Hmm.. sure many of you have seen T-shirts or read online trivia claiming to be facts.. on how it takes about 30-40 muscles to frown, and 17 to smile?... ever sat and wondered if its true?

Consider this... there are about 52 muscles involved in the head... and only about 36 involved with facial expressions.. (numbers vary due different classifications)... so yeah.. suddenly frowning seems to take up the muscles of your entire face eh? LOL
Well, quoting from the plastic surgeon interview on Straightdope.com...

Muscles involved in a "zygomatic" (i.e., genuine) smile:

Zygomaticus major and minor. These muscles pull up the corners of the mouth. They're bilateral (one set on either side of the face). Total number of muscles: 4.

Orbicularis oculi. One of these muscles encircles each eye and causes crinkling. Total: 2.

Levator labii superioris. Pulls up corner of lip and nose. Bilateral. Total: 2.

Levator anguli oris. Also helps elevate angle of mouth. Bilateral. Total: 2.

Risorius. Pulls corner of mouth to the side. Bilateral. Total: 2.

Grand total for smiling: 12.


Muscles involved in a frown:

Orbicularis oculi (again). Total: 2.

Platysma. Pulls down lips and wrinkles skin of lower face. Bilateral (though joined at midline). Total: 2.

Corrugator supercilii (bilateral) and procerus (unilateral). Furrow brow. Total: 3.

Orbicularis oris. Encircles mouth; purses lips. Unilateral. Total: 1.

Mentalis. Depresses lower lip. Unilateral. Total: 1.

Depressor anguli oris. Pulls corner of mouth down. Bilateral. Total: 2.

Grand total for frowning: 11.

So yeah, there is a slight difference.. but its likely that we are used to smiling that the muscles are conditioned and thus smiling seems easier. Interestingly, seeing a genuine smile usually causes viewer to smile back, similar to how hearing or seeing a yawn causes one to yawn too.

However, that said, it is even easier to fake a smile, taking up only 2-4 muscles, mainly for the arching and pulling back of the lips.. without the contraction or twinkling of the eyes.. but can we really tell the difference?
If you wanna test out how well you would do recognizing fake and genuine smiles... head over here for a short online quiz