Dogs lick people for more than one reason.
Affection can be part of it.
So can attention, taste, habit, and learned behavior.
Licking starts early
Puppies experience licking from their mother.
Dogs also use licking in social interactions with other dogs.
The behavior therefore begins long before a dog decides your face is available.
Licking can be social
A dog may lick a familiar person during greeting or calm interaction.
That can be part of bonding.
The behavior may function as an affiliative social signal.
Humans taste interesting
Skin contains salt, oils, food residue, lotions, and other scents.
Dogs investigate the world with both nose and mouth.
Sometimes the explanation is not emotionally profound.
You are simply flavored.
Licking can get attention
If licking makes a person laugh, pet the dog, speak, or look down, the behavior has been rewarded.
Dogs learn quickly what works.
A lick can become a reliable attention button.
Can licking be self-soothing?
Yes.
Some dogs lick themselves, objects, or people more when excited or stressed.
Repetitive licking can help regulate arousal.
Excessive licking may also point to anxiety, skin irritation, pain, or another problem.
Is a lick the same as a tail wag?
No single dog behavior has one universal translation.
Dogs wag their tails for several emotional states.
Licking is the same way.
Context matters.
A dog lick can mean affection.
It can also mean you taste interesting and the behavior has worked before.
And that’s the short explanation.
Related explanations: Why do dogs wag their tails?, Why do dogs tilt their heads?, and Why do dogs sniff each other’s rear ends?