Two of your social media apps could be collecting a lot of data on you — and you might not like what one of them is doing with it.
That's according to a recent study, published last month by mobile marketing company URL Genius, which found that YouTube and TikTok track users' personal data more than any other social media apps.
The study found that YouTube, which is owned by Google, mostly collects your personal data for its own purposes — like tracking your online search history, or even your location, to serve you relevant ads. But TikTok, which is owned by Chinese tech giant ByteDance, mostly allows third-party trackers to collect your data — and from there, it's hard to say what happens with it.
With third-party trackers, it's essentially impossible to know who's tracking your data or what information they're collecting, from which posts you interact with — and how long you spend on each one — to your physical location and any other personal information you share with the app.
As the study noted, third-party trackers can track your activity on other sites even after you leave the app.
To conduct the study, URL Genius used the Record App Activity feature from Apple's iOS to count how many different domains track a user's activity across 10 different social media apps — YouTube, TikTok, Twitter, Telegram, LinkedIn, Instagram, Facebook, Snapchat, Messenger and Whatsapp — over the course of one visit, before you even log into your account.
YouTube and TikTok topped the other apps with 14 network contacts apiece, significantly higher than the study's average number of six network contacts per app. Those numbers are all probably higher for users who are logged into accounts on those apps, the study noted.
Ten of YouTube's trackers were first-party network contacts, meaning the platform was tracking user activity for its own purposes. Four of the contacts were from third-party domains, meaning the social platform was allowing a handful of mystery outside parties to collect information and track user activity.
For TikTok, the results were even more mysterious: 13 of the 14 network contacts on the popular social media app were from third parties. The third-party tracking still happened even when users didn't opt into allowing tracking in each app's settings, according to the study.
"Consumers are currently unable to see what data is shared with third-party networks, or how their data will be used," the report's authors wrote.
TikTok tells CNBC Make It that the company recently conducted its own test of its app, using the same method as the study, which found that any network contacts went to only four third-party domains, all of which the company says are regularly used by other apps for functions such as network security and user certification, among others. Those third-party domains were Google, Apple, and Snap, as well as AppsFlyer, an advertising analytics company that measures the performance of marketing campaigns on the social media platform.
In October, Wired published a guide to how TikTok tracks user data, including your location, search history, IP address, the videos you watch and how long you spend watching them. According to that guide, TikTok can "infer" personal characteristics from your age range to your gender based on the other information it collects. Google and other sites do the same thing, a practice called "inferred demographics."
TikTok has been the subject of criticism in the past over how the company collects and uses data, especially from younger users, including claims that the company has transferred some private user data to Chinese servers.
In 2020, then-President Donald Trump looked to ban TikTok in the U.S. over concerns about the app's data security policies, before current President Joe Biden walked back those threats and ordered a review of potential security threats posed by foreign-owned apps.
YouTube did not immediately respond to CNBC Make It's request for comment.
UPDATE: This article has been updated with information provided by TikTok.