Overview Cacosmia is a disorder of the sense of smell. It’s a type of parosmia. It occurs when there’s a problem somewhere along the pathway of smell. When this happens, a person is unable to recognize smells or interpret the odors of different substances. Around 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 though they can smell something offensive, when in fact no such substance is present. When the sense of smell, or olfactory system, is not working correctly, a person can perceive even pleasant odors to be foul smelling. With cacosmia, the smell is often described as similar to feces, or a burning, rotten, or chemical odor. The condition can lead to distress among those who experience it, as it causes a persistent feeling of smelling something unpleasant.

What are the symptoms? Sensing a persistent foul smell is the main symptom of cacosmia. Since smell and taste are closely linked, the condition can also affect your ability to eat. It may make it difficult to identify the actual smell of different foods, or it may cause foods that you usually enjoy to suddenly taste foul. 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 it makes them sick.

What are the causes? Problems in any one of three main areas of the smell pathway will cause issues with smell. These three areas are: the olfactory sensory neurons within the nose

the smell signal

the olfactory bulbs underneath the front of the brain, one above each nasal cavity Olfactory sensory neurons (OSNs) line the inside of your nose. They are receptor cells found in the lining of the mucous membrane in the nose that receive smells and relay the sensation to the olfactory areas in the brain. When OSNs become damaged or inflamed, they can send a distorted signal to the brain. In other cases, the smell signal can become blocked. This blockage prevents the smell signal from reaching the nose or the brain. In cases of brain injury or disease, the olfactory bulbs can become damaged, leading to problems with smell. 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 differentiating smells. Smoking Smokers often experience cacosmia and other smell disorders. This is believed 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 The smoke from harmful chemicals and acids can also damage the OSN. This damage leads to a distorted sense of smell. Medication and cancer treatments Some medications can lead to an impaired sense of smell, particularly long-term use of antibiotics. Radiation therapy used to treat cancer of the head and neck can also injure the sensory cells. Sinus tumors Cancer of the sinuses and other tumors and growths can affect smell. Symptoms can include one side of the nose being blocked, a wide range of changes in smell, worsening nasal congestion, and pain. Neurological diseases Diseases such as Alzheimer’s disease, Parkinson’s disease, schizophrenia, and epilepsy can all affect the area of the brain that is responsible for processing smells.

Treatment options There is no cure for cacosmia, but the symptoms can improve over time, especially if the cause is treatable, such as a respiratory infection or smoking. Researchers are currently looking at 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 looking at how gene therapy and stem cell therapy may be useful. People who are particularly affected by the disorder can opt to have their olfactory bulbs surgically removed. This will completely alleviate the symptoms, but it will also leave the person with no sense of smell whatsoever. Surgery may also be useful in cases where growths in the nose or sinuses are blocking the path between the smell and the olfactory neurons.

Potential complications and associated conditions Our sense of smell has an important role in memory, enjoyment of the natural world, and enjoyment of food. When the sense of smell pathway is disrupted, it can affect individuals on a variety of physical, emotional, and psychological levels.