Most cat owners I know admit to kissing their cat. It seems perfectly normal among cat lovers, but non "cat" people (not to mention my mother) seem baulk at the idea. But the question is, is it safe to kiss your cat?
If you have a healthy immune system and your cat is free of disease and parasites then giving him the odd peck is probably not going to cause you any harm (although there is a small chance). However, it is not advised that you kiss a cat who is sick, nor do I recommend kissing cats on the lips. Many diseases can be passed on from cats to humans (zoonotic). Cats and humans can become infected with common bacteria such as Pasteurella, staphylococcus, e-coli and salmonella. All of which are highly contagious. Ringworm is a common fungal infection that easily spread from cats to humans and vice versa via direct contact. While not serious, it is a pain to treat and once you have it, you can pass it on to other people or animals.
There is research to suggest that just like humans, cats contain certain bacteria in their mouths which cause gum disease. Not only can gum disease lead to loss of teeth, but it has a greater impact on the organs. A peck on the head is just as enjoyable and carries less risk of transmission of disease. Also, cats have scent glands on their cheeks and lips which secrete feel good "pheromones" when they rub on objects (such as the sofa, doors, YOU), and a kiss from their human companion may be seen by your cat a similar demonstration of affection and ownership as the cat would display to you.
Some theorise that children living with pets have lower rates of allergies. Much debate surrounds children growing up in increasingly sterile environments, with the use of modern hand sanitisers and disinfectants. A child's immune system needs to be "challenged" in order to develop. It has been said that living with pets from the first year of life can decrease the rate of allergies in children as their immune system is exposed to various bacteria and viruses from your pet that they wouldn't ordinarily be exposed to. These stimulate the immune system, helping it to develop in a healthy manner instead of turning on itself and developing allergies. Now in order for your child to be exposed, he or she doesn't need to kiss your pet, and I am certainly not advocating that children should do so, but it is interesting to note that pets may actually help to strengthen immunity and/or reduce allergies.
Caution should always be used when getting your face close to a cat, especially one you don't know or a cat who is agitated. I will only ever kiss my own cats and only when they are calm and relaxed. Make sure your cat is regularly treated for parasites such as worms and fleas and is up to date on his vaccinations.
So, if you want to give your cat a quick peck then as long as you have a healthy immune system and your cat is disease free then there really is no reason why not. Immunocompromised people (such as those with HIV, undergoing cancer treatment), and young children should not kiss cats.