This dictionary says
blow: 2 a : to create a current of moving air by breathing
[no object]
She blew on her fingers to warm them.
He was blowing on his soup to cool it off.
[+ object]
She blew air into the balloon.
But other dictionary says
blow: 3 AIR FROM YOUR MOUTH [intransitive, transitive always +
adverb/preposition] to send air out from your mouthblow (something) into/onto/out etc
She blew onto her coffee to cool it down.
He blew the smoke right in my face.
So, we say:
She blew on or in his face?
Best Answer
Blowing air at a persons face is a very rare action.
If you "blow in his face" it suggests an annoying action. We could also say "She threw a cup of water in his face". If you blow smoke at someone it is nearly always annoying: nobody wants to breath your smoke.
On the other hand "blow on his face" could be to warm it, or as a lover's game. It is a gentle action. You need to be quite close to someone and the situations where this would happen are rare. On the other hand, it is quite common to blow on your own hands.