Natalie Portman feels like she is ''constantly fighting against'' being judged based on her looks.

The 'Black Swan' actress - who began her career at the age of 13 - has opened up about the pressures women face to look a certain way and how ''tenuous'' it is that often a person's value is determined by their beauty.

Speaking in the September issue of Harper's Bazaar UK magazine, Natalie said: ''As a woman, you are constantly fighting against only being valued for your looks, because it becomes a very tenuous thing, to be defined by the gaze of others, the opinion of others.

''And beauty is, by definition, ephemeral, it's a thing that that you can't trap in time, it's a butterfly, it lives for a second.

''So to make a lifetime worthwhile and have meaning cannot rest on beauty...''

The 38-year-old star - who has Aleph, eight, and two-year-old Amalia with husband Benjamin Millepied - also admitted she feels women have been made to feel like they can't be ''angry''.

She explained: ''We've been socialised to believe that we're not feeling angry - we're feeling sad, we're feeling upset.

''And when I realised that, there was a sudden shift in my mind, and I thought, oh my God, all those times when I would burst into tears, I was actually angry!

''I just didn't know how to express it!''

Natalie will next star as astronaut Lucy Cola in 'Lucy in the Sky' - which has been produced by Reese Witherspoon - and she admitted she has been ''so inspired'' by the many women she has met following the launch of the Time's Up movement, which was launched in the wake of the Hollywood sex scandal in 2017, including 'Big Little Lies' star and producer Reese.

She said: ''I've been so inspired by the many women I've met through Time's Up - like Reese Witherspoon, America Ferrera and Kerry Washington - who are doing such impressive creative work, producing, acting, directing and taking such good care of their families. ''They are inspiring activists and also great friends. Whenever I think I have too much to handle, I see what they're doing and know I can do more.''

The September issue of Harper's Bazaar UK is on sale from Friday 2 August 2019.

Read online:

www.harpersbazaar.com/natalie.portman