Courtesy of Jonathan Bernstein.
Ragweed
In the Midwest, August 15th is an important day for allergy sufferers. It is the beginning (plus or minus) of the ragweed season which continues until the first frost around mid-October. It is estimated that 10-20% of the US population has ragweed allergies.
What are ragweeds? Ragweeds are flowering plants in the genus Ambrosia which is part of the aster family, Asteraceae. Ragweed is found in tropical and subtropical parts of the Americas, especially North America. The major allergen in ragweed is Amb a 1 which is about 38 kilodaltons and 10-30 microns in diameter. In other words, these are very small, microscopic proteins that can easily float in the air and blow all around when it is dry and windy. To be allergic to ragweed, a person must demonstrate specific immunoglobulin E or “sensitization” to the specific allergen. This can be confirmed by a skin prick skin test or a blood test. Having a positive test however, doesn’t mean you are necessarily allergic. The positive test should correlate with exposure to the allergen. In other words, if a person has a negative ragweed allergen test but goes outdoors when ragweed levels are high and experiences sneezing, runny nose, nasal stuffiness, eye watering and itching among other potential symptoms, they would be called “allergic” to ragweed. Why is this important to distinguish from just a positive test? Any test has a positive and negative predictive value as well as a sensitivity and specificity. So it is possible that someone can be sensitized to an allergen but not “allergic.” There are many potential reasons for this, but we will save this discussion for another time. Meanwhile, its ragweed season, and you know its coming because every year you are sneezing your head off, having a runny nose, severe itchiness of the eyes, nose, ears and sometimes soft palate especially when you eat melons and bananas. What can you do to prevent this misery from happening. First, you should confirm you have a true ragweed allergy. Although typically patients with allergies have a positive family history on either parent’s side, this is not always clear as their parents may never have seen an allergist or ENT to confirm the diagnosis. Once the allergy is confirmed, it is important to have options for treatment. Avoidance is possible by keeping windows closed and running the A/C at home and work. This is not always possible if you work outdoors, are an outdoor enthusiast or don’t have A/C. For mild symptoms, non-sedating second generation antihistamines which are mostly over the counter will help sneezing, itching and runny nose but don’t help with congestion. For more moderate to severe symptoms there are several topical nasal corticosteroids and H1-antihistmaine nasal sprays over the counter that if used correctly can prevent and control symptoms. Finally, a more definitive treatment to induce ragweed tolerance is either to undergo allergen immunotherapy with a series of injections to ragweed and other relevant sensitizing allergens over a 3-5 year time period or using sublingual therapy (SLIT) which is now commercially available for grass, ragweed and dust mite in the US. Some physician offer OIT drops that are touted to be effective but there are few if any well-designed clinical trials demonstrating their effectiveness. Nonetheless, patients often choose SLIT or OIT as they are more convenient, can be done at home and are associated with a lower risk of allergic reactions.
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