There are two types of smiles, according to Finnish researchers Dr. Jari Hietanen of the University of Tampere and Dr. Veikko Surakka of the Institute of Biomedicine at the University of Helsinki. One smile category is known to experts as social smiles. These are prompted merely by a sense of obligation and involve only the muscles of the cheeks. Genuine smiles, on the other hand, express real feelings of pleasure and activate not only the muscles of the cheeks but also the muscles around the eyes.
A recent study from Finland suggests that genuine smiles are contagious. By detecting and recording minute muscle movements, researchers found that the subjects of their experiment were induced to smile merely by looking at a photograph of someone with a genuine smile. This reaction was not observed when the subjects looked at pictures of people displaying social smiles.