A person with a normal sense of smell (normosmia) can distinguish between 10,000 smells. The sense of smell stimulates salivary glands, which is why the sense of taste is connected to the sense of smell. People with smelling disorders usually have some loss of taste also.

A dysfunctional sense of smell is generally not life-threatening, but it can be dangerous. Without a sense of smell, a person might eat spoiled food, might not be able to detect a gas leak or smell if something is burning. Loss of smell and the resulting loss of taste could also lead to depression.

Sometimes the loss of the sense of smell, anosmia, is temporary, like with a cold or flu. On the other hand, a head injury could cause permanent anosmia. A head injury could also produce dysosmia, the distorted sense of smell that causes a person to hallucinate a foul odor.

Smelling disorders can be defined as follows:

Anosmia - this the loss of the sense of smell. This is the most common smelling disorder and it can be temporary or permanent.

Dysosmia - this is a distorted sense of smell that causes a person to hallucinate unpleasant odors. It is usually caused by medical or mental conditions.

Hyperosmia - this is an increased sensitivity to smell.

Hyposmia - this is the diminished sense of smell. This is usually a temporary condition caused by the flu.

Presbyosmia - this is loss of smell that occurs when a person ages.

Smelling disorders can be caused by many things. Some of the most common causes are nasal polyps, viral upper respiratory infection, atrophic rhinitis (wasting away of the mucus membrane), hypertrophic rhinitis (thickening of the mucous membrane), smoking cigarettes, a crooked nose or a deviated septum, destruction of the olfactory bulbs, tracts, or central connections (caused by head trauma, infections or sinus surgery), head injury, prolonged use of medications such as antihistamines and decongestants, drugs like amphetamines, estrogen, naphazoline, phenothiazines, and resperine, the aging process, a tumor behind the nose or in the membranes surrounding the brain, lead poisoning, exposure to insecticides or other chemicals, radiation therapy, and nervous disorders.

There are many different treatments for smelling disorders. These treatments range from lifestyle changes to surgery. Treating mental disorders can sometimes affect the sense of smell, but in some cases the sense of smell can't bereinstated. Anosmia associated with aging is not treatable.

Some common treatments for smelling disorders are saline sprays, quitting smoking, over-the-counter antihistamine such as Actifed, avoiding allergens, antibiotics for infections, prescribed steroids such as Prednisone, surgical treatment, removal of nasal polyps and benign tumors, septoplasty to straighten the nasal passage, rhinoplasty to straighten the structure of the nose, and sinus surgery to open sinus drainage channels.

Not all causes of smelling disorders are preventable. People with a smelling disorder obviously should not smoke and should ask those around them not to smoke. People who have smelling disorders related to allergies should try to to avoid what they're allergic to. Since head trauma injuries can lead to smelling disorders, people should wear protective helmets when bicycling or participating in sports like football or hockey.