A decline in the sense of smell is a symptom that warrants serious attention, as delayed treatment may lead to irreversible damage. One of the common causes of smell reduction is a cold, often presenting as nasal congestion that prevents odor molecules from reaching the olfactory region, located between the middle turbinate and the nasal septum. Once the nasal passage is cleared, odor molecules can enter the olfactory region, and the sense of smell naturally recovers. However, beyond nasal obstruction, certain viruses can also damage the nerve endings of the olfactory nerve. Acute flu viruses are usually self-limiting, and the sense of smell will typically return in a short period. But other viruses, such as herpes viruses that invade the nervous system, can cause more severe damage to the nerve endings of the olfactory nerve and may even lead to viral olfactory neuritis. This type of olfactory damage may take a long time to recover and, in some cases, may not recover at all.

For example, the COVID-19 virus often causes loss of smell, with recovery times varying from person to person. Some cases may experience prolonged olfactory impairment, and although research on the long-term effects of COVID-related smell loss is still ongoing, it has been confirmed that the virus can cause significant olfactory dysfunction. In addition to COVID-19, many other viruses can also lead to similar olfactory disorders.

Apart from viral infections, damage to the olfactory center in the brain can also cause a loss of smell. In cases where patients become sensitive to specific odors or experience a worsening olfactory disorder over time, it is important to investigate whether there is a tumor or other mass lesion affecting the olfactory center. In hospitals, magnetic resonance imaging (MRI) is typically used to check the condition of the olfactory center. Early treatment of nerve damage is crucial, and it is generally recommended to begin within one week to maximize the chances of recovery.

Additionally, exposure to harmful substances is another potential cause of olfactory damage, especially in certain occupations. For example, workers in the chemical industry who are exposed to harmful chemicals over long periods may suffer damage to their olfactory nerves. Moreover, poor-quality construction materials used in renovations may lead to olfactory allergies or nerve damage. Although this is not very common, it is still occasionally observed in clinical practice.

When diagnosing olfactory disorders, it is important not only to identify the underlying cause but also to conduct qualitative and quantitative smell tests. Simple subjective smell tests involve exposing the patient to various odors to assess their sense of smell. Recently, objective smell tests have also been introduced in clinical practice. These tests involve specific stimuli to conduct a localization examination of the olfactory nerve to determine the segment and severity of the olfactory disorder, predict the likelihood of recovery, and assess whether the damage is located in the central nervous system or at a specific level of neurons or other structures.