This letter originally appeared in Dr. Hoffman's column on allHealth.com. |
Q: I have asthma very bad, and every time I get sick I can't smell for a long period of time. Sometimes this happens when I'm not sick. Can you tell me why I can't smell?
A: Smell and taste are chemical senses: your nose and tongue are able to detect very dilute concentrations of chemicals, and are able to differentiate among hundreds of different chemicals. The specialized cells, or "receptors," which do this detective work are (in the case of smell) located at the very roof of the nasal cavity. Put your fingertip on the bridge of your nose, right between your eyes. Imagine an area about one inch deep to your fingertip. THAT’S where all of the action is.
You can only smell chemicals that are in the gas phase (airborne). Yes, you can smell liquids, but that’s only because a small portion of the liquid is entering the gas phase at any given instant. When we inhale through our noses, a portion of the inhaled air circulates to the roof of the nose. Any chemicals present in this air will dissolve into the mucus that coats the receptors for smell. The dissolved (mucus phase) chemicals trigger the appropriate receptors, and your brain interprets this information appropriately.
Anything which blocks this chain of events will result in anosmia (loss of the sense of smell). If your nose is too congested, no air will circulate to the roof of the nasal cavity. If your nose is excessively dry and there is an inadequate mucus layer covering the receptors, then the gas phase chemicals will have difficulty entering the mucus phase. Many drugs can affect the degree of nasal congestion and/or the consistency of nasal mucus; it is possible that one or more of the drugs you take for asthma are causing anosmia in this fashion. Many drugs act directly upon the receptors to cause anosmia. Your doctor may have to sit down with a list of your medications and the PDR (the Physician’s Desk Reference, which has detailed information on all prescription drugs) to figure this one out.
This assumes that your anosmia is a consequence of your asthma treatment. There is another possibility, however. Folks with chronic infection of the nose and sinuses (rhinosinusitis) who also have asthma will often notice that the two problems seem interrelated. Nasal mucus containing bacteria (living and dead), pus and a variety of inflammatory chemicals can make its way down to the lungs and provoke an attack of asthma. An acute exacerbation of chronic rhinosinusitis will also be associated with nasal inflammation, which causes decreased air flow through the nasal cavity, which in turn causes anosmia. Thus, one problem (recurrent exacerbations of chronic rhinosinusitis) could be causing both your asthma and your anosmia.
Discuss this with your doctor. With appropriate questioning and examination, he should be able to differentiate among these possibilities. Your treatment may involve changing the drugs used in the treatment of your asthma; alternatively, you may need treatment for rhinosinusitis. This could involve antibiotics, other drugs to reduce nasal inflammation or to treat nasal allergies, and (if all else fails) surgery to improve sinus drainage.