The often-repeated advice that smiling is to be preferred to frowning because 'it takes more muscles to frown than to smile' is false.
A genuine (also known as 'zygomatic') smile uses the following muscles:
• Zygomaticus major
• Zygomaticus minor
• Orbicularis oculi
• Levator labii superioris
• Levator anguli oris
There are two of each of these, one on each side of the face, giving a grand total of 12 muscles.
To frown, you need the orbicularis oculi, platysma, depressor anguli oris and corrugator supercilii, of which there is again one on each side of the face, plus the procerus, orbicularis oris and mentalis which are all single muscles, giving a grand total of 11.
For most people, however, the smiling muscles are better exercised than the frowning ones, so using them may take less energy.
The insincere smile is the most energy-efficient, and can be accomplished with the use of only the two risorius muscles.
The word for someone who never smiles is 'agelast' or 'agelastic'.