Also called: Ambrosia Artemisiifolia, Horse Ragweed, Common Ragweed, Ambrosia Trifida, Great Ragweed
Millions of Americans are affected by seasonal allergies, the most common of which is ragweed allergy. Ragweed allergy occurs when sensitive people react to pollen from the ragweed plant. People with this type of allergy experience symptoms after coming into contact with the pollen – usually by inhaling pollen particles.
Ragweed pollen acts as an allergen in sensitive people. An allergen is a harmless substance that the body recognizes as a threat, triggering an exaggerated reaction from the immune system. Symptoms, such as itchy eyes, nose and throat, runny nose and sneezing, are the result of such an allergic reaction. The allergic reaction to plants that produce pollen is known as hay fever (allergic rhinitis).
Each ragweed plant is capable of producing billions of pollen particles every year. The pollen is distributed by air currents that allow the plant to disperse its pollen to other ragweed plants. Ragweed pollen can travel hundreds of miles in the air, triggering symptoms associated with allergic rhinitis. Because ragweed pollinates in late summer to fall, depending on the region, allergy symptoms tend to appear seasonally in affected people.
Ragweed is widely distributed throughout the United States and people sensitive to this plant should track the pollen counts in their region to be aware of the timing of ragweed pollination in their area.
By keeping track of pollen forecasts, people can take measures to avoid exposure (staying indoors when ragweed counts are high, for instance) or minimize symptoms (such as taking certain allergy medications prior to the onset of symptoms).
Ragweed allergy can be diagnosed by consulting a physician. The physician will examine the patient and develop a medical history. A skin test may be used to determine the specific allergen that is triggering the patient’s symptoms. The physician may recommend against the planting of related plants in the patient’s garden, and warn about cross-reactivity with certain foods. Ragweed allergy can also be treated with medications such as antihistamines, nasal decongestants, corticosteroids and allergy shots.
Ten to 20 percent of Americans have seasonal allergies, and 75 percent of them are allergic to ragweed, according to the Asthma and Allergy Foundation of America. Ragweed allergy is the most common type of pollen allergy in the United States.
Ragweed is a weed that grows throughout the United States, often in soil disturbed by cultivation or along roadways. There are many different types of ragweed, including one that grows to be over 15 feet high. In the United States, they are most common in the Eastern states, the South and the Midwest.
Ragweed produces highly allergenic pollen, causing widespread cases of hay fever (allergic rhinitis) and asthma attacks. Most allergic people are likely to have their first symptoms before age 30, though others develop ragweed-related allergies later in life.
Ragweed is an annual plant, which means that the plant lives for only one season, so therefore it produces large quantities of pollen. Both the pollen and seed-producing flowers grow on the same plant. Each plant produces up to 1 billion grains of pollen. Pollens are tiny protein particles that carry the male gametes (sperm), which 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.
After mid-summer, the ragweed flowers mature and release the pollen grains. The pollen is carried through the air to another ragweed plant to fertilize the seed for the following year. Because of their light weight, grains are capable of traveling up to 400 miles from their source, though most of the pollen typically lands within in few miles of its source. Ragweed seeds are very hardy and can grow in the right conditions even after many decades of lying dormant.
Plants pollinate at the same time each year. Pollination appears to be affected by the relative length of night and day, so geographical location is a key factor. Generally, the farther north, the later in the season a plant will pollinate. Ragweed generally pollinates beginning in late summer and pollen amounts usually peak in the fall.
Ragweed pollen season:
- Florida and extreme southern Georgia: July to November
- Rest of the nation: August to November
Most pollen disappears when the temperature drops to the 40s (4 to 9 degrees Celsius), and patients generally begin to feel relief from their symptoms at that time.
The amount of ragweed pollen produced and distributed in a given season depends on climate conditions, including wind currents, humidity and rainfall. This is why ragweed pollen counts can vary within cities and even during the day. For instance, ragweed 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.
Ragweed pollens cause allergies when the pollen grains become airborne and lodge inside the mucous membranes that line an individual’s nasal cavities. The result is symptoms such as nasal congestion, watery eyes and itchy nose.
However, not all humans react in the same way to these allergens. For example, in a nonallergic person, mucus in the airway simply sweeps ragweed pollen to the throat, where it is swallowed or coughed out without ever triggering the immune system.
Related allergies and conditions
Conditions that are related to ragweed allergy include:
- Allergic rhinitis (hay fever). An inflammation of the mucous membranes that line the nose due to an allergic reaction to pollen, dust or other airborne substances. People with hay fever are at increased risk of developing other respiratory conditions because their allergy causes them to frequently breathe through their mouths. The nasal passages are lined with tiny hair–like structures called cilia that act like filters, preventing harmful particles from entering the body. When people breathe through their mouths, these filters are bypassed and particles can proceed directly to the lower respiratory system (e.g., lungs).
- Chronic rhinosinusitis. A chronic infection of the sinus cavities. The signs and symptoms of chronic rhinosinusitis include a yellow-green mucus discharge and chronic cough.
- Allergic rhinosinusitis. An allergy-triggered inflammation and infection of the mucous membranes lining the paranasal sinuses.
- Allergic bronchitis. An allergic inflammation in the lower airway of the respiratory system. It is a type of asthma, an inflammatory condition of the airways.
- Allergic conjunctivitis. An allergic inflammation of the tissues lining the inside of the eyelid.
Ragweed is a member of the plant family known as Compositae. It is one of the largest plant families and includes almost 20,000 different species including the daisy, artichoke, echinacea and dandelion. Plants are characterized according to family based on common features and similarities in structure. Families of plants will include a wide variety of plants that do not, on casual examination, look similar but share important characteristics that make them scientifically comparable. Plants that are members of the same family can create similar allergic reactions in an individual, a phenomenon known as cross-reactivity.
Oral allergy syndrome is a type of cross-reactivity in people highly sensitive to particular pollens. Ragweed allergy may induce oral allergy syndrome. During the seasons that ragweed pollinates, the patient may experience a rapid onset of itching in the mouth and throat after attempting to eat foods from the same plant family. The symptoms of this allergy will usually resolve quickly after the food is removed from the mouth.
Ragweed allergy sufferers may experience oral allergy syndrome to other members of the plant family, including the following plants:
- Honeydew melon
In addition, people with ragweed allergies should avoid using de-lousing products. The chemicals in these products may cause a cross-reaction in people with a ragweed allergy.
Allergic cross-reactions can range from mild to the severe systemic allergic reaction anaphylaxis, which can cause breathing difficulties and even death. It is important to know what plant family is associated with a person’s hay fever in order to ensure that proper precautions are taken to avoid all contact with ragweed allergens.
Symptoms and diagnosis
Ragweed allergy causes symptoms located in the head and throat. Symptoms include:
- Itchy, runny nose
- Nasal congestion
- Itchy and sore throat
- Red, itchy or watery eyes
Severe ragweed allergies may also result in sleep problems, fatigue, loss of concentration and poor performance at work or school.
Individuals who suspect a ragweed allergy can confirm the diagnosis by visiting an allergist/immunologist. A physician trying to diagnose ragweed allergy will take a complete medical history and perform a physical examination.
A skin test or blood test may be used to determine the allergen that is causing the patient’s symptoms. During skin testing for ragweed allergy, a doctor will prick or inject an extract of ragweed pollen into a patient’s skin and wait 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 certain skin conditions. In such cases, a blood test such as a radioallergosorbent test (RAST) may be used to measure whether or not an individual is allergic to ragweed. In this process, ragweed is introduced and a patient’s blood is checked for an increase of the IgE antibody, which indicates a potential allergy.
Treatment and prevention
The only effective way to prevent an allergic reaction to ragweed is to avoid any contact with the allergen (avoidance). However, this can be difficult during periods of ragweed pollination.
The amount of ragweed 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 ragweed pollen is to monitor the pollen count and modify behavior accordingly. Individuals with ragweed allergies should limit outdoor activities when the pollen count is high. Ragweed pollen levels tend to be highest in the morning, and on warm, dry, windy days.
Other steps people can take to cut down their exposure to ragweed pollen include:
- 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.
- Keep home and car windows closed.
- Shower frequently to wash ragweed pollen from hair and skin.
- Try to avoid mowing the lawn, weeding or raking leaves, as these activities stir up pollen spores. Wear a special allergen-proof mask when you do engage in these activities.
- Do not hang laundry outside. This allows ragweed pollen to collect on the fabric.
Ragweed allergy can also be treated with medication. Over-the-counter antihistamines can relieve sneezing, a runny nose and itchy, watery eyes. Nasal decongestants can reduce congestion. Patients with more severe ragweed allergies may require prescription medications, such as corticosteroid nasal sprays or mast cell stabilizers in the form of eye drops or nasal sprays.
Allergy shots (immunotherapy) may also be recommended. This treatment method helps prevent symptoms by increasing an individual’s tolerance to an allergen. Patients undergo a series of shots over a period of weeks, months or years with each shot containing more of the allergen to which the person is sensitive. 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 ragweed allergy.
Ongoing research regarding ragweed
There are medical research projects investigating the potential of developing a ragweed vaccine to treat ragweed allergy. Researchers at Johns Hopkins School of Medicine are working on a vaccine that contains only specific parts of ragweed allergens. This vaccine is administered one month before ragweed season with two to four injections over a two to three week period. Clinical trials of the vaccine are showing positive signs of treating ragweed allergy.
According to the Journal of Allergy and Clinical Immunology, a new form of immunotherapy is being tested for ragweed allergy. It consists of administering six injections of ragweed allergen over a six-week period. These immune shots are proving effective at treating the symptoms of ragweed allergy while eliminating the need for other allergy medications such as antihistamines and decongestants.
Questions for your doctor
Preparing questions in advance can help patients have more meaningful discussions with their physicians regarding their conditions. Patients may wish to ask their doctor the following questions about ragweed allergy:
- Do my symptoms suggest that I am allergic to ragweed?
- What methods will you use to determine if I am allergic to ragweed?
- Does this condition pose any danger to my overall health?
- What treatments are available to me?
- Will I experience symptoms year-round, or just at certain times of year?
- What steps can I take to avoid exposure to ragweed pollen?
- Where can I find the local pollen counts?
- Are my children more likely to develop ragweed allergy because I have the condition?
- Are there certain plants that I should not plant in my garden?
- What changes should I make in my diet in order to avoid cross-reaction?