Thursday, June 30, 2011

Seasonal Allergies

MassGeneral Hospital for Children allergist, Rajashri Shuba Iyengar, MD, MPH, shares the "101" on seasonal allergies

Seasonal allergies are an abnormal reaction to an ordinarily harmless substance, in this case pollen. This condition is also called "hay fever." Pollen is inhaled into the body of an allergic person and causes activation of the immune system. The pollen, or allergen, is seen by the cells of the immune system as harmful. The white blood cells, which normally defend against infection, produce IgE antibodies. These antibodies attach to specialized cells known as mast cells, prompting the release of active chemicals. The chemicals, like histamine, then cause itching and congestion. Therefore, a seasonal allergy sufferer has episodes of itchy/watery eyes, runny nose, sneezing, and itchy throat. In some people, these allergies also can trigger asthma.

A person suffering from allergies can be sensitive to just a few or many different types of pollens from trees, grasses, weeds as well as mold spores. The time of year that an allergic person develops symptoms depends on many factors, including the geographic region they live in as well as the months that the specific pollen that triggers the allergy is released.

The propensity to develop allergies is genetically determined. Therefore, people with seasonal allergies should work with their allergist to find out what they are allergic to and how to keep their allergies under good control. Allergy treatment plans involve "detection and protection." This includes using specialized testing methods to determine what specific allergens a person is sensitive to. It also involves using proper avoidance techniques and medications.


The effect of rain on seasonal allergies is complex and frequently unpredictable. Rain hydrates the soil and promotes growth of plants and vegetation. Therefore, we sometimes observe higher pollen counts after a heavy rainfall. However, rain can also weigh down pollens and decrease counts. As a result, pollens carried by the air, like tree pollens, are usually weighed down during heavy rain.

There are also associations between thunderstorm activity and asthma deaths as well as emergency room visits. Some scientists speculate that cold air in the storm sweeps up particles such as pollen, and concentrates them in a narrow band of air close to the ground. Also, specific molds in the air may play an important role in sensitive people.

Global Warming

It is believed that global warming, which includes both warmer temperatures and higher ambient carbon dioxide levels, speeds up the flowering of plants. This can result in earlier plant blooming, causing pollen seasons to start earlier. Climate change has also been linked to longer pollen seasons, greater pollen exposure, and increased allergic disease. This means that a seasonal allergy sufferer can expect to have more severe symptoms over a longer period of time due to the effects of global warming.

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