Why do people say Mwah when kissing each others cheek ?

They don't when they're actually kissing, only when they fake it, usually because they don't want to smudge a woman's make-up.

Since you still pout your lips to pretend, it's the most obvious sound to make.

Mwah ;-)

@ the answer above : totally agree, nothing as embarrassing as to be left standing there kissing empty air, when your friend has already drawn back. Just stop at two, if they need more, just grin and say sorry lol.

It's supposed to represent lips smacking in a kissing motion. The people concerned don't want to kiss each other, but they want to go through a social formality and therefore approach the cheek of the other person and make a kissing noise rather than actually osculate.

Hey! Join the club! It's so insincere and is usually associated with a near miss. If you don't want to embrace someone, then don't. End of story!

Living in central continental Europe, my biggest problem is remembering how many times you 'embrace'. Some countries do it twice, some three times and others four times, but none of them ever say 'mwah.

Mwah is the onomatopoeic sound for a kiss. So I reckon people do it to exagerate the kiss, or when they just put their cheek, to pretend that they are actually kissing you.

No - idea - it is a substitute for actually kissing their cheeks

They are pretentious idiots,enough said.