Loss of the ability to smell is called anosmia, a sensation that almost everyone experiences when suffering from a cold, allergies, or a sinus infection. But occasionally, anosmia can be a long-term or permanent disorder in which a person either is born without or loses the sense of smell as a result of head trauma, medication side effects, a brain tumor, or enlarged structures in the nasal cavities. People with no sense of smell react to the world in a different way: They have a limited sense of food flavor, can’t detect smoke or other dangerous odors, and can’t appreciate the aromas that other people take for granted.

One cause of anosmia is Kallmann syndrome, a rare inherited disorder that affects mostly men. People with Kallmann syndrome are born with little or no sense of smell, fail to go through puberty, and are often sterile and have small genitalia. This stems from a deficiency of gonadotropin-releasing hormone (GnRH) being produced in the hypothalamus; GnRH is a chemical that plays a role in sexual maturity and helps regulate the olfactory bulbs, which give us our sense of smell. The condition can also be associated with color blindness and other vision problems, although scientists are not sure why.

Kallmann syndrome can be treated, in part, by restoring the deficient hormones through infusion pumps or injections. This can induce fertility, but only temporarily. The disorder can also have a psychologically isolating effect on its victims.

In people who don’t have Kallmann syndrome, some loss of the sense of smell occurs normally with aging. Some people may be born anosmic for one particular odor, such as fish or sweat, a condition called specific anosmia. Loss of smell may also be caused by Alzheimer’s disease, endocrine system disorders, lead poisoning, nutritional disorders, radiation therapy, or medications such as amphetamines, estrogen, or nasal decongestants.

ADDITIONAL FACTS

  1. People with anosmia can’t perform certain basic tasks, like smelling milk to tell if it has gone bad, and must take special precautions against such dangers.
  2. Doctors can diagnose anosmia by using scratch-and-sniff odor tests or by testing with familiar odors such as coffee, lemon, grape, vanilla, and cinnamon.
  3. Many people who are born with anosmia report having lied as children and pretended that they could smell things that other people could—mimicking others’ facial expressions, for example—so that they’d appear normal.