Why do dogs lick other dogs’ eyes or mouths?

If you have more than one dog, like me, you might have noticed your dog licking the eyes or mouth of your other dog. Do you wonder why they do it? Seems a bit gross, but there must be a reason for it. So I did some digging (pardon the pun) and this is what I found

Licking another dogs eyes

There can be several reasons for this.

• Dogs might lick each other when they are trying to appease the other or show signs of submission. 
• It could be a case of mutual grooming.  Some dogs have more ocular discharge and/or tear production than others.  There can be many reason for this, but one thing is common to all of the causes and that is the fact that their little faces need to be cleaned.  If not, this discharge can lead to infection of the skin surrounding the eyes.  

Licking another dogs mouth

• Playtime – licking each other’s mouth is often a sign they are ready to play.
• Saying I’m sorry – dogs can get frustrated with each other, especially if one is more high-energy. The offending pooch can say she’s sorry with a gentle face lick. She usually comes in from below and licks the other dog’s mouth, and she might raise a paw slightly, says the ASPCA. When the other dogs licks back, all is forgiven.
• Submission – Licking is often a sign of submission. A dog lower down the chain might greet one higher up the chain by licking her on the mouth. She also might roll over onto her back to express her submissiveness. Keep an eye on dogs when one is submissively licking
• Hunger – it is a way of puppies showing an older dog they are hungry.The big dog isn’t likely to feed the puppy — that’s your job — but the puppy doesn’t necessarily know that. Instinctively, she thinks it’s the adult dog’s job to find food and bring it back for her to eat.

So when your dog’s  do this behaviour you have some insight why.