Of all the things that can cause an allergy, pollen is one of the most common. Many of the foods, medicines, or animals that cause allergies can be avoided to a great extent. Even insects and household dust are escapable. But short of staying indoors, with the windows closed, when the pollen count is high-and even that may not help-there is no easy way to avoid airborne pollen.

What is pollen?

Plants produce tiny, microscopic -too tiny to see with the naked eye-round or oval pollen grains to reproduce. In some species, the plant uses the pollen from its own flowers to fertilize itself. Other types must be cross-pollinated. Cross-pollination means that for fertilization to take place and seeds to form, pollen must be transferred from the flower of one plant to that of another of the same species. Insects do this job for certain flowering plants, while other plants rely on wind for transport.

The types of pollen that most commonly cause allergic reactions are produced by the plain-looking plants (trees, grasses, and weeds) that do not have showy flowers. These plants make small, light, dry pollen grains that are custom-made for wind transport.

Amazingly, scientists have collected samples of ragweed pollen 400 miles out at sea and 2 miles high in the air. Because airborne pollen can drift for many miles, it does little good to rid an area of an offending plant. In addition, most allergenic pollen comes

from plants that produce it in huge quantities. For example, a single ragweed plant can generate a million grains of pollen a day.

The type of allergens in the pollen is the main factor that determines whether the pollen is likely to cause hay fever. For example, pine tree pollen is produced in large amounts by a common tree, which would make it a good candidate for causing allergy. It is, however, a relatively rare cause of allergy because the type of allergens in pine pollen appear to make it less allergenic.

Among North American plants, weeds are the most prolific producers of allergenic pollen. Ragweed is the major culprit, but other important sources are sagebrush, redroot pigweed, lamb’s quarters, Russian thistle (tumbleweed), and English plantain.

Grasses and trees, too, are important sources of allergenic pollens. Although more than 1,000 species of grass grow in North America, only a few produce highly allergenic pollen.

It is common to hear people say they are allergic to colorful or scented flowers like roses. In fact, only florists, gardeners, and others who have prolonged, close contact with flowers are likely to be sensitive to pollen from these plants. Most people have little contact with the large, heavy, waxy pollen grains of such flowering plants because this type of pollen is not carried by wind but by insects such as butterflies and bees.

When do plants make pollen?

One of the most obvious features of pollen allergy is its seasonal nature-people have symptoms only when the pollen grains to which they are allergic are in the air. Each plant has a pollinating period that is more or less the same from year to year. Exactly when a plant starts to pollinate seems to depend on the relative length of night and day-and therefore on geographical location- rather than on the weather. On the other hand, weather conditions during pollination can affect the amount of pollen produced and distributed in a specific year. Thus, in the Northern Hemisphere, the farther north you go, the later the start of the pollinating period and the later the start of the allergy season.

A pollen count, familiar to many people from local weather reports, is a measure of how much pollen is in the air. This count represents the concentration of all the pollen (or of one particular type, like ragweed) in the air in a certain area at a specific time. It is shown in grains of pollen per square meter of air collected over 24 hours. Pollen counts tend to be the highest early in the morning on warm, dry, breezy days and lowest during chilly, wet periods. Although the pollen count is an approximate measure that changes, it is useful as a general guide for when it may be wise to stay indoors and avoid contact with the pollen.

Many people think that pet allergy is provoked by the fur of cats and dogs. Researchers have found, however, that the major allergens are proteins in the saliva. These proteins stick to the fur when the animal licks itself. Therefore, often it is pet dander, the skin flakes shed from an animal’s body similar to dandruff or pet pollen, that bears this allergy-causing saliva and triggers allergic reactions in people.

Urine is also a source of allergy-causing proteins, as is the skin. When the substance carrying the proteins dries, the proteins can then float into the air. Cats may be more likely than dogs to cause allergic reactions because they lick themselves more, may be held more, and spend more time in the house, close to humans.

Some rodents, such as guinea pigs and gerbils, have become increasingly popular as household pets. They, too, can cause allergic reactions in some people, as can mice and rats. Urine is the major source of allergens from these animals.

Allergies to animals can take 2 years or more to develop and may not decrease until 6 months or more after ending contact with the animal. Carpet and furniture are a reservoir for pet allergens, and the allergens can remain in them for 4 to 6 weeks. In addition, these allergens can stay in household air for months after the animal has been removed. Therefore, it is wise for people with an animal allergy to check with the landlord or previous owner to find out if furry pets lived on the premises.

While general blood tests give a picture of your overall health, specific allergy related blood tests can measure levels of immunoglobulin E (IgE), a key antibody that’s released during an allergic reaction.  While everyone’s body produces IgE, people who have allergies make larger quantities of this protective protein.

A blood test called RAST (radioallergosorbent) measures the levels of specific allergy related substances in your blood.

Blood testing for allergies is another good option particularly if:

• You cannot suspend antihistamine therapy which may inhibit skin tests;
• You are so sensitive to the allergen that the test might be risky;
• You have widespread skin disease making skin testing difficult; or
• If your skin cannot be skin tested for some other reason.

One problem with both blood and skin tests for food allergies is they are highly sensitive. So if you do have any remote or slight food allergy, the tests are likely to catch it. However, the tests are not specific enough. This means that the tests often are positive even when there is no significant food allergy.

Additionally, your physician may have you perform “use or elimination testing,” which is often used to check for food or drug allergies. Here, you will simply have to avoid certain items to see if you get better, or use suspected items to see if you feel worse.

• The results are available immediately
• They can be more sensitive to subtle allergies
• They are less expensive

What are the different allergy skin tests?

1. Scratch (Puncture or Prick) Test

First, your health care provider examines the skin either on your forearm or back and cleans it with alcohol. Next, areas on your skin are marked with a pen to identify each allergen to be tested. A drop of extract for each potential allergen is placed on the corresponding mark. Now, a small disposable pricking device is used to prick the skin so the extract can enter into the outer skin layer. The skin prick is not a shot and does not cause bleeding. Lastly, the skin is closely watched for signs of a reaction, which include swelling and redness. Often such reactions occur in as little as 15 minutes.

2. Intradermal Test

First, your health care provider examines the skin either on your forearm or back and cleans it with alcohol. Then a small amount of the allergen is injected just under the skin. Lastly, you must wait about 15 minutes to see how your skin reacts.

3. Patch Test

The allergen is applied to a patch that is then placed on the skin. Sometimes, this is done to pinpoint a trigger of allergic contact dermatitis. If there are IgE’s (allergic antibodies) in your body, your skin will become irritated and may itch. This reaction means you are allergic to that substance. Patch tests take approximately 48 hours (do not bathe or swim while wearing these patches). You must return to your physician to determine whether your skin has reacted to the allergens.

Before your skin allergy test, your doctor will give you a list of medications to be avoided before the test since those drugs may interfere with the test. Specifically, allergy medicines, including over-the-counter antihistamines, stop allergic reactions, so you should not take them for 48 hours before the test. Speak to your doctor about discontinuing any allergy medicines or other medications prior to the test.

To diagnose allergies, a thorough health history review and physical examination with a physician is a great first step. If you have allergy symptoms that occur in association with exposure to certain things, that is highly significant, so make sure you tell your doctor about the association.

Allergy diagnostic tests, such as skin or blood tests, provide similar information and may confirm what your health history tells the doctor. If you and your doctor were to rely exclusively on the results of skin or blood tests (without information about your medical history and physical examination), you may potentially be misdiagnosed with having an allergy problem that you may not necessarily have.