It is difficult to say how many muscles it takes to smile or frown because all people make different expressions when smiling and frowning. What might be a thoughtful look for one person is another person's frown. The number of facial muscles present also varies between individuals.
If the smile and frown are stripped down to basics, a minimum number of muscles can be defined. A smile where only the corners of the lip and the upper lip are raised uses five muscle pairs; two of them raise the upper lip and three of them raise the corners. A frown where only the corners of the mouth and the lower lip go down uses three muscle pairs. One pair drops the lower lip, and two pairs lower the corners. The minimum number of muscle pairs for a smile is five, and for a frown it is three.