People are often more worried about how they look than they like to admit.
But this is doesn't necessarily mean they are 'vain'. Vanity means having too much pride in how you look.
Most animals who glance in a mirror think that they are face to face with another member of their species.
But the great apes - chimps, gorillas and orang-utans - are can recognise themselves in the mirror.
They use mirrors to groom themselves, pick food out of their teeth and pull faces - more or less the same as humans!