January Jones feels sexier without makeup on.

The 'Mad Man' star has confessed she prefers to let her natural beauty shine through and enjoys going barefaced when she isn't dressed up on set.

She said: ''I feel sexy and vulnerable when I have no makeup on.''

The 37-year-old actress added she isn't as confident now as she was in her childhood and hopes to encourage young girls to love themselves regardless of what they look like.

She said: ''I was at my most confident as a kid.

''It actually wasn't until I got into high school and started to get quote-unquote pretty that my confidence started to disappear.

''So I want to give the message that girls can be proud and self-assured no matter what funky haircut they have.''

The blonde beauty - who is known for sporting retro inspired looks as housewife Betty Draper on the hit AMC drama opposite Jon Hamm - also hinted at a surprising end to the series when the final season airs on April 5.

She told Violet Grey's The Violet Files: ''I was surprised, but the show has always surprised me. Each episode is so good and sort of ties up things - not in a perfect bow, obviously - but I think the audience will be happy.''