Allergy Update

November 28, 2010

Amber Luong, MD, PhD
Associate Professor


This past spring represented one of the worst allergy seasons in Houston. The unusually long cold season delayed some trees from blooming and consequently led to an usually high peak in the number of trees blooming at one time. Oak is one of those trees whose pollen is highly allergenic. For the last 4 years, the highest pollen counts ranged from 2062 to 2669 grains per cubic meter. This year, the oak pollen counts topped 6,000 grains per cubic meter.

The allergy season starts with tree pollen in January and extends in Houston to September because of our local areas short winter season. The common tree pollen producers in Houston include Cedar, Elm, Pine, Oak, Ash, Hackberry, Pecan and Cedar Elm.  The next season after tree pollen is grass. For Houston, grass counts typically start to rise in March and begin to taper in July. The local common allergy-causing grass pollens include Timothy, Bermuda, Bahia, Orchard, Sweet vernal, Red top and some blue grass. The most common St. Augustine grass in Houston luckily is not highly allergenic. The final allergy season of the year is ragweed which starts in mid-August and extends until the cool weather sets in.

With the high humidity, Houstonians are exposed not only to the typical pollens and ragweed allergy seasons, but also deal with relatively higher fungal exposure than other parts of the country.  Molds can be highly allergic and have been shown to trigger sinus and asthma disease. The molds common to Houston include Cladosporium, Ascomycetes, Alternaria, Basidiomycetes and various Dermatiaceous or pigmented fungal species. The mold counts are related to the moisture in the environment with higher counts associated with increased rain fall. So, this summer’s rainstorms caused total mold counts in Houston to skyrocket to just under 10,000. For comparison, the maximum mold count in June last year was only 7698.

Although this year was somewhat unusual, the overall prevalence of allergic rhinitis has been trending higher worldwide over the last several decades, and more so in developing countries. Interestingly, allergies are more common in the developed world such as the United States.  In the United States, it is estimated that 1 in 5 suffer from allergic rhinitis. There remains no clear explanation for the upward trend, but a popular theory is the hygiene theory. Basically, this theory purports that if exposure to bacteria is limited during early childhood, this can alter the immune system such that it becomes more reactive to typically innocuous agents such as pollen or dust mite later in life. The recent trend of anti-bacterial agents being added to everything from wipes to hand soap all have significantly reduced everyday bacterial exposure.

Allergic rhinitis is defined by symptoms consisting of running nose, sneezing, nasal congestion and watery eyes.  More significant than these symptoms, allergic rhinitis is often associated with impairment in quality of life. Many people suffering from allergic rhinitis often complain of fatigue, difficulty thinking and overall difficulty performing at work or school during exacerbation of allergy symptoms.  In addition, allergic rhinitis is commonly associated with other respiratory ailments including sinus infections and asthma. So control of allergic rhinitis symptoms can often improve or prevent this other co-morbid ailments.

Although generally difficult to accomplish, avoidance of allergens is typically recommended for the initial management of allergy symptoms. When the allergen is the favorite cat or dust mite that resides in everyone’s homes, avoidance is often not practical.  In addition, there are currently no studies that have demonstrated clear benefit with only avoidance measures. Given the prevalence of allergic rhinitis, it is not surprising that most people seeking help with symptoms opt for medical therapy. Anti-histamine are readily available without a prescription. Anti-histamines block the histamine that is released from inflammatory cells during an allergy response from its receptor. The newer generation anti-histamines are characterized by their non-drowsy benefit. These include cetirizine (Zyrtec), loratadine (Claritin), fexofenadine (Allegra), and desloratadine (Clarinex). Unlike the first generation antihistamines such as diphenhydramine (Benadryl), the second generation formulations do not cross the blood-brain barrier. Cetirizine and loratadine are available over-the-counter while fexofenadine and desloratadine both require a prescription. The antihistamines can be very effective for rhinorrhea, sneezing and itchy eyes/ears/nose and throat, but less effective in relieving nasal congestion. Upon taking the medication, relief of symptoms is generally noted within 1 to 3 hours. And the medication is generally dosed daily.

To relieve the nasal congestion, intranasal steroids are often recommended concurrently with an antihistamine. Intranasal steroids allow topical delivery of steroids to the nasal mucosa. The effects of the steroids are rather complex and still not fully elucidated. But ultimately, the intranasal steroids suppress the inflammatory response. Again, several formulations are available, but unlike the antihistamines, all require a prescription. And unlike the onset of action for the antihistamines, the full response to the intranasal steroids can take several weeks to develop. Long term therapy at the recommended doses appears to be safe; however, it is impossible to dismiss the possibility that long term intranasal steroid use may have systemic effects.  Published studies evaluating the effects of topical steroids on the systemic regulation of endogenous steroids have found minimal effects.

Other medical therapy options in addition to oral antihistamine and intranasal steroids include topical antihistamines, leukotriene antagonist, local cromones, oral and intranasal decongestants, oral steroids and topical anticholinergics. The data on these medications are less clear in terms of benefits in management of allergic rhinitis.

And finally, if medical therapy has failed, immunotherapy has proven to be effective in altering the immune system such that it is less response to targeted allergens. These allergy shots require a commitment by the patient and treating physician as shots are generally given on a regular basis for 3 to 5 years. New studies on sublingual immunotherapy may provide in the near future the long term advantages of immunotherapy while being able to administer the treatment at home. Studies are actively ongoing in this area of allergic rhinitis therapy.