Cats do not sniff each other’s noses. They touch each other’s noses in a friendly greeting. To reiterate, when cats who are friendly towards each other meet and touch noses they are not sniffing each other’s noses. They are simple touching or near-touching. There does not necessarily have to be contact. How do I know? Note: If the cats are not greeting and sniff noses (I have not seen this – rare?) it is to smell the breath. My cat will smell my breath if I have eaten something spicy for instance.
Me and my cat…we touch noses as a greeting! Of course I have to pick him up so that we are face to face. As soon as we are face to face he wants to do a nose touch greeting. Sometimes he’ll touch noses three times or more. Other times he will do it once and not actually touch my nose.
But, he never sniffs my nose. I am watching him and he is obviously very close to me so I’d notice if he was sniffing me. He isn’t. This is confirmed by an authoritative book, The Welfare of Cats edited by Irene Rochlitz (a great book by the way).
“As mentioned previously, cats are not asocial; within a colony they may form close relationships with other cats. They show a variety of affiliate behaviours, including touching noses, allogrooming, allorubbing, playing and resting together.”
So the question in the title is incorrectly formulated. The question that I have is, “Why is touching noses a friendly greeting for domestic and feral cats?” And it applies between species as I do it with my cat.
What comes to mind is the traditional Māori greeting. It is called the Hongi and is done by pressing noses and foreheads together. It is the equivalent of the handshake.
Cats touching noses is very similar. What underpins both is the formal and gentle contact which takes place which helps bonding and to create friendship. It is interesting that humans and cats share a very similar type of greeting.
P.S. Cats also like to extend their foreleg to use their paw to touch their human or animal companion when resting. I have seen it happen between cat and dog and cat and human (me). It is based on the same principles: it is pleasant for the cat and the recipient and it enhances bonding and strengthens the friendship.