Thank you for your enquiry. Your smell nerves (olfactory nerves) have small fibres that pass from your brain through the bone that separates your brain from the nasal cavity (known as skull base) to the top part of your nasal cavity. For any smell or odorant to be detected, it has to reach the top part of the nasal cavity.
There are two main types of loss of sense of smell. The first type is known as "conductive loss", which is due to a physical blockage in your nose that prevents the smell/odorant from reaching the smell nerve fibres on the top part of the nasal cavity. This may be due to mucous and swelling in the nose from cold, flu, nasal allergies, nasal polyps and rarely nasal tumours. When the physical blockage is reduced, e.g. when there is less mucous or swelling in the nose when your cold/flu or nasal allergies is better, you regain your sense of smell. This is because the odorant can now reach the smell nerve branches and get detected. Hence, conductive losses are usually reversible.
The second type of loss of sense of smell is known as "sensorineural loss". This is due to inflammation, infection or physical damage of the smell nerve fibres. Common causes include viral infections (e.g. during a cold/flu), sinusitis, head trauma and rarely brain or nasal tumours. Unfortunately sensorineural losses are usually irreversible, especially if the inflammation or infection has caused a permanent damage to the smell nerve fibres.
Fever from a cold/flu can cause both conductive and/or sensorineural loss of sense of smell. It is quite likely that your "loss of taste" (i.e. your food/drinks taste bland or is "tasteless") is due to reduced or loss of sense of smell. This results in a loss of appreciation of food flavours. True loss of taste e.g. inability to detect sweetness, sourness, saltiness or bitterness is rare.
If your sense of smell is not better a few weeks after your fever, you should see an ENT Specialist for an assessment.
Hope this helps and all the best!
