Disorder
| Symptoms
| Common allergens or other causes
| Main disease mechanism
| Other key features
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Allergic rhinitis: | Blocked, runny nose, sneezing, itching and streaming eyes
| | IgE-mediated
| Mild winters and warmer springs mean that pollination in the United Kingdom now starts earlier than it did 50 years ago. Therefore symptoms can be well established by the first week in May and peak around mid-June to early July. When pollen counts are very high, some wheeziness can also coexist with rhinitis, in a condition known as seasonal allergic asthma
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- Seasonal allergic rhinitis (hayfever or rhinoconjunctivitis)
| Worst symptoms occur at the height of summer when vast clouds of grass pollens become airborne
| Pollen (commonly grass, but also tree and weed pollen)
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- Perennial allergic rhinitis
| Chronic symptoms occur all year round
| Housedust mite, allergens derived from cats, dogs, horses and pet rodents. In some patients, perennial rhinitis is due to non-allergic causes such as infection or structural abnormalities of the airway. A small minority of patients also have underlying immunodeficiency problems
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Asthma | Characterised by episodes of wheezy breathlessness, but may also present as an isolated cough, particularly in children. "Non-atopic" asthma often starts later in life and can be more severe
| The cause is still uncertain, and it is often difficult to determine the role of allergy. Allergy to housedust mite, pollen, moulds and pets can trigger an attack in a significant proportion of patients; food allergens and additives may rarely trigger symptoms. A significant proportion of patients are not sensitised to allergens so are "non-atopic" or "intrinsic" asthmatics
| IgE-mediated | Pathology involves inflammation and muscular contraction of the large and small airways (bronchi and bronchiolessee Figure 2). The consequence is an irritable, easily constricted airway in which a variety of non-specific irritants causes airflow obstruction (bronchial hyper-responsiveness). Triggers include viral infection, exercise, certain drugs, and exposure to fumes or tobacco smoke
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Anaphylaxis: | Anaphylaxis describes a group of symptoms affecting several parts of the body, caused by a hypersensitivity reaction to an allergen in a previously sensitised individual. "Anaphylactic shock" is an extreme hypersensitive reaction characterised by an overwhelming sense of impending doom, a dramatic fall in blood pressure, swelling in the throat and mouth, chest tightness, breathlessness from severe asthma and unconsciousness. In a small number of cases, anaphylactic shock results in death
| | IgE-mediated
| A rash may herald that a more severe reaction will occur in the future, but in some cases anaphylactic shock occurs without any previous warning
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- Sensitivity to insect venom
| Some reactions are life-threatening but most result in a temporary irritation or swelling around the site of the sting
| Can be caused by wasp or bee stings
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| Rash anywhere in the body
| Almost any drug, but the most common causes are penicillin and other betalactam antibiotics
| | Only a small proportion of adverse drug reactions have an allergic background, and an even smaller proportion are IgE-mediated
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| Rash anywhere in the body, especially around the mouth and throat
| Peanuts, tree nuts (such as almonds, hazelnuts, walnuts and brazil nuts), milk, eggs, fish and shellfish
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Oral allergy syndrome | Swelling in the lips, mouth, tongue or throat
| Occurs in tree, grass, weed and latex allergy sufferers immediately after contact with certain foods. A significant proportion of people who are allergic to birch trees, suffer oral allergy syndrome after eating raw apples
| IgE-mediated |
The reaction is caused by a cross-reaction between the allergen to which the patient is sensitised, and the food protein
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Urticaria and Angioedema: | Itching and swollen, red welts known as "hives" or "wheals" on the surface of the skin (urticaria) or deeper in the skin, particularly around the mouth and eyes (angioedema)
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| Rash suddenly occurs and usually disappears within 24-48 hours
| Food allergy, especially to peanuts, tree nuts or shellfish. Viral infection is more commonly the cause than food allergy
| IgE-mediated |
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| Symptoms last intermittently or continuously for more than three months, but often clear up without treatment
| Underlying cause is rarely found
| Non-IgE-mediated |
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Atopic dermatitis (Atopic eczema) | Chronic, recurrent inflammation of the skin, characterised by intense itching which particularly affects the flexures (creases of skin) at joints such as the wrists, elbows, ankles and knees
| Egg or cow's milk allergy sometimes triggers symptoms in children, but this is rarely the case in adults. A number of external influences may trigger or exacerbate symptoms, including emotional stress, irritation of the skin by wool or nylon, infections and vaccinations
| IgE-mediated | Patients often also suffer from other atopic disorders such as allergic rhinitis, asthma or both. It is currently thought that atopic dermatitis usually develops first and this then predisposes an individual to the production of IgE and the development of other atopic disorders
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Contact dermatitis | Redness, scaling and itching at sites of exposure to the irritant. Can lead to thickening of the skin (lichenification)
| Most commonly due to an irritation caused by external substances, but may also result from non-atopic allergic sensitisation to substances in the workplace, or nickel, lanolin and cosmetics
| Non-IgE-mediated |
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Extrinsic allergic alveolitis (EAA): e.g. |
Shortness of breath, with or without cough, and in the acute phase there are usually muscular aches, fever and a lack of energy
| Repeated or prolonged exposure to agents found in bacteria, animal products and chemicals
| Non-IgE-mediated | EAA describes a group of lung disorders caused by an inflammation of the alveoli (air sacs in the lung)
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| | Bacteria found in straw, mouldy hay or grain
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| | Bird droppings and feathers
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| | Dried urine, hair or animal dander
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Coeliac disease | Diarrhoea, failure to thrive (in infants and children), weight loss (in adults) and fatigue
| Caused by an allergy to gliadin, a protein found in wheat, barley and rye
| Non-IgE-mediated | Occurs in genetically predisposed individuals at all ages after infancy. It is an allergic disorder although the basic mechanism is autoimmune. Management requires a lifelong gluten-free diet
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