The following conditions that may lead to loss of smell:
1. Increased nasal mucus production caused by a number of ailments such as colds, influenza, hayfever or sinusitis.
2. Chemicals, a wide range of industrial chemicals including heavy metals, inorganic and organic compounds, acids and pollutants.
3. Diseases of the hormonal system such as diabetes and of the nervous system such as Alzheimer's disease, multiple sclerosis, migraine, brain tumors, brain lesions and epilepsy.
4. General diseases such as bronchial asthma and cystic fibrosis.
5. Drugs that include stimulants (such as amphetamines and cocaine), depressants (such as morphine) and other drugs including the vasoconstrictors in nasal sprays.
6. Ongoing process in the nose and/or sinuses such as nasal allergies, rhinitis (inflammation in the nose).
7. Respiratory virus infection. A viral infection can lead to sinusitis in susceptible patients.
8. Medications such as some antibiotics, high blood pressure medications and chemotherapy.
9. Trauma, including blows to the head or injuries to the nose.
10. Injury of the specialized nerve tissue at the top of the nose from previous viral upper respiratory infections.