What are the causes?

There are several medical conditions and medications associated with a loss of smell. The possible causes include: a viral infection affecting the upper respiratory tract , such as a cold persistent (chronic) sinusitis , with or without nasal polyps a nose abnormality , such as a crooked nose or a nasal septum (wall dividing the nostrils) that isn't straight hay fever (rhinitis) that causes severe inflammation of the nasal passages certain medication , including antibiotics such as metronidazole recreational drug use such as cocaine or amphetamines diabetes long-term alcohol misuse an underactive thyroid Cushing's syndrome (high levels of the hormone cortisol in the blood) exposure to a chemical that burns the inside of the nose a head injury a brain tumour radiotherapy to the head and neck epilepsy Parkinson's disease Alzheimer's disease stroke liver or kidney disease vitamin B12 deficiency schizophrenia granulomatosis with polyangiitis an uncommon disorder of the blood vessels sarcoidosis a rare disease that causes body cells to form into clumps In general, anosmia is usually caused by either a problem with odours getting to the top of the nose (because of swelling or a blockage in the nose) or a problem with nerve signals from the nose to the brain. However, in around 20% of cases, the cause can't be found. This is known as idiopathic anosmia. Congenital anosmia An estimated 6,000 people in the UK are born without a sense of smell because of a genetic condition or faulty gene. This is known as congenital anosmia. It can occur alone (isolated congenital anosmia) or it can be a symptom of another genetic condition, such as Kallmann syndrome or Klinefelter syndrome .