Too many.

No one knows the answer. Why not? Read this: http://www.snopes.com/science/smile.asp An excerpt: "Everyone has heard it a different way, and everyone passes along the version they've heard as rock-solid certainty, presenting same as an indisputable fact of science. Here is a quick sampling of some of ways this saying has been framed, as gleaned from a variety of news articles on any number of topics, including sports, music, and health: One deep-fried-Zen adage advises: "It takes 13 muscles to smile and 33 to frown. Why overwork?" (Washington Post, 5 Dec. 1982) "You know the old adage that it only takes 10 muscles to smile but it takes 100 to frown," she said. (New York Times, 19 April 1987) According to doctors we use only four muscles to smile, but when we frown we use 64 muscles ? 16 times more. (The Hindu, 11 March 2000) It's easier to smile than to frown. A smile uses 17 muscles, a frown, 43. (Milwaukee Journal Sentinel, 24 Feb. 1997) Right there, you commit to selling to all employees ? at cost, not a nickel of markup ? company T-shirts that say, "It only takes one muscle to smile and 37 muscles to frown." (St. Louis Post-Dispatch, 24 April 1995) Don't they know it is said you use 35 muscles to frown and four to smile? Why tire yourself? ([Queensland] Sunday Mail, 18 Aug. 1991) Sonny Smith, Auburn's basketball coach, on his dour counterpart at the University of Alabama: "It takes 15 muscles to smile and 65 muscles to frown. This leads me to believe Wimp Sanderson is suffering from muscle fatigue." (New York Times, 16 Dec. 1986)" "The saying's age is not its only mystery; there's no real agreement as to how many muscles have to be worked in the face to produce a smile or a frown. And,given that even what constitutes a smile is up for grabs (some avow the muscles around the eyes get involved; others discount that and look only to those necessary to lift the corners of the mouth), it's possible this is one of those questions for which there will never be a definitive answer. Yet whatever medical science ultimately decides about how many angels are dancing on the head of this particular pin, we would say the resultant numbers would be immaterial because it's the homily's underlying message that matters, not the raw facts of it. The maxim has been handed from generation to generation because of its enduring value as implied advice rather than its being an authoritative tally of a parts list. More simply, the lore lives because of what it says about people, not their anatomy, so to get lost in the bean-counting aspect of it would be at the expense of losing sight of its far more important component." So, there's your answer - there's no definitive number.

From: http://www.suite101.com/article.cfm/our_beautiful_bodies/96786 We humans have many superficial muscles in head and face. They help us in expressing our feelings. They are attached to various parts of the facial skin. Loosely they are called as "muscles of facial expression". There is an epicranial musculo-fibrous sheet in our scalp extending from forehead right up to the top of skull and backside of the skull. This muscle helps in raising eyebrows to show horror, surprise or doubt. Entire scalp can be moved by alternately moving frontalis and occipitalis i.e. the front and back parts of this muscle. Australopithecus robustus, was a human ancestor living a million and half years ago. They had a cranial crest running in midline of the dome of skull. On either side of this crest were muscles which probably moved the scalp much more extensively and forcefully than we are capable of. Around the external ear are three small muscles that allow some people to twitch their pinna a little. But they are not important in showing or changing the human facial expression. A dog or cat can prick the ears and orient them to source of sound with these ear muscles. Around our eyelid are the orbicularis oculi muscles in the form of a ring. These muscles help us in voluntary and involuntary blinking, and control tear duct. Around the nose there are several small muscles, like procerus, nasalis, depressor septi. With the help of these muscles we can frown, flare or compress the nostrils. The mouth is surrounded by muscles like - elevators, retractors and evertors of upper and lower lips and a circular ring of muscles orbicularis oris. Orbicularis oris causes closing of the mouth, and rounding and protrusion of the lips. The buccinators, (from buccina, a trumpet) which are at the side of face between the two jaws help in compressing the cheeks. Some of the facial muscles are just broad thin sheets like the - Quadratus labii superioris. This muscle helps in raising the upper lip upward. Most of the muscles of facial expression are around the eyes, nose and mouth i.e. our bodies "windows to the world". These muscles are subcutaneous that is just beneath the skin and unlike other skeletal muscles some of them are not attached to the bones. The facial muscles can pull the corners of the mouth up or down, show grin, displeasure, puff, grimace etc. They also help in eating food and in chewing it. If the facial muscles are healthy and well toned the face looks younger and brighter.

Twice as many as it does to smile. My doctor told me this. I smile a lot.

According to my health stuff (I am teaching health), it takes 40 muscles to frown!