Allergies & Asthma: Causes and Diagnosis

What Causes Allergies?

The substances that cause allergic disease in people are known as allergens. "Antigens," or protein particles like pollen, food or dander enter our bodies through a variety of ways. If the antigen causes an allergic reaction, that particle is considered an "allergen." These can be:


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.

Unlike wind-pollinated plants, conspicuous wild flowers or flowers grown in most residential gardens are pollinated by bees, wasps, and other insects and therefore are not widely capable of producing allergic rhinitis.

Another culprit: house dust that can include dust mite particles, mold spores, cat and dog dander.


Frequent culprits include shrimp, peanuts and other nuts.


Such as medications delivered by needle like penicillin or other injectable drugs; venom from insect stings and bites.


Plants such as poison ivy, sumac and oak and latex are examples.


Like baldness, height and eye color, the capacity to become allergic is an inherited characteristic. But that doesn't make you automatically allergic to specific allergens. Several factors must be present:

  • Specific genes acquired from parents.
  • Exposure to one or more allergens to which you have a genetically programmed response.
  • 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.

On the other hand, poison ivy allergy (contact dermatitis) is an example of an allergy in which hereditary background does not play a part. Substances other than plants, such as dyes, metals, and chemicals in deodorants and cosmetics, can also cause a similar dermatitis.


If you break out in hives when a bee stings you, or you sneeze every time you pet a cat, you know what some of your allergens are. But if the pattern is not so obvious, try keeping a record of when, where, and under what circumstances your reactions occur. If the pattern still isn't clear, make an appointment with your doctor. Doctors diagnose allergies in 3 steps:

1. Personal and medical history. Your doctor will ask you questions to get a complete understanding of your symptoms and their possible causes. Bring your notes to help jog your memory. Be ready to answer questions about your family history, the kinds of medicines you take, and your lifestyle at home, school, and work.

2. Physical examination. If your doctor suspects an allergy, he/she will pay special attention to your ears, eyes, nose, throat, chest, and skin during the physical examination. This exam may include a pulmonary function test to detect how well you exhale air from your lungs. You may also need an X-ray of your lungs or sinuses.

3. Tests to determine your allergens. Your doctor may do a skin test, patch test or blood test.

  • Skin test. These are generally the most accurate and least expensive way to confirm suspected allergens. There are two types of allergen skin tests. In prick/scratch testing, a small drop of the possible allergen is placed on the skin, followed by lightly pricking or scratching with a needle through the drop. In intra-dermal (under the skin) testing, a very small amount of allergen is injected into the outer layer of skin. If you are allergic to the substance, you will develop redness, swelling, and itching at the test site within 20 minutes. You may also see a "wheal" or raised, round area that looks like a hive. Usually, the larger the wheal, the more sensitive you are to the allergen.
  • Patch test. This is a good test to determine if you have contact dermatitis. Your doctor will place a small amount of a possible allergen on your skin, cover it with a bandage, and check your reaction after 48 hours. If you develop a rash, you're allergic to the substance.
  • Blood tests. Allergen blood tests (also called radioallergosorbent tests [RAST], enzyme-linked immunosorbent assays [ELISA], fluorescent allergosorbent tests [FAST], multiple radioallergosorbent tests [MAST], or radioimmunosorbent tests [RIST]) are sometimes used when people have a skin condition or are taking medicines which interfere with skin testing. Your doctor will take a blood sample and send it to a laboratory. The lab adds the allergen to your blood sample, and then measures the amount of antibodies your blood produces to attack the allergens.
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