Societal standards state we must wear clothing when we're out in public, and this standard of decency has made some feel self conscious about their naked bodies, or at least when they're naked around other people.
This nudity-related self-consciousness causes people to make certain facial expressions whenever they're naked around an unfamiliar person, expressions that sometimes include a nervous grin.
Photographer Dylan Hamm reveals people's facial expressions before and after undressing in his series "Naked Faces", a side-by-side portrait series that challenges viewers to guess which one's the nudie pic.
See "Naked Faces" Reveals How Someone's Expression Changes When Becoming Undressed here