Pollens are round or oval microscopic particles that act as engines for plant fertilization. In some cases, a plant uses the pollen in its own flower to fertilize itself. In other cases, one plant produces the pollen that fertilizes another plant of the same species, a process known as cross-pollination. Without pollens, plants could not reproduce.

In cross-pollination, the pollen must travel from one plant to another. Sometimes a host carrier delivers pollens to their eventual destination, such as when bees carry pollens from one flower to another. These types of pollen, usually from bright flowers, usually do not cause allergies. However, lighter pollens (from weeds, grass and trees) are carried by the wind to mate with their female counterparts.

These types of pollens have less desirable consequences for some humans. For millions of people, contact with certain types of pollen triggers the itchy eyes, runny nose, sneezing and nasal congestion associated with allergies.

Individual pollens are only active during certain times of the year. People who suffer from pollen-based allergies are likely to experience their symptoms during these same periods year after year.

Many who suffer from pollen-based allergies can minimize their symptoms by adjusting their activity schedule based on pollen counts. Those with more severe symptoms may have to seek medical help in alleviating their symptoms.

Pollens are tiny protein particles that carry the male gametes (sperm) that combine with female gametes (eggs) in plant fertilization. Pollination occurs with the movement of pollen from the anther of one flower to the stigma of the same flower or another flower.

Plants pollinate at the same time each year. Some plants pollinate in the spring, while others pollinate in the late summer or early fall. Pollination appears to be affected by the relative length of night and day, so geographical location is the key factor. Generally, the farther north, the later in the season a plant will pollinate.

In the United States, trees generally pollinate in February through May, grasses pollinate in May through June, and flowering plants and weeds pollinate throughout the summer and until the first frost.

Pollen seasons in the United States are roughly as follows:

Grass pollen season:

• Southeast and Southwest: March to October
• South: April to September
• Northeast, Northwest, Midwest and Great Plains: May to August

Ragweed pollen season:

• Florida and extreme southern Georgia: July to November
• Deep South: August to November
• Northwest: No season
• Rest of the nation: August to October

Tree pollen season:

• Bottom third of nation: January to June
• Middle third of nation and Northwest: February to June
• Top third of nation: March to June

Weed pollen season:

• Florida, and parts of George, Alabama, Arizona, Nevada and California: April to November
• Northwest and parts of California, Nevada, Idaho, Utah and Arizona: June to October
• Deep South: July to November
• Rest of nation: July to October

The amount of pollen produced and distributed in a given season depends on climate conditions, including wind currents, humidity and rainfall. This is why pollen counts can vary within cities and even during the day. For instance, pollen counts are usually lowest during wet, chilly periods and in the evening hours. They tend to be highest in the mornings, and on warm, dry, windy days.

In the United States, an estimated 20 percent of the population suffers from seasonal allergies, according to the American Academy of Allergy, Asthma and Immunology.

Pollens cause allergies when they lodge inside the mucous membranes that line an individual’s nasal cavities. The white blood cells of the body’s immune system react to this presence by producing the antibody immunoglobulin E (or IgE), which attaches to mast cells in the tissues. When the antibody comes into contact with the pollen (the antigen) again, it triggers a process that results in the release of histamine, leukotrienes and other chemical substances.

These chemicals open the small blood vessels of the nose, causing fluids to leak through the expanded vessel walls and triggering swelling in the nasal passages. The result is nasal congestion and the other symptoms (e.g., watery eyes, itchy nose) of the allergic reaction commonly known as hay fever (medically known as allergic rhinitis).

Not all humans react in the same way to these allergens. For example, a nonallergic person might produce only very small amounts of IgE when confronted by an allergen. In these people, mucus in the airway simply sweeps pollen to the throat, where it is swallowed or coughed out.

The type of pollen can determine whether or not people will be allergic to them. Many of the pollens that cause hay fever come from weeds, trees and grasses. These pollens are comparatively smaller, lighter and drier than other types and are carried easily by the wind.

Heavier pollens, such as the large, waxy pollens found in roses, are carried by insects from flower to flower. Because of their size, fewer can be carried by the wind and they are therefore less likely to cause an allergic reaction in most people. However, people who have prolonged, close contact with colorful and/or scented flowers, such as florists, are more likely to develop allergies to these plants.

Pollens that are most likely to cause allergies in the general public include the following:

The symptoms of pollen-related allergies are numerous. Most people are likely to have their first symptoms before age 30, though others develop pollen-related allergies later in life. Symptoms include:

• Sneezing
• Itchy, runny nose
• Nasal congestion
• Cough
• Itchy or sore throat
• Red, itchy or watery eyes

Individuals who suspect a pollen allergy can confirm the diagnosis by visiting an allergist/immunologist. In order to establish if an allergy is present, the physician will collect the patient’s medical history and perform a physical examination.

Physicians look for several signs in determining whether a person is suffering from hay fever or other pollen-related allergies. These include:

• Inflammation of eyes, nose and throat
  
  
• Pale pink or bluish and swollen lining of the nose
  
  
• Dark circles under the eyes (also known as allergic shiners)
  
  
• Wrinkles under the eyes (due to chronic puffiness)
  
  
• Crease across the nose (also known as the allergic salute, it is the result of pushing the nose upward when rubbing it to relieve the itching associated with allergies)

Physicians also can perform skin testing to narrow the cause of symptoms to a specific allergen. During skin testing, a doctor will prick or inject a specific allergen into a patient’s skin and wait for 10 to 20 minutes to see if there is a reaction. The development of a small, raised, reddish area generally indicates a positive reaction.

Skin testing is not practical for those with skin conditions. In such cases, a blood test such as a radioallergosorbent test (RAST) may be the best way to measure whether or not an individual is allergic to a certain pollen. In this process, an allergen is introduced and a patient’s blood is checked for an increase of the IgE antibody, which indicates a potential allergy.

Once the specific pollen causing the symptoms is identified, the physician can help the patient determine when the allergen is most prevalent. The physician can also provide tips to help the patient minimize contact with the allergen.

With pollen allergies, the only sure way for a patient to prevent an allergic reaction is to avoid any contact with the pollen allergen to which they are sensitive (avoidance). However, this is not always possible. Since millions upon millions of pollen grains float through the air, they can be found almost everywhere, both outdoors and inside. Samples of ragweed pollen have been detected far out in the ocean and up to 2 miles above the earth.

However, there are some steps people can take to cut down their exposure to pollens, including:

• Use air conditioning, which cleans and dries out air. Also change the filter in the air conditioning unit often.
  
  
• Use air-filtering devices that can be added to heating or cooling systems, such as HEPA filtration.

  

• Limit outdoor activities during high pollen counts, and windy and humid days.
  
  
• Keep home and car windows closed.
  
  
• Wash hands and rinse eyes after going indoors.
  
  
• Shower or bathe before bedtime to wash pollens from hair and skin.
  
  
• Wear eyeglasses or sunglasses when outside.
  
  
• Try to avoid mowing the lawn, weeding or raking leaves, as these stir up pollen spores. If you must engage in these activities, try to wear special allergen-proof masks. Some forms of gardening may be possible for people with pollen allergies. Many types of pollen associated with gardening are of the waxy, heavy type that do not easily travel into the human airway. However, people with pollen allergies should be careful to stick to plants that are not highly allergenic. Apple trees and rose bushes are examples of plants that do not cause problems for most people.
  
  
• Do not hang laundry outside because pollens can collect on fabrics.
  
  
• Keep your pets clean to minimize the amount of pollen particles they bring inside.

The amount of pollen in the air at any given time varies dramatically based on the time of the year, the temperature and the amount of rainfall. A good way to minimize exposure to allergenic pollens is to keep an eye on the latest pollen count and modify behavior accordingly. Individuals with pollen allergies should avoid spending time outdoors and exposing themselves to allergens when the pollen count is high. Pollen levels tend to be highest in the morning, and on sunny or windy days.

Most local weather forecasts during high-pollen seasons will include a report on the levels of pollens in the air on a given day. This summary can be helpful in planning outdoor activities for people with pollen allergies. Reports are also provided through toll-free telephone numbers and on various Web sites on the Internet.

Those who must remain outdoors can protect themselves against high levels of pollen by wearing face masks designed to filter out the allergen before it reaches the nasal cavity. Over-the-counter antihistamines can relieve sneezing, a runny nose and itchy, watery eyes. Meanwhile, nasal decongestants can reduce stuffiness. Patients are advised to consult their physicians before taking any over-the-counter or prescription medications.

Medical or prescription solutions may be necessary for those with more severe pollen-related allergies. A corticosteroid nasal spray is a prescription drug that is designed to clear hay fever symptoms. Patients who use these sprays report few of the side effects associated with corticosteroids taken by mouth or by injection. The spray must be used daily.

Mast cell stabilizers are other medications available as both a nasal spray and in eyedrop form. These drugs decrease the sensitivity of mucus membranes to allergens.

The U.S. Food and Drug Administration (FDA) has approved a type of leukotriene modifier for prevention of hay fever symptoms. This drug prevents the chemical substance known as leukotrienes from promoting inflammation. Unlike other medications designed to relieve the symptoms of hay fever, leukotriene modifiers are daily medications taken to prevent the chemical reaction that produces symptoms.

Allergy shots (immunotherapy) may increase an individual’s tolerance to an allergen and prevent the frequency of symptoms. These shots contain a small amount of the allergen and may be given on a regular schedule, such as once or twice a week for several years. Some physicians choose to give the shots less often, and space out the time between shots. If the individual shows no adverse reaction, the amount of allergen is increased with each successive injection. Over time, the body’s immune system learns not to react to the presence of the allergen. However, these injections are not always successful in treating the allergy.

When allergy shots do work for an individual, they are often very effective – particularly when treating pollen allergies. Recent studies have shown that pollen immunotherapy, when used consistently for three to five years, often remains effective for more than five years after discontinuation of the shots.

Researchers continue to explore new treatments for preventing or relieving allergy symptoms. One of the most promising new treatments is a pollen-blocking cream that patients apply to the inside of their nose. A recent study indicates that those using the cream experienced a 20 percent increase in nasal airflow. This cream is not yet available in the United States.

Nasal filters (thin mesh screens worn in each nostril) have shown early success in preventing allergic rhinitis symptoms. This product is currently being evaluated in U.S. clinical trials and may be available sometime in the future. An allergy shot therapy that is targeted to specific types of grass pollen has also shown recent promise and is being further studied. A new ragweed vaccine is also showing promise. It was effective for a year or longer in early trials.  

Preparing questions in advance can help patients to have more meaningful discussions with their physicians regarding their conditions. Patients may wish to ask their doctor the following questions related to pollen:

1. Do my symptoms indicate a pollen allergy?
   
   
2. What methods will you use to determine if I am allergic to pollen?
   
   
3. What type of pollen am I allergic to?
   
   
4. Does my pollen allergy pose a risk to my overall health?
   
   
5. What are my treatment options? How effective are they?
   
   
6. Am I a candidate for allergy shots?
   
   
7. At what time of year am I most likely to experience symptoms?
   
   
8. What steps can I take to prevent symptoms?
   
   
9. Where can I find local pollen counts?
   
   
10. Are my children more likely to develop pollen allergies because I have the condition?