The idea behind the poster is critiquing the problem when people, especially women, spend too much time on managing their exterior beauty: shopping for cosmetics products, losing weight, plastic surgery, makeups. Always trying too hard to be "perfect", but what defines "perfect" or "beautiful"? They'll never be satisfied with their look, the endless journey to cosmetic and makeups, sometimes even lead to depression. The thing is, the real true beauty is always there under all the cosmetic products, it is the true self.
The poster uses a metaphor, defines makeup as a mask, it's something you put on to conceal your inner beauty. Notice how the expression on the mask is sad, not confident.
I wanted to encourage people to look into their heart and see that inner beauty lies within themselves, it is so beautiful that no makeup is able to achieved. Be confident and be real, because every one of you is worth it!