Why is it that only sometimes I have dimples?

[Anonymous]

When I smile sometimes dimples show up and sometimes they don't. It's not consistent and I don't know why. What causes them?

[Afro-dite9]

Ohh this happens to me a lot as well. I don't know what causes it, it's weird. Maybe it depends in the muscles you use when you smile.

[Anonymous]

The muscles in the face contract differently at times