TikTok, known in China as Douyin (Chinese: 抖音; pinyin: Dǒuyīn), is a short-form video hosting service owned by Chinese company ByteDance. TikTok and Douyin have almost the same user interface but no access to each other's content. Their servers are each based in the market where the respective app is available. The two products are similar, but features are not identical. Douyin includes an in-video search feature that can search by people's faces for more videos of them and other features such as buying, booking hotels and making geo-tagged reviews.

User privacy concerns
Privacy concerns have also been brought up regarding the app. In its privacy policy, TikTok lists that it collects usage information, IP addresses, a user's mobile carrier, unique device identifiers, keystroke patterns, and location data, among other data. Web developers Talal Haj Bakry and Tommy Mysk said that allowing videos and other content being shared by the app's users through HTTP puts the users' data privacy at risk.

In January 2020, Check Point Research discovered a security flaw in TikTok which could have allowed hackers access to user accounts using SMS. In February, Reddit CEO Steve Huffman criticised the app, calling it "spyware," and stating "I look at that app as so fundamentally parasitic, that it's always listening, the fingerprinting technology they use is truly terrifying, and I could not bring myself to install an app like that on my phone." Responding to Huffman's comments, TikTok stated, "These are baseless accusations made without a shred of evidence." Wells Fargo banned the app from its devices due to privacy and security concerns.

In August 2020, The Wall Street Journal reported that TikTok tracked Android user data, including MAC addresses and IMEIs, with a tactic in violation of Google's policies. The report sparked calls in the U.S. Senate for the Federal Trade Commission (FTC) to launch an investigation.

In June 2021, TikTok updated its privacy policy to include collection of biometric data, including "faceprints and voiceprints." Some experts reacted by calling the terms of collection and data use "vague" and "highly problematic." The same month, CNBC reported that former employees had stated that "the boundaries between TikTok and ByteDance were so blurry as to be almost non-existent" and that "ByteDance employees are able to access U.S. user data" on TikTok."

Addiction concerns

There are concerns that some users may find it hard to stop using TikTok. In April 2018, an addiction-reduction feature was added to Douyin. This encouraged users to take a break every 90 minutes. Later in 2018, the feature was rolled out to the TikTok app. TikTok uses some top influencers such as Gabe Erwin, Alan Chikin Chow, James Henry, and Cosette Rinab to encourage viewers to stop using the app and take a break.

Many were also concerned with the app affecting users' attention spans due to the short form nature of the content. This is a concern as many of TikTok's audience are younger children, whose brains are still developing.[180] TikTok executives & representatives have noted and made aware to advertisers on the platform that users have poor attention spans. With the large amount of video content, nearly 50% of users find it stressful to watch a video longer than a minute and a third of users watch videos at double speed.

Content concerns
Concerns have been voiced regarding content relating to, and the promotion and spreading of, hateful words and far-right extremism, such as anti-semitism, racism, and xenophobia. Some videos were shown to expressly deny the existence of the Holocaust and told viewers to take up arms and fight in the name of white supremacy and the swastika.

The Wall Street Journal has reported that doctors experienced a surge in reported cases of tics, tied to an increasing number of TikTok videos from content creators with Tourette syndrome. Doctors suggested that the cause may be a social one as users who consumed content showcasing various tics would sometimes develop tics of their own.

Content censorship and moderation by the platform
TikTok's censorship policy has been criticized as non-transparent. Criticism of leaders such as Xi Jinping, Vladimir Putin, Donald Trump, Barack Obama, Mahatma Gandhi and Recep Tayyip Erdoğan has been suppressed by the platform, as well as information relating to the Xinjiang internment camps and the abuse of Uyghurs in the region. Internal documents have revealed that moderators suppress posts created by users deemed "too ugly, poor, or disabled" for the platform, and censor political speech in livestreams. TikTok moderators have also blocked content that could be perceived as being positive towards LGBT people.

2022 Russian invasion of Ukraine
In response to the 2022 Russian invasion of Ukraine, TikTok banned new Russian posts and livestreams. However a study by Tracking Exposed found out that TikTok had blocked all non-Russian content, but has continued to host old videos uploaded by Russia-based accounts and permitted Russian state media to continue posting, described as establishing a “splinternet” within a global social media platform. TikTok's vague censorship has permitted pro-Kremlin news but blocked foreign accounts and critics of the war, as a result "Russians are left with a frozen TikTok, dominated by pro-war content".