Pervasive online abuse and harassment pressure women and girls into censoring themselves on social media and fuel gender-based discrimination and violence, rights groups said on Monday.
About one in four women in Britain, the United States and six other countries said in a survey they had experienced online abuse or harassment.
More than 40 percent said the online abuse made them fear for their physical safety and more than half reported trouble sleeping, loss of self-esteem and panic attacks after the incidents, according to rights group Amnesty International.
About a third stopped expressing their opinions online or withdrew from public conversations as a result, Amnesty said.
"It's no secret that misogyny and abuse are thriving on social media platforms, but this poll shows just how damaging the consequences of online abuse are," said Amnesty researcher Azmina Dhrodia. "This is not something that goes away when you log off."
Online harassment starts at a young age and may be more common for girls and teenagers than adults, according to U.K.-based child rights group Plan International.
Nearly half of girls aged 11-18 in the U.K. said they had experienced abuse or harassment on social media, Plan found in a survey earlier this year.
Like women, most of the girls said they stopped sharing opinions or otherwise changed their online behavior out of fear, according to Plan.
"Very young girls are learning that they need to take responsibility for harassment and abuse," Kerry Smith of Plan told the Thomson Reuters Foundation. "What they are saying is that they are holding themselves back."
Parents, teachers and police often respond to online abuse by taking away girls' phones or telling them to go offline, which teaches victims that they are responsible for the problem, Smith said.
Online harassment, including crude comments on pictures or sexual references, teaches boys that it is okay to treat girls as sexual objects and to exercise power over them, which can lead to physical abuse and rape, she added.
Social media attacks are so common for female politicians that they deter women from running for office around the world, advocates and female lawmakers have said.
Companies and governments need to step up to make the internet a safe space for girls and women, campaigners said.
"Social media companies have a responsibility... to ensure that women using their platforms are able to do so freely and without fear," said Amnesty's Dhrodia.