Facebook will soon begin rolling out its long-promised ‘clear history’ feature – and has warned advertisers that it may have an impact on targeting options.

The feature, first announced last May, will enable Facebook users to see and manage all the information that has been shared with Facebook about them from other websites and apps. It will include a list of the apps and websites a user visits that use Facebook’s business tools, such as Facebook pixel, SDK, and API.

Though Facebook suggests the transparency and control will be good for businesses because improves the way people “feel about ads and the businesses they interact with online”, it could also put a dent in the scale of their advertising efforts.

“When someone disconnects their off-Facebook activity, we wont use the data they clear for targeting,” said the company in a blog post. “This means that targeting options powered by Facebooks business tools, like the Facebook pixel, cant be used to reach someone with ads. This includes Custom Audiences built from visitors to websites or apps. Businesses should keep this in mind when developing strategies for these kinds of campaigns in the second half of the year and beyond.”

The hit to targeting, however, won’t hurt measurement and analytics, which “have been carefully designed to protect people’s identity”. And, overall, Facebook believes the feature will have a “positive, long-term effect”.

“We welcome Facebooks announcement on the ‘clear history’ tool that will allow users to delete data that the social network gathers from websites and apps outside of Facebook, and no longer use that data for advertising,” said Yuval Ben-Itzhak, Socialbakers CEO.

“Marketers should look at a GDPR-safe approach where content is created and targeted based on interests of users on each digital channel”