Allergies affect millions of people in the United States and include environmental allergies to pollen, animals, foods, different chemicals, and certain manmade substances. Allergic responses occur when the body reacts to normally innocuous substances in the environment as it would to toxins. The body reads the allergen as an intruder, and the immune system is activated. Responses to allergens often depend on the substance. Airborne allergens most often cause respiratory responses that can range from upper airway reactions such as sneezing and nasal congestion to lower airway reactions such as wheezing and bronchial constriction. Some allergens can cause rashes, itching, or hives, often by contact with the affected area. Food allergens can cause gastrointestinal responses such as nausea, vomiting, abdominal cramping, or diarrhea. In some instances, allergens can enter the circulatory system, either immediately by injection of medicine, for example, or more slowly through digestion or inhalation, and anaphylaxis can occur. Anaphylaxis is rare but serious and involves several body systems, leading to death in some cases.
The body’s allergic response takes place in three stages: sensitization, mast cell activation, and prolonged immune activation. In the first stage, the allergen first encounters the immune system; although no reaction is produced at this stage, the body is primed for future encounters with the allergen. Immune system cells degrade the allergen and present its fragments to T cells. Antibodies are then created for that particular substance. These antibodies are then distributed to other immune cells in the body. In the second stage, the allergen encounters the body again. The body recognizes the allergen as an intruder, and chemicals are released to combat the allergy, including substances such as histamine and leukotrienes. These chemicals cause the symptoms recognized as an allergy attack. In the third stage, prolonged immune activation, mast cells continue to release the chemical substances and attract other cells to the area. The other cells become involved in fighting the allergen, and the increased production of chemicals can cause cell damage.
Airborne, environmental allergies are the most common type of allergy. These include allergic rhinitis, commonly known as hay fever, which is a seasonal allergic reaction caused primarily by pollen from trees and flowers in the spring, grasses in the summer, and weeds in autumn. Symptoms include sneezing, congestion, and watery or itchy eyes. Allergic rhinitis is diagnosed primarily by history of seasonal reactions. Perennial rhinitis with allergic triggers is a year-round condition caused by household allergens like dust, mold, and animals kept as pets. Symptoms and treatment are the same as for allergic rhinitis, but sometimes an allergy test is needed to determine the triggers.
Treatment for rhinitis includes over-the-counter or prescription medication such as antihistamines and decongestants. Antihistamines are generally available over the counter and can relieve symptoms such as sneezing and watery eyes by blocking the histamines that are released by immune cells. These antihistamines tend to cause drowsiness. For this reason, antihistamines are sometimes combined with decongestants, which have stimulating side effects that counteract the drowsiness. However, decongestants can cause nervousness, restlessness, or insomnia, even while they relieve nasal congestion. Newer forms of antihistamines perform the same tasks as earlier ones, but do so without any sedating effects. These relatively new antihistamines are generally available by prescription and cost significantly more than earlier medications that are available over the counter. Recently, some new forms have become available over the counter as well. Intranasal corticosteroids may be used and cause fewer side effects than earlier antihistamines, but are less effective at treating watery and itchy eyes. Oral corticosteroids may be used on a limited basis (3 to 7 days) for more severe and treatment-resistant allergy symptoms. Allergen immunotherapy, or “allergy shots,” can be used in people who have yearly, recurrent, seasonal symptoms of long duration, or perennial symptoms. Allergy shots are not recommended for preschool-age children or the elderly because anaphylaxis can occur. Treatment is also not recommended for longer than 3 to 5 years.
When treating children for allergic rhinitis, nonpharmacological approaches, such as removing the allergen from the environment, are preferred. When this is not feasible, oral antihistamines and nonsteroidal intranasal treatments are the first-line therapy. The sedating effects of some antihistamines are sometimes beneficial for children, allowing them to sleep comfortably. Many later antihistamine medications have not been approved for use with children. Intranasal corticosteroids are effective in children, but some may have a temporary stunting effect on growth, and dosages should be small and monitored routinely.
With adults, precautions should be taken when using allergy medication with the elderly and those with high blood pressure. In the elderly, allergic symptoms are sometimes attributable to drug interactions or side effects of antihypertensive medication. Newer antihistamines that do not cause sedation or performance impairment should be considered. People with high blood pressure should be careful about using antihistamines and use only those medications approved for them.
In another form of allergy, there are two kinds of contact dermatitis: irritant and allergic. Both allergic and irritant contact dermatitis can vary in presentation from mild redness, itching, and chapping of skin to severe blistering and ulceration. Only a thorough history and skin patch testing can diagnose allergic contact dermatitis. Patch tests include strips of hypoallergenic tape to which allergens have been applied to the patient’s back and are removed after 48 hours. These test sites are evaluated for any reactions. Blood samples can also be used to check for antibody levels, but are not considered as accurate as patch testing. Blood testing is sometimes used in the case of allergic responses that are too severe to risk further exposure to the allergen.
Treatment of allergic contact dermatitis includes avoidance of the allergen as well as a course of prednisone, a steroid, for severe reactions. Prednisone is usually given as a higher initial dose and then tapered off over a period of time. Lower initial doses and more rapid tapering can lead to dramatic rebound of symptoms.
Food allergy is a reaction to something in a food or ingredient in a food, usually a protein. The eight most common food allergens—milk, eggs, peanuts, tree nuts, soy, wheat, fish, and shellfish—are thought to cause more than 90% of all allergic reactions to foods. Other foods have been found to be allergenic for individuals, but are less common. The National Institutes of Health estimated that 5% to 8% of children and 1% to 2% of adults have a true food allergy. Symptoms of food allergy vary from person to person and can also vary in the same person on different exposures. Symptoms can range from skin irritations such as rashes, hives, and eczema, to respiratory symptoms like runny nose, sneezing, and shortness of breath. In more severe cases, anaphylactic shock can occur. Symptoms of anaphylaxis usually appear rapidly and can include swelling of the throat, difficulty breathing, lowering blood pressure, and unconsciousness. Standard emergency care includes an injection of epinephrine and immediate medical attention for further evaluation.
Not all adverse reactions to foods are true food allergies; instead, they are food intolerances or food idiosyncrasies, which are generally localized and temporary and rarely lifelong. Food intolerance is an adverse reaction to a food or additive that involves digestion or metabolism but does not involve the immune system. An example is lactose intolerance, whereby a person lacks an enzyme needed to digest milk sugar. Food idiosyncrasy is an abnormal response to a food or food substance, but also does not involve the immune system. Sulfite sensitivity is an example.
At this point, the only way to treat food allergy is to avoid the food that causes the reaction. If a reaction occurs, then a person has several options of treatment, depending on the severity. Severe food allergy requires that the allergic person carry an epinephrine injection at all times in case of accidental ingestion or exposure. For less severe reactions, antihistamines or asthma inhalers are sometimes used to treat symptoms. Initial trials of vaccines to combat against allergic responses to certain foods are being conducted.
Allergies And Asthma
Although asthma and allergies do not always occur together, an estimated 70% to 75% of people with asthma have allergic triggers for their asthma. Asthma can be triggered by a host of different allergens and can trigger airway constriction, coughing, and wheezing.
It is currently unclear what, if any, psychological impact having allergies has on the average person. Many people who suffer from allergies treat their symptoms as needed and go on with their lives. Some people with severe, life-threatening allergies may experience extra stress because of their allergies and may suffer from increased anxiety. The phenomenon has been most studied in children, in whom there is some evidence of an increased association between allergies and some anxiety disorders, such as panic disorder. This evidence is in line with research showing that asthma is sometimes associated with an increased risk for anxiety disorders. As with any chronic illness, someone who is experiencing stress related to their illness may be helped by treating symptoms of anxiety.
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