For as long as I can remember I haven't been able to smell. I can tell when there is a distinct CHANGE in odor, though I cannot identify what it is. I went to a doctor who said I would grow out of it. Well, now that I'm 19 I would like to know what exactly my problem is, and if there is anything that can be done. Smelling is such a big part of your everyday life that this really worries me.

A.

Olfaction is the ability to smell. What you describe is, I suspect, diminished olfaction, or hyposmia. Complete loss of olfaction is known as anosmia. Hyposmia and anosmia are serious problems. At a minimum, they diminish the quality of life by impairing the sense of taste (which depends heavily on the sense of smell) and lessening the richness of the environment. Hyposmia and anosmia can also result in sickness (through ingestion of spoiled or contaminated food) and injury (for example, because of impaired ability to smell smoke in a burning building).

There is a lengthy list of possible causes:

1. Head trauma. Even minor head trauma can result in olfactory impairment. The olfactory nerves are very delicate. They travel from the roof of the nasal cavity, across the base of the skull, to the base of the brain. If you can imagine spaghetti poking down through the holes of a colander, you will have a good idea of the relevant anatomy. Now imagine that the spaghetti within the colander has glommed together into a giant, sticky pasta-ball (the brain). If you shake the colander roughly, you might shear off the bits of spaghetti that are poking through the colander holes. This is (we think) how head trauma causes olfactory loss. Surgery to the nasal cavities or skull base is another type of trauma that may lead to anosmia.
   
2. Nasal inflammation. Allergies, sinusitis and other inflammatory conditions of the sinuses and nose can cause swelling of the tissues that line the nasal cavity. If swelling is so great that air is unable to reach the region near the top of the nasal cavity, where the olfactory nerve receptors are located, there will be no sense of smell.
   
3. Obstruction of the nasal cavities. Just as inflammatory disease can prevent air flow to the smell receptors, abnormal nasal anatomy can do the same. Severe deviation of the nasal septum, which divides the nasal cavity into two parts, can contribute to anosmia, particularly when inflammatory disease is also present.
   
4. Nasal tumors. These are uncommon, but they must be considered whenever a person develops anosmia of relatively recent onset -- typically within weeks to months, not years. (This is very unlikely for you, given your youth and the fact that you have had this problem for so long.)
   
5. Colds and flu. Some people have permanent olfactory loss following a viral respiratory tract infection. The exact cause is mysterious. This is an uncommon problem, and it tends to be relatively more common in older individuals.
   
6. Medications. The list of medications that may cause anosmia is lengthy. Exactly how the drugs impair olfaction are unknown.
   
7. Toxic chemicals. Many different toxins can impair the sense of smell.
   
8. Congenital and hereditary anosmia. In rare cases, people are born without the sense of smell.
   

What should you do? See an ear, nose and throat doctor (ENT). An ENT has the training and knowledge to obtain a thorough medical history from you and to perform a careful examination. You will need nasal endoscopy (inspection of your nasal cavities with a flexible fiberoptic telescope) and you may also need further radiologic studies, such as a sinus and nasal CT scan or an MRI of the brain.

Is all this really necessary? Some of the conditions described above are correctable. If you don't investigate the problem, you will never know.