TikTok is under formal investigation over concerns it has failed to protect children from harmful content, the UK’s online regulator, Ofcom, has announced.

The social media platform’s approach to checking the ages of users has sparked “particular concerns” at the watchdog, almost a year after measures to protect children from the worst of online content came into effect under the Online Safety Act.

Ofcom said TikTok is using a method of inferring children’s ages that may have failed to correctly identify “a significant proportion of children”, putting them at risk of exposure to harmful content.

The regulator said it had not reached any conclusions, but that compliance failures could be punished with fines of up to £18m or 10% of qualifying worldwide revenue, whichever is greater. Harmful content includes posts about disordered eating, self-harm, suicide and pornography. Ofcom can also apply to have sites blocked or restricted in the UK in the most serious cases.

Ofcom said: “This investigation will seek to establish whether there are reasonable grounds to believe that TikTok has failed, or is failing, to comply with its legal obligations … including by using age assurance that is highly effective at correctly determining whether or not a particular user is a child.”

TikTok says that it requires users to enter a date of birth when they create an account. It says “we also use technology that looks at information, often called ‘signals’, to check for indicators that someone may not meet our minimum age requirement.”

The investigation comes as the UK government prepares to launch a social media ban for under-16s early next year, which will increase scrutiny of the methods tech companies use for verifying users ages.

Ofcom said it also had “serious doubts” about other platforms using techniques that infer users’ ages. It said that “in some cases, tech companies may be failing to correctly detect significant numbers of children on their platforms, meaning children risk being exposed to harmful content”.

It said “those which use age inference models to comply with their child protection duties should switch to other methods listed in our guidance as highly effective without delay”.

For example, Ofcom’s research found that about one in 10 teenagers aged between 15 and 17 were still using the three most-used dating apps in December 2025, despite age checks being in place.

TikTok is the third most used site or app by 8- to 14-year-olds, after YouTube and WhatsApp, according to Ofcom’s studies, with children spending an average of eight hours 45 minutes a week on video-sharing platforms, including TikTok, YouTube, Twitch and DailyMotion.

In a statement, it said: “We strictly enforce age-appropriate experiences through expert-informed platform rules and ​advanced age inference technologies, in line with ​major ⁠industry peers. We are confident that we meet ⁠our ​Online Safety Act obligations and ​will work with Ofcom to demonstrate this.”

It also says it does not allow content that promotes disordered eating or shows risky weight management behaviours.

Meanwhile, Ofcom has also warned that children are too easily finding links to pornography sites with no age checks by using search engines. It has found that one in three results returned on the first page of Google Search and 54% on Microsoft-owned Bing sent users to such check-free sites.

The regulator said about a quarter of the UK’s most popular pornography services in the UK had no checks in place. Since 25 July last year, all sites and apps in the UK which allow pornography have been required under the Online Safety Act to have age checks in place to protect children from accessing harmful content.

Ofcom said the two search engines will now be working with the regulator to tackle the discoverability of pornography sites which still do not have age checks.

Microsoft declined to comment. Google has been approached for comment.