Allergies reflect an overreaction of the immune system to substances that usually cause no reaction in most individuals. These substances can trigger sneezing, wheezing, coughing and itching. Allergies are not only bothersome, but many have been linked to a variety of common and serious chronic respiratory illnesses (such as sinusitis and asthma). Additionally, allergic reactions can be severe and even fatal. However, with proper management and patient education, allergic diseases can be controlled, and people with allergies can lead normal and productive lives.

Common Allergic Diseases

The most common allergic diseases are:

• Allergic rhinitis (hay fever). Characterized by nasal stuffiness, sneezing, nasal itching, clear nasal discharge, and itching of the roof of the mouth and/or ears.
• Allergic asthma: Characterized by airway obstruction that is at least partially reversible with medication and is always associated with allergy. Symptoms include coughing, wheezing, shortness of breath or rapid breathing, chest tightness, and occasional fatigue and slight chest pain.
• Allergic Conjunctivitis: Characterized by inflammation of the eyes; it is the most common form of allergic eye disease. Symptoms can include itchy and watery eyes and lid distress. Allergic conjunctivitis is also commonly associated with the presence of other allergic diseases such as atopic dermatitis, allergic rhinitis and asthma.
• Urticaria (hives): A reaction of the skin, or a skin condition commonly known as hives. Characterized by the development of itchy, raised white bumps on the skin surrounded by an area of red inflammation. Acute urticaria is often caused by an allergy to foods or medication.
• Atopic Dermatitis (eczema): A chronic or recurrent inflammatory skin disease characterized by lesions, scaling and flaking; it is sometimes called eczema. In children, it may be aggravated by an allergy or irritant
• Contact Dermatitis: Characterized by skin inflammation; this is the most common occupational disease representing up to 40 percent of all occupational illnesses. Contact dermatitis is one of the most common skin diseases in adults. It results from the direct contact with an outside substance with the skin. There are currently about 3,000 known contact allergens.
• Sinusitis: Characterized by an inflammation of the sinuses, it frequently mimics the common cold. The symptoms of sinusitis persist for a longer period of time than a typical cold. Fever may develop or persist. Symptoms of sinusitis include frontal head discomfort, facial pain that often worsen when patients are bending or straining, and yellow or green nasal discharge.
• Otitis Media (middle ear infection): Characterized by inflammation of the middle ear and eardrum. A middle ear infection is the most common childhood disease requiring physician care. As many as half of children over three years of age with chronic otitis media have confirmed allergic rhinitis.
• Food Allergy: Most prevalent in very young children and frequently outgrown, food allergies are characterized by a broad range of allergic reactions. Symptoms may include itching or swelling of lips or tongue; tightness of the throat with hoarseness; nausea and vomiting; diarrhea; occasionally chest tightness and wheezing; itching of the eyes; decreased blood pressure or loss of consciousness and anaphylaxis.
• Latex Allergy: An allergic response to the proteins in natural, latex rubber characterized by a range of allergic reactions. Persons at risk include healthcare workers, patients having multiple surgeries and rubber-industry workers. Symptoms include hand dermatitis, eczema and urticaria; sneezing and other respiratory distress; and lower respiratory problems including coughing, wheezing and shortness of breath.
• Insect Sting Allergy: Characterized by a variety of allergic reactions; stings cannot always be avoided and can happen to anyone. Symptoms include pain, itching and swelling at the sting site or over a larger area and can cause anaphylaxis. Insects that sting include bees, hornets, wasps, yellow jackets, and fire and harvest ants.
• Drug Allergy: Characterized by a variety of allergic responses affecting any tissue or organ. Drug allergies can cause anaphylaxis; even those patients who do not have life-threatening symptoms initially may progress to a life-threatening reaction.
• Anaphylaxis: Characterized by life-threatening symptoms. This is a medical emergency and the most severe form of allergic reaction. Symptoms include a sense of impending doom; generalized warmth or flush; tingling of palms, soles of feet or lips; light-headedness; bloating and chest tightness. These can progress into seizures, cardiac arrhythmia, shock and respiratory distress. Possible causes can be medications, vaccines, food, latex, and insect stings and bites.

(For more detailed information on these allergies, see the Asthma and Allergy Answer articles on these topics.)

Important Causes of Allergy

The substances that cause allergic disease in susceptible people are known as allergens. They enter our bodies in a variety of ways:

• Inhaled into the nose and the lungs. Examples are airborne pollens of certain trees, grasses and weeds; house dust that include dust mite particles, mold spores, and cat and dog dander.
• Ingested by mouth. Frequent culprits include shrimp, peanuts and other nuts.
• Injected, such as reactions to penicillin, several other injectable drugs, and stinging insect venom.
• Absorbed through the skin: poison ivy, sumac and oak.

Plant pollens that are carried by the wind cause most allergies of the nose, eyes and lungs. These plants (including certain weeds, trees and grasses) are natural pollutants produced at various times of the year when their small, inconspicuous flowers discharge literally billions of pollen particles.

Because the particles can be carried significant distances, it is important for you not only to understand local environmental conditions, but also conditions over the broader area of the state or region in which you live. Unlike the wind-pollinated plants, conspicuous wild flowers or flowers used in most residential gardens are pollinated by bees, wasps, and other insects and therefore are not widely capable of producing allergic disease.

Like baldness, height and eye color, the capacity to become allergic is an inherited characteristic. Yet, although you may be born with the genetic capability to become allergic, you are not automatically allergic to specific allergens. Several factors must be present for allergic sensitivity to be developed:

• The specific genes acquired from parents.
• The exposure to one or more allergens to which you have a genetically programmed response.
• The degree and length of exposure.

A baby born with the tendency to become allergic to cow's milk, for example, may show allergic symptoms several months after birth. A genetic capability to become allergic to cat dander may take three to four years of cat exposure before the person shows symptoms. These people may also become allergic to other environmental substances with age.

On the other hand, poison ivy allergy (contact dermatitis) is an example of an allergy in which hereditary background does not play a part. The person with poison ivy allergy first has to be exposed to the oil from the plant. This usually occurs during youth, when a rash does not always appear. However, the first exposure may sensitize or cause the person to become allergic and, when subsequent exposure takes place, a contact dermatitis rash appears and can be quite severe. Many plants are capable of producing this type of rash. Substances other than plants, such as dyes, metals, and chemicals in deodorants and cosmetics, can also cause a similar dermatitis.

Correctly Diagnosing Allergies

A number of diseases can appear to be allergic but upon professional examination prove not to be so. For example, you may have nasal symptoms that are due to chronic and repeated infections and have symptoms similar to allergic rhinitis.

Some people with asthma lack allergies to any substance. It is important therefore to show proof of allergy whenever it is suspected because the treatments for allergic and non-allergic disease can be quite different.

Treatment Choices

Self-improvement. Some people with allergic disease caused by airborne allergens improve by themselves. This can happen for a few reasons:

• They relocate to an area where the allergen(s) causing their illness is not found.
• Their tolerance to the allergen(s) increases through activation of normal, protective immunologic mechanisms.

Interventions. There are several approaches for controlling allergy by reducing or eliminating symptoms:

• Avoiding the offending allergen. This may involve such measures as remaining within a well air-conditioned home or building as much as possible during the peak pollen seasons, learning to recognize and avoid
• poison ivy, avoiding certain foods, instituting environmental controls that protect you from house dust mites and animal dander.
• Taking medications, either prescribed or over-the-counter, which counteract the reaction and reduce or eliminate the symptoms. Numerous medications are available and relief is possible for many people.
• Being immunized against allergens to which you are allergic with allergy injection therapy. Although this is extremely helpful for certain people, this form of therapy is usually reserved for more severe cases or for persons in whom other forms of treatment have not been successful. Whether or not allergy injection therapy in patients with hay fever prevents them from developing asthma later in life remains unknown.