There is a shocking upward trend in the prevalence of self-harm amongst children and young people. But with extreme pressures on the NHS many teenagers are not getting the help they need. Charity stem4 had developed an app – Calm Harm – to help teenagers resist or manage the urge to self-harm, but with a confusing user journey the app was under-performing. The app was recreated in 2017 with a focus on design and a more engaging user experience. A co-creation process involving teenagers was integral to the strategy and Calm Harm is now more appealing to its target audience; the app’s calming design and its consideration of discretion all resonate. Initially aiming to support 100,000 individuals in the UK, to date there have been more than 800,000 downloads globally. Over 500,000 people have used it more than once and after completing an exercise on the app, 93% reported a reduction in the urge to self-harm. After rigorous assessment, Calm Harm is one of only 18 mental health apps to be included on the NHS Apps Library.