Anosmia

Anosmia

Loss of smell — anosmia (an-OHZ-me-uh) — can be partial or complete, although a complete loss of smell is fairly rare. Loss of smell can also be temporary or permanent, depending on the cause.
Although loss of smell can sometimes be a symptom of a serious condition, it isn't necessarily serious itself. Still, an intact sense of smell is necessary to fully taste foods. Loss of smell could cause you to lose interest in eating, which could lead to weight loss, malnutrition or even depression.

CAUSES

The common cold is the usual cause for a partial, temporary loss of smell; this will clear up on its own. Any obstruction in the nasal passages, such as polyps, also may cause at least a partial loss of smell. Aging, or even a brain tumor, may cause a complete and permanent loss of smell.
Problems with the inner lining of your nose
Anosmia can be caused by temporary or permanent irritation, or destruction of the mucous membranes lining the inside of your nose. This can be caused by:

• Acute sinusitis (sinus infection)
• Common cold
• Hay fever (allergic rhinitis)
• Influenza (flu)
• Nonallergic rhinitis (chronic congestion or sneezing not related to allergies)

These conditions are generally the most common causes of loss of smell.
Obstructions of your nasal passages
Anosmia can be caused by something physically blocking the flow of air through your nose. These obstructions can include:

• Bony deformity inside your nose
• Nasal polyps
• Tumors

Damage to your brain or nerves
Your olfactory system, which provides your sense of smell, consists of receptors in the mucous lining of your nose that send information through nerves into your brain. You can lose your sense of smell if any part of the olfactory pathway is damaged or destroyed. This can happen as a result of:

• Age
• Alzheimer's disease
• Brain aneurysm
• Brain surgery
• Brain tumor
• Chemical exposures to certain insecticides or solvents
• Diabetes
• Hormonal disturbance
• Huntington's disease
• Kallmann's syndrome (inability of testicles to produce sperm)
• Klinefelter syndrome (a condition in which males have an extra X chromosome in most of their cells)
• Korsakoff's psychosis (a brain disorder caused by the lack of thiamin)
• Malnutrition
• Medications (for example, some high blood pressure medications)
• Multiple sclerosis
• Multiple system atrophy (MSA) (a progressive disorder of the nervous system)
• Paget's disease of bone (a disease that affects your bones, sometimes facial ones)
• Parkinson's disease
• Pick's disease (a form of dementia)
• Radiation therapy
• Rhinoplasty
• Schizophrenia
• Sjogren's syndrome (an inflammatory disease that generally causes dry mouth and eyes)
• Traumatic brain injury
• Zinc deficiency

When to see a doctor
Loss of smell caused by colds, allergies or sinus infections usually clears up on its own after a few days. If this doesn't happen, consult your doctor so that he or she can rule out more-serious conditions.
Loss of smell can sometimes be treated, depending on the cause. Your doctor can give you an antibiotic to treat a bacterial infection, or remove obstructions that are blocking your nasal passage.
In other cases, anosmia can be permanent. In particular, if you're over age 60, you're more likely to lose your sense of smell.

Reference:http://www.mayoclinic.com/health/loss-of-smell/MY00408/DSECTION=when-to-see-a-doctor