Cacosmia: what is it, and how does it affect the perception of odors?

Overview of Cacosmia

Cacosmia is a disorder of the sense of smell. It is a type of parosmia. It occurs when there is a problem somewhere along the olfactory pathway. When this happens, a person is unable to recognize odors or interpret the smells of different substances. About 14 million people in the United States are believed to have a disorder related to the sense of smell.

People with cacosmia often feel as if they can smell something offensive, when in fact no such substance is present. When the sense of smell, or the olfactory system, is not functioning properly, a person may perceive even pleasant smells to have a bad odor. With cacosmia, the odor is often described as similar to feces, or a burning, putrid, or chemical odor.

The condition can lead to distress among those who experience it, as it causes a persistent sensation of smelling something unpleasant.


What are the symptoms?

The detection of a persistent foul odor is the main symptom of cacosmia. Since smell and taste are closely linked, the disease can also affect your ability to eat. It can make it difficult to identify the actual smell of different foods, or it can make foods you usually enjoy suddenly taste bad. It can become extremely difficult to eat a sufficient amount when every bite tastes offensive. Some people even find the smell and taste of food to be so bad that it makes them sick.

What are the causes?

Problems in any of the three main areas of the odor pathway will cause problems with smell. These three areas are:

  • the olfactory sensory neurons inside the nose
  • the odor signal
  • the olfactory bulbs under the front of the brain, one on top of each nasal cavity
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olfactory sensory neurons (OSNs) line the inside of the nose. They are receptor cells found in the lining of the mucous membrane of the nose that receive odors and transmit the sensation to the olfactory areas in the brain. When OSN become damaged or inflamed, they can send a distorted signal to the brain. In other cases, the odor signal may be blocked. This blockage prevents the odor signal from reaching the nose or the brain. In cases of brain injury or disease, the olfactory bulbs may become damaged, leading to problems with odor.

There are many different reasons for cacosmia.

Upper respiratory tract infection

Upper respiratory tract infections such as bronchitis, sinusitis, rhinitis, or sore throat can cause damage to the OSNs leading to cacosmia.

Head injury

Some head injuries can damage the olfactory bulbs in the brain, which are responsible for odor differentiation.


Smokers often experience cacosmia and other smell disorders. This is thought to be due to direct injury to the OSN. The damage can be short-term or long-term. The longer and more frequently these cells are exposed to the toxins in cigarettes, the worse the damage over time appears to be.

chemical smoke

Smoke from harmful chemicals and acids can also damage the OSN. This damage leads to an altered sense of smell.

Drug treatments and cancer

Some medications can lead to an erroneous sense of smell, particularly long-term use of antibiotics. Radiation therapy to treat head and neck cancer can also damage sensory cells.

Breast tumors

Breast cancer and other tumors and growths can affect odor. Symptoms may include one side of the nose being blocked, a wide range of changes in odor, worsening nasal congestion, and pain.

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neurological diseases

Diseases such as Alzheimer’s disease, Parkinson’s disease, schizophrenia, and epilepsy can affect the area of the brain that is responsible for odor processing.

Treatment options

There is no cure for cacosmia, but symptoms may improve over time, especially if the cause is treatable, such as a respiratory infection or smoking. Researchers are currently looking for new options that may help improve many types of smell disorders. Scientists are investigating ways to combat the inflammation that leads to the damage, along with examining how stem cell therapy and gene therapy may be helpful.

People who are particularly affected by the disorder may choose to have their olfactory bulbs surgically removed. This will alleviate the symptoms completely, but will also leave the person with no sense of smell at all.

Surgery may also be helpful in cases where growths in the nose or sinuses are blocking the pathway between the odor and the olfactory neurons.


Potential complications and associated conditions

Our sense of smell plays an important role in memory, enjoyment of the natural world, and enjoyment of food. When the sense of smell pathway is altered, it can affect people on a variety of physical, emotional, and psychological levels.


The chances of recovery from cacosmia are excellent when the cause of the condition is reversible. For example, if cacosmia has been caused by nasal inflammation, the symptoms usually subside after the inflammation is treated. However, if the cause of the problem is more serious, recovery may not be possible.

People may find that the symptoms of cacosmia subside after some time has passed. When this is not the case and a person has been living with the disease for some time, they may want to talk to their doctor about the possibility of surgery. Future surgical options may include stimulating the repair and growth of olfactory nerve cells through the use of stem cells and skin grafts.

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