This is the cranial nerve involved in the process of olfaction - the sense of smell.
It is not a routine part of the neurological examination to test the function of the olfactory nerve - its function is assessed subjectively by asking the patient if they can smell things, and whether their sense of smell has altered recently; many patients will notice a loss of taste first - this should trigger the same line of investigation. Note that this line of enquiry will only elicit bilateral anosmia, and that if there is any suspicion of a lesion then each nostril ought to be formally tested.
Testing can be grossly performed by pressing a nostril closed, exposing the other to cut orange peel or soap, determining whether the patient can smell this with eyes closed, and then repeating on the other side.
Last reviewed 01/2018