Although fake smiles often look very similar to genuine smiles, they are actually slightly different, because they are brought about by different muscles, which are controlled by different parts of the brain.

Fake smiles can be performed at will, because the brain signals that create them come from the conscious part of the brain and prompt the zygomaticus major muscles in the cheeks to contract. These are the muscles that pull the corners of the mouth outwards.

Genuine smiles, on the other hand, are generated by the unconscious brain, so are automatic.