The mother of Princess Beatrice, 30, and Princess Eugenie, 28, wrote in Hello! magazine: "We need to pay more attention than ever to what we're all being exposed to online. It's time to confront head on the fact that much of social media has become a sewer.
"I'm on Twitter and Instagram, and I'm grateful for the fact that they allow me to communicate directly with people who are interested, promote my charitable causes and let people read my own words rather than someone else's slant on them.
"But the truth is, a lot about these sites terrifies me. I rarely if ever go 'below the line' on social media or news websites and read people's comments."
Sarah Ferguson, or Fergie as she is more commonly known, was writing as part of Hello! magazine's new #HelloToKindness campaign, along with fellow celebrities such as the Beckhams, Liam Payne and Ronan Keating.
In the letter, the ex-wife of Prince Andrew addressed how women are often pitted against each other, drawing comparison between Kate and Meghan and herself and Princess Diana: 'Women, in particular, are constantly pitted against and compared with each other in a way that reminds me of how people tried to portray Diana and I all the time as rivals,
"Which is something neither of us ever really felt."