Sniffing Out the Cause of Olfactory Illusions

My patient, in whom allergic rhinitis has been diagnosed, has been receiving weekly allergy shots since June 2003 for allergies to dust, grass, mountain cedar trees, and ragweed. She has benefited greatly from these shots. However, she complains that she sometimes smells "cigarette smoke" for periods of 2 to 3 days--even though she is never exposed to it. What might be the cause of this?

— MD

When the olfactory membrane is inflamed or is undergoing changes, distortions in smelling often occur. Smelling smoke-like odors is not uncommon. It is presumed that this phenomenon reflects abnormal stimulation of the olfactory receptor cells. Odorant quality is coded by a combination of receptor cell activations. It is possible that an allergen used in the shots induces a reaction within the olfactory epithelium, which, in turn, produces the smoke-like dysosmia.

— Richard L. Doty, MD