The olfactory nerve is a cranial nerve. It exclusively contains nerves related to the sense of smell. It is one of the only cranial nerve that the body can repair if it is damaged.
In diagnosis, a failure to smell out of both nostrils can indicate damage to the olfactory nerve, although this is not specific to olfactory nerve damage. Lesions on the nerve from trauma or infection can lead to partial loss of smell. It is normal for the sense of smell to become less acute with age.