Ingested vs. Contact vs. Inhaled Allergies

Medically reviewed by University of Illinois-Chicago, College of Medicine on January 28, 2016Written by Michael Kerr on May 4, 2012

An allergic response occurs when your immune system reacts abnormally to a common substance in the environment. That substance, known as an allergen, causes an inflammatory response in the body that may range from mild to life-threatening.

Allergies are a common problem all over the world, and the numbers of people affected go up every year. It’s believed that the increase in allergies is a result of pollution, genetic components, and 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 person has an abnormal immunologic reaction to food. Children are more commonly affected by food allergies than adults. Food allergies are most often caused by cow's milk, nuts, eggs, and fruit. 

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 food-specific 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
  • diarrhea
  • skin rash
  • swelling of the lips and eyes which appears and disappears quickly
  • anaphylaxis (a sudden, extreme allergic reaction characterized by difficulty breathing, swelling of the tongue or throat, which 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 with the skin.

Common irritants include:

  • soaps
  • detergents
  • hair dyes
  • jewelry
  • solvents
  • waxes
  • polishes

Natural allergens include poison oak, poison ivy, and ragweed.

Though annoying, a contact allergy is rarely dangerous.

Symptoms may include skin:

  • redness
  • itching
  • swelling
  • scaling
  • blistering 

The best way to deal with a contact allergy is to identify and avoid the irritant. 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. You should contact your doctor if there is drainage from a rash accompanied by pain or fever or if red streaks emanate from the rash. These are rather all signs of an infection.

Inhaled Allergies

Inhaled allergies are the most common type of allergy. Symptoms may include:

  • sneezing
  • runny nose
  • watery eyes
  • itchy eyes 

Many people who have inhaled allergies only experience symptoms during certain season. Pollen, grass, and mold are the most common triggers of seasonal allergies. 

Pollen is a fine powder that comes from tree, weeds, and grass. Each season, beginning in the spring and continuing through the fall, the amount of pollen in the air increases and may trigger allergic symptoms in people sensitive to pollen. Avoiding pollen 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. 

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 caused 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.

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