Ingested, Contact, Inhaled

An allergic response occurs when a person's immune system reacts abnormally to a common substance in the environment. That substance, known as an allergen, causes an inflammation response in the body that may range from mild to life-threatening. Worldwide, as many as 30 percent of people are afflicted with allergies and the numbers are growing.

According to the World Allergy Organization, allergies have become a major healthcare problem, with more than 250,000 preventable asthma deaths each year alone. Factors implicated in the increase in allergies include pollution, genetic components, and even improved hygiene.

Allergic reactions may be caused by a number of different allergens but are generally broken down into three categories: ingested allergies, contact allergies, and inhaled allergies.

Ingested allergies are caused when an offending allergen is eaten.

A contact allergy, also known as contact dermatitis, occurs when a substance such as a hair dye or detergent comes in contact with a person's skin.

The most common type of allergy—inhaled—is caused when a person breathes in an allergen such as pollen or animal dander.

Ingested Allergies

A food allergy—also known as food hypersensitivity—is a type of food intolerance in which a sufferer has an abnormal immunologic reaction to food.

It is estimated that between 220 and 520 million people worldwide suffer from food allergies, most of whom are children. Food allergies are most often caused by cow's milk, nuts, eggs, and fruit.

According to a recent North American study, 16 percent of children under the age of three have had a reaction to fruit or fruit juice, while 28 percent have had allergic reactions to other foods. Children with food allergies are more likely to have (or to develop) other allergies such as hay fever, rhinitis, and asthma.

Symptoms of food allergies can be mild, as is the case with hives (recurrent urticaria), which appear when certain foods such as strawberries are eaten. Most people with allergies have elevated levels of the immunoglobulin IgE in their bloodstreams. The IgE binds to the allergen and then attaches to mast cells in the skin. The mast cells in turn release histamine, which triggers a release of fluid that causes red, itchy, and inflamed skin—a condition called hives. More severe symptoms of ingested allergies may include abdominal cramps, vomiting, or diarrhea accompanied by a rash, swelling of the lips or eyes which appears and disappears quickly, or, in very rare cases, anaphylactic shock: a sudden, extreme allergic reaction that may result in death. Children with food allergies may exhibit behavioral signs such as crying, irritability, or milk refusal.

Contact Allergies

Contact allergies occur when an allergen touches a person's skin.

The symptoms of this type of allergy are usually confined to the area of contact.

Common irritants include soaps, detergents, hair dyes, jewelry, solvents, waxes, or polishes. Natural allergens include poison oak, poison ivy, and ragweed.

Though annoying, a contact allergy is rarely dangerous.

Symptoms may include redness, itching, swelling, scaling, or blistering. The best way to deal with a contact allergy is to identify and avoid the irritant. Short of that, treatments may include creams or ointments to help calm symptoms, antihistamines to prevent an allergic reaction, or, in the most serious cases, an anti-inflammatory medication such as prednisone. With treatment, contact allergies usually resolve in a few days. A person should contact his or her healthcare provider if there is drainage from a rash accompanied by pain or fever or if red streaks emanate from the rash. These are all signs of an infection.

Inhaled Allergies

Inhaled allergies are far and away the most common type of allergy. Hay fever (a hypersensitivity to pollen) alone affects more than 40 million Americans.

Each season, beginning in the spring and continuing through the fall, allergy sufferers curse the trees, weeds, and grasses responsible for their sneezing, runny noses and watery eyes. It isn't always as simple as retreating inside during allergy season either, as other types of airborne allergens such as fungi, mold, pet dander, and dust mites are prevalent indoors.

If things weren't bad enough for sufferers, a 2006 University of Cincinnati study found that exposure to certain fungi can make children more susceptible to developing other types of allergies as well, including asthma.

Many people confuse hay fever with asthma. Asthma, a chronic inflammatory disorder that causes bronchial swelling and constriction, may be triggered by hay fever if a person is unfortunate enough to have both conditions. But hay fever and asthma are very different. An asthma attack can be precipitated by a number of other factors, including a respiratory infection, certain drugs, other types of allergens such as dust mites or diesel fumes, and even cold air or an emotional response.

Exposure to pollutants, especially in developing nations, is associated with asthma, rhinitis, rhinoconjunctivitis, and acute respiratory infections, among other allergies and illnesses. In China alone, outdoor pollution is associated with over 300,000 deaths each year.