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Allergies
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An allergy is a hypersensitivity to a substance which is eaten, inhaled, brought in contact with the skin, or otherwise presented to the body. The body's manifestation of the hypersensitivity may vary from a mild temporary rash (urticaria) to anaphylactic shock and death.

The biology of hypersensitivity involves IgE, an immunoglobulin which may be found attached to basophils (a type of white blood cell) in the blood or in mast cells (an immune cell found in the body) near blood vessels. When the IgE detects a particular chemical in the allergen (the stuff that causes the allergy) it tells the attached cell to release histamine. Histamine is one of the body's signals that causes rashes, swelling, leakage of fluid from cells, and itching. Depending on where and how much histamine is released determines how the allergy is perceived. With asthma the allergen causes histamine release which constricts lung airways (bronchi).

With skin allergies, like some soap allergies or plant allergies, local skin redness (erythema), welts (urticaria), or itchiness may be the manifestation of the histamine release. Some people release massive amounts of histamine when presented with the allergen. Systemic anaphylaxis is the name given to this condition, where even a tiny amount of allergen may cause so much histamine release that severe breathing problems, diffuse soft tissue swelling in throat or body may be seen, and blood pressure may dramatically decrease possibly resulting in death.

Materials which have been known to cause anaphylactic reactions in humans include bee venom, penicillin, peanuts, various nuts, latex, shrimp, shellfish, and a variety of food additives and drugs. If someone develops anaphylaxis emergency care must be obtained immediately. Some people with known anaphylactic reactions will carry an injectable dose of epinephrine (Anakit, Epipen) to self administer epinephrine if they start to have an anaphylactic reaction. When emergency care arrives, oxygen and antihistamines will usually be given to the person with anaphylaxis. Skin testing can sometimes detect which substance causes the reaction.

Skin Allergies
With Skin allergies hypersensitivity in the skin may be rapid or slow. One type of hypersensitivity in the skin is called delayed hypersensitivity and may take days to show it's effect. Poison ivy contains an irritating oil which may cause redness and welts days after exposure. Urticaria is the medical name for red small raised welts which arise from release of histamine in the skin. Angioedema is a deeper more widespread type of swelling also from histamine release.
Exposure to animal fur, dander, mites, or ingesting certain allergy-provoking foods may cause the urticaria or angioedema to appear. Both are frequently associated with itching (pruritis). Some individuals may even develop welts just from local exposure to cold or mechanical abrasion. Another type of skin allergy is called "contact dermatitis," where redness, small blisters, and oozing may occur after direct skin contact with the allergen. This is most typical when a person is allergic to tape on their skin or to certain metal jewelry.

Skin allergies are coped with by avoiding the allergen once it is known and often with topical medications. Some topical medications include Benadryl, Calomine lotion (the pink stuff), hydrocortisone cream, or other steroid creams.

Allergic rhinitis
Allergic rhinitis is an allergic condition of the nose and sinuses characterized by runny nose, sneezing, watery eyes, and obstruction of the nasal passages. It may be associated with sinusitis, an inflammation of the sinuses which may be also allergy-mediated, but can be also seen with bacterial infections of the sinuses. Allergic rhinitis is often due to allergies to plant pollens or molds and is then called "hay fever" despite the fact that hay has nothing to do with it, and fever is rarely seen. Many sufferers of allergic rhinitis have other allergies such as eczema, urticaria, or asthma.
The most effective way to avoid allergic rhinitis is to learn the causative allergen and avoid it. Animal danders, animal fur, ragweed, and other pollens can be identified as causes. Avoiding moldy humid environments may decrease symptoms. Eliminating carpeting or frequently cleaning carpets may help. Using bleach to kill fungal growth in bathrooms is recommended. High efficiency particulate air filters (HEPA) may be needed with some cases of allergic rhinitis or asthma. There are now several nasal steroid sprays which are effective for treating allergic rhinitis. Cromolyn sodium, a powdered nasal spray is effective to prevent allergic rhinitis attacks.

Food Allergies
Food allergies are common but of varying severity. Allergies to cow's milk can be as mild as vague abdominal discomfort related to hypersensitivity to protein milk components. Lactose intolerance is not an actual allergy. Certain types of foods can cause anaphylactic shock in some people. Wheat, gluten, and other proteins in food may elicit allergic symptoms.
Food allergies may present differently than some other allergies. Swelling or itchiness at the lips may be seen. Asthmatic symptoms can occur. Stomach cramps, vomiting, and diarrhea can all be part of a food allergy reaction. Some food allergies are not intrinsic to the food material but are actually related to chemical additives. Allergies to food color have been documented. Sulfites are a class of anti-oxidants used to preserve some foods and wine. Allergies to sulfites have been documented and foods containing sulfites are usually marked.

Although heredity plays a part in the development of food allergies, studies have shown that babies which are exclusively breast-fed have less allergies than those given cow's milk and formulas. People with food allergies should avoid potentially dangerous foods.

Additional Information:
American College of Allergy, Asthma
NIH Allergy Site
Private-Practice Allergy Site
Am. Ac. of Allergy, Asthma, & Immunology

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