Marketers will no longer be able to resort to "harmful gender stereotypes" to sell products or services under a new ban that has come into force today.
The new rule in the Advertising Codes states that advertisements "must not include gender stereotypes that are likely to cause harm, or serious or widespread offence".
It applies to broadcast and non-broadcast media, including online and social media.
Under the ban, an ad that "seeks to emphasise the contrast between a boy's stereotypical personality (e.g. daring) with a girl's stereotypical personality (e.g. caring) needs to be handled with care".
The ban is being implemented after a review by the Advertising Standards Authority (ASA) concluded that a "tougher line needs to be taken on ads that feature stereotypical gender roles or characteristics which, through their content and context, may be potentially harmful to people".
"This includes ads that mock people for not conforming to gender stereotypes," the review said.
Examples cited in the report included portrayals of women as the sole person with responsibility to clean up a mess in the home, a man "trying and failing to undertake simple parental or household tasks", and ads that suggest "an activity is inappropriate for a girl because it is stereotypically associated with boys or vice versa".
It said that such adverts had the potential to cause harm "by inviting assumptions about adults and children that might negatively restrict how they see themselves and how others see them".
This in turn, the report said, might lead to "unequal gender outcomes" in the public and private sphere, and "limit choices" that people make in life.
A consultation on whether to ban harmful gender stereotypes in adverts was supported by a majority of respondents.
The ASA said: "The evidence does not show that the use of gender stereotypes is always problematic and the new rule does not seek to ban gender stereotypes outright, but to identify specific harms that should be prevented."
A review of the ban will be carried out after 12 months to assess its effectiveness.
Guy Parker, Chief Executive of the Advertising Standards Authority, said: "Our evidence shows how harmful gender stereotypes in ads can contribute to inequality in society, with costs for all of us.
"Put simply, we found that some portrayals in ads can, over time, play a part in limiting people's potential. It's in the interests of women and men, our economy and society that advertisers steer clear of these outdated portrayals, and we're pleased with how the industry has already begun to respond."