Many times apps will recognize something called an IDFA (iPhone’s Identifier for Advertisers) along with any history associated with the number, allowing the companies to trade info on you. When an app connects with your IDFA, it won’t be long until ads are hitting your newsfeed.
Fortunately, you can restrain advertisers from accessing this number:
On IOS, find Settings > Privacy > Advertising >turn on Limit Ad Tracking.
While you are at it, go ahead and reset the advertising identifier.
Android’s system isn’t too different:
Find Settings > Google > Ads > Opt out of Ads Personalization.
Read our full article on how to limit Facebook’s use of your data here.