Girls as young as seven believe women are judged on beauty not brains, a survey has revealed.
More than a third (35%) of seven to 10 year-old girls agreed that women were rated more on their appearance than their abilities - and 36% said they were made to feel their looks were their most important attribute, the Girlguiding's Girls' Attitudes Survey 2016 found.
Campaigners said the findings showed the need to combat the "objectification and harassment" which are "ruining girls' lives".
The survey also revealed low levels of body confidence among girls.
Almost two fifths (38%) of seven to 10 year-olds said they felt they were not pretty enough, while 23% said they felt they needed to be "perfect" and 15% said they felt embarrassed or ashamed by the way they looked.
Across seven to 21 year-olds, there has been a five-year decline in levels of body confidence, the survey found.
In 2011, almost three-quarters of girls (73%) said they were happy with the way they looked, compared to just 61% this year.
Sam Smethers, chief executive of the Fawcett Society, said women and girls were "persistently judged on what they look like" and suffered "significantly higher" rates of depressions and mental illness.
"This is serious. As a society we need to face up to the fact that objectification and harassment is ruining girls' lives and we are letting it happen," she said.
Dr Carole Easton, chief executive of the Young Women's Trust, said the survey revealed the presence of "gender inequality" from a young age.
"If we are serious about ensuring that everyone has an equal opportunity to get on in life, then much more must be done to ensure a level playing field - starting from childhood and into young adulthood, not least by challenging gender stereotypes," she said.
The Girlguiding association is challenging the public to praise young women using the hashtags #YouAreAmazing and #GirlsAttitudes on social media, to help improve body confidence issues.
Becky Hewitt, Girlguiding director, said: "Girls have told us to stop judging them on how they look.
"Every day in guiding, girls inspire us with their bravery, sense of adventure and their kindness.
"We are calling on everyone to show girls that they are valued for who they are - not what they look like."