Why is "online addiction" usually written in quotation marks?

Because it is not a recognised diagnosis. There is no internationally agreed term, no general definition and no official diagnostic criteria that combine the problems around screen use into one independent disorder.

Many terms are used side by side:

• in everyday language: internet addiction, online addiction (Internetsucht, Onlinesucht)
• problematic internet use (Problematischer Internetgebrauch, PIG)
• addictive use of social media or social networking sites (SNS)
• multiple media dependence
• computer game addiction
• addictive online behaviour (suchtartiges Onlineverhalten, the BAG's term)
• problematic screen use or internet-related disorders (internetbezogene Störungen, IBS)

Despite growing research, none of these has become the agreed name for an independent disease. "The internet" is a medium, not an activity: someone can be hooked on gaming, gambling, social media, pornography or shopping, and each works differently. The Swiss expert group therefore wants "problematic / risky screen use" to replace "online addiction" as the umbrella term. In short: "online addiction" as such does not exist; specific problematic behaviours online do.

Go deeper:

• Wikipedia: Internet addiction disorder — the history of the term and the dispute over whether it is a real disorder.