|MadSci Network: Medicine|
Allergies that are strictly seasonal tend to be caused by airborn pollens or spores. Spring allergies are usually caused by tree pollens, and fall allergies are usually caused by weed pollens or mold spores. Of course, for any individual, other specific allergens may be the major cause of their symptoms. Either skin testing or RAST testing (using a blood sample) together with definition of additional features of the history can be used to pinpoint the most likely allergen(s) causing the symptoms. This kind of evaluation is best handled by a board-certified allergist.
Variation of the intensity of symptoms during the day can be due to many causes that we understand, or to causes we don't understand. Firstly, the level of exposure clearly makes a difference. For example, some of the trees release their pollen more at specific times of the day. With the night-time symptoms that you describe, it could be possible that your exposure is higher at night. Do you sleep with the windows open? Does the furnace or airconditioner come on in the middle of the night, leading to a puff of dusty pollen that has collected in the ducts during the preceding portion of the day? Are you perhaps also sensitive to house dust mite? This is an antigen that accumulates in high quantities in pillows and mattresses, and to which you may get a high exposure while you sleep. From the point of view of normal physiology, sleep results in the downregulation of a number of physiological pathways. Firstly, when you go to sleep, the mucociliary blanket (a thin layer of mucus that is secreted by cells that line the airway from the nose down to the small branches of the airway in the lungs, and which is moved from the airway to the throat by the action of cilia on the airway cells, and then swallowed) also goes partially to sleep. The mucus is moved to the throat more slowly and with less efficiency. The purpose of this mucociliary blanket is to trap inhaled viruses, bacteria, pollens, and other particles and to facilitate their removal before they can damage the airway lining cells. So, at night, inhaled allergens are cleared less effectively, and remain in contact with the airway cells for longer periods of time, causing more intense symptoms. In the eye, during sleep, less tears are produced, so again pollens and other antigens are cleared less effectively. Additionally, there are circadian rhythms in immune function that may affect how strongly one reacts to the challenge of an antigen.
As far as what to do, certainly keep the windows closed during your allergy season. Change furnace filters once a month whether they appear to need it or not. Encase your box spring, mattress, and pillow with dustproof covers (available from any department store/Target). And take an antihistamine before going to bed. There are many inexpensive over the counter antihistamines available. You may prefer one of the non-sedating, longer acting antihistamine which are available only by prescription. Additionally, saline eyedrops may help wash allergens out of your eyes. Other treatment might also be suggested by an allergist based on the results of allergy testing. This could include allergy shots, which have the potential to prevent the allergic reaction in the first place.
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