Ragweeds are weeds that grow throughout the United States. They are most common in the Eastern states and the Midwest. A plant lives only one season, but that plant produces up to 1 billion pollen grains. Pollen-producing and seed-producing flowers grow on the same plant but are separate organs. After midsummer, as nights grow longer, ragweed flowers mature and release pollen. Warmth, humidity and breezes after sunrise help the release. The pollen must then travel by air to another plant to fertilize the seed for growth the coming year.

Ragweed plants usually grow in rural areas. Near the plants, the pollen counts are highest shortly after dawn. The amount of pollen peaks in many urban areas between 10 a.m. and 3 p.m., depending on the weather. Rain and low morning temperatures (below 50 degrees Fahrenheit) slow pollen release. Ragweed pollen can travel far. It has been measured in the air 400 miles out to sea and 2 miles up in the atmosphere, but most falls out close to its source.

These annual plants are easily overgrown by turf grasses and other perennial plants that come up from established stems every year. But where the soil is disturbed by streams of water, cultivation or chemical effects such as winter salting of roads, ragweed will grow. It is often found along roadsides and river banks, in vacant lots and fields. Seeds in the soil even after many decades will grow when conditions are right.

The job of immune system cells is to find foreign substances such as viruses and bacteria and get rid of them. Normally, this response protects us from dangerous diseases. People with allergies have specially-sensitive immune systems that react when they contact certain harmless substances called allergens. When people who are allergic to ragweed pollen inhale its allergens from air, the common hay fever symptoms develop.

Seventeen species or types of ragweed grow in North America. Ragweed also belongs to a larger family called Compositae. Other members of the family that spread pollen by wind can cause symptoms. They include sage, burweed marsh elder and rabbit brush, mugworts, groundsel bush and eupatorium. Some family members spread their pollen by insects rather than wind, and cause few allergic reactions. But sniffing these plants can cause symptoms.

Of Americans who are allergic to pollen-producing plants, 75 percent are allergic to ragweed. People with allergies to one type of pollen tend to develop allergies to other pollens as well.

People with ragweed allergy may also get symptoms when they eat cantaloupe and banana. Chamomile tea, sunflower seeds and honey containing pollen from Compositae family members occasionally cause severe reactions, including shock.

The allergic reaction to all plants that produce pollen is commonly known as hay fever. Symptoms include eye irritation, runny nose, stuffy nose, puffy eyes, sneezing, and inflamed, itchy nose and throat. For those with severe allergies, asthma attacks, chronic sinusitis, headaches and impaired sleep are symptoms.

To identify an allergy to ragweed or one of its relatives, requires a careful medical history, a physical exam and testing. The main approach to confirm a suspected allergy is the skin sensitivity test.

For this, the skin is scratched or pricked with extract of ragweed pollen. In sensitive people, the site will turn red, swollen and itchy. Sometimes blood tests are used to see if an antibody to ragweed is present. This is sometimes necessary, but it takes longer for processing by a laboratory and it is more expensive.

There is no cure for ragweed allergy. The best control is to avoid contact with the pollen. This is difficult given the amount of ragweed pollen in the air during pollination time. There is help, though.

• Track the pollen count for your area. The news media often reports the count, especially when pollen is high. You also can call the National Allergy Bureau at (800)-9-POLLEN, or reach it through the American Academy of Allergy, Asthma and Immunology on the Internet (www.aaaai.org). It will give you the pollen count for your region. Or visit www.Pollen.com to find the pollen count in your region of the country.
• Stay indoors in central air conditioning with a HEPA (high efficiency particulate air) filter attachment when the pollen count is high. This will remove pollen from the indoor air.
• Get away from the pollen where possible. People in the Eastern and Midwestern states may get some relief by going west to the Rocky Mountains and beyond. Going to sea or abroad in late summer can greatly reduce exposure. But check the area abroad you plan to visit. It may have a ragweed season as well. (See the Asthma and Allergy Answer article on, "Pollen and Mold Counts.")

You might even consider moving to get away from ragweed. Although this often helps people feel better for a short time, it is common for them to develop allergies to plants in the new location within a few years. A well thought out treatment plan is a better way to live with your allergies.

• Take antihistamine medications. These work well to control hay fever symptoms, whatever the cause. The drowsiness caused by older products is less of a problem with antihistamines now on the market. Antiinflammatory nose sprays or drops also help and have few side effects. Similar agents can reduce eye symptoms, but other remedies are needed for the less common, pollen-induced asthma.
• If medication does not give enough relief, consider immunotherapy ("allergy shots"). This approach reduces the allergic response to specific allergens. For it to work, the allergens must be carefully identified. The allergens are injected over several months or years. If diagnosis and treatment are well directed, you may see major improvements in symptoms.