kind of skin rash with red, raised, itchy bumps. They may also burn or sting. Often the
patches of rash move around. Typically they last a few days and do not leave any long-lasting skin changes. Fewer than 5% of cases last for more than six weeks. The condition frequently recurs. Hives frequently occur following an infection or as a result of an allergic reaction such as to medication, insect bites, or food. Psychological stress, cold temperature, or vibration may also be a trigger. In half of cases the cause remains unknown. Risk factors include having conditions such as hay fever or asthma.
Diagnosis is typically based on the appearance. Patch testing may be useful to determine the allergy.
Dermatitis, also known as eczema, is a group of diseases that results in inflammation of the skin. These diseases are characterized by itchiness, red skin, and a rash. In cases of short duration there may be small blisters while in long-termcases the skin may become thickened. The area of skin involved can vary from small to the entire body.
Dermatitis is a group of skin conditions that includes atopic dermatitis, allergic contact dermatitis, irritant contact dermatitis, and stasis dermatitis. The exact cause of dermatitis is often unclear. Cases are believed to often involve a combination of irritation, allergy, and poor venous return.
The type of dermatitis is generally determined by the person’s history and the location of the rash. For example, irritant dermatitis often occurs on the hands of people who frequently get them wet. Allergic contact dermatitis, however, can occur following brief exposures to substances a person is sensitive to.
Asthma is a common long term inflammatory disease of the airways of the lungs. It is characterized by variable and recurring symptoms, reversible airflow obstruction, and bronchospasm. Symptoms include episodes of wheezing, coughing, chest tightness, and shortness of breath. These episodes may occur a few times a day or a few times per week. Depending on the person they may become worse at night or with exercise. Asthma is thought to be caused by a combination of genetic and environmental factors. Environmental factors include exposure to air pollution and allergens.
Other potential triggers include medications such as aspirin and beta blockers. Diagnosis is usually based on the pattern of symptoms, response to therapy over time, and spirometry. Asthma is classified according to the frequency of symptoms, forced expiratory volume in one second (FEV1), and peak expiratory flow rate. It may also be classified as atopic or non-atopic where atopy refers to a predisposition toward developing a type 1 hypersensitivity reaction.
Chronic obstructive pulmonary disease (COPD) is a type of obstructive lung disease characterized by long-term poor airflow. The main symptoms include shortness of breath and cough with sputum production. COPD is a progressive disease, meaning it typically worsens over time. Eventually everyday activities, such as walking up stairs, become difficult. Chronic bronchitis and emphysema are older terms used for different types of COPD. The term “chronic bronchitis” is still used to define a productive cough that is present for at least three months each year for two years.
Tobacco smoking is the most common cause of COPD, with factors such as air pollution and genetics playing a smaller role. In the developing world, one of the common sources of air pollution is poorly vented heating and cooking fires.
Long-term exposure to these irritants causes an inflammatory response in the lungs, resulting in narrowing of the small airways and breakdown of lung tissue. The diagnosis is based on poor airflow as measured by lung function tests. In contrast to asthma, the airflow reduction does not improve much with the use of a bronchodilator.
Allergic rhinitis, also known as hay fever, is a type of inflammation in the nose which occurs when the immune system overreacts to allergens in the air. Signs and symptoms include a runny or stuffy nose, sneezing, red, itchy, and watery eyes, and swelling around the eyes. The fluid from the nose is usually clear. Symptom onset is often within minutes following exposure and they can affect sleep, the ability to work, and the ability to concentrate at school. Those whose symptoms are due to pollen typically develop symptoms during specific times of the year. Many people with allergic rhinitis also have asthma, allergic conjunctivitis, or atopic dermatitis.
Allergic rhinitis is typically triggered by environmental allergens such as pollen, pet hair, dust, or mold. Inherited genetics and environmental exposures contribute to the development of allergies. Growing up on a farm and having multiple siblings decreases the risk.
The underlying mechanism involves IgE antibodies attaching to the allergen and causing the release of inflammatory chemicals such as histamine from mast cells. Diagnosis is usually based on a medical history in combination with a skin prick test or blood tests for allergen-specific IgE antibodies. These tests, however, are sometimes falsely positive. The symptoms of allergies resemble those of the common cold; however, they often last for more than two weeks and typically do not include a fever.