As part of mental health awareness week, the NHS is talking about its use of online advertising to target individuals who may be suffering from mental health problems but will not reach out for help.
Google, Facebook and Twitter have been criticised in recent weeks for the vast amount of data they collect on their users – allowing advertisers to target them for sales.
Public Health England is running the Good Thinking Service with local authorities and clinical commissioning groups across London to reach out to people suffering from stress and anxiety.
This will signpost sufferers to some of the apps on the NHS Apps Library, run by NHS Digital and NHS England, which is fully launching in autumn.
There were more than 500,000 referrals to NHS psychological therapies for stress and anxiety last year, and the figures on referrals are up 35% in just three years.
The library currently has over 40 apps which help people take control of their own health and care, tackling issues from chronic obstructive pulmonary disease (COPD) to self-harm.
"It's telling that mental health apps make up 28% of the library, yet account for 59% of the visits, with eight out of 10 of the most visited apps in April being for mental health," said Hazel Jones, NHS Digital's Apps Library programme director.
"These days, we consume our information online in ever-increasing amounts and our smartphones sit right at the heart of that.
"If we wanted to give millions of people the tools to take control of their own health, that was what we had to tap into."
The Public Health England apps – which aren't all part of Apps Library yet – look at sleeplessness, anxiety, low mood and stress.
They use social media platforms and Google to target people who have exhibited online behaviours which suggest they might be affected by one of the conditions.
Diarmaid Crean, the deputy director of the digital division at Public Health England, said that the launch was a matter of the NHS engaging with the new century.
He said: "You could argue that the biggest epidemiological databases in the world are our Google searches or our likes on Facebook – to ignore it would be a dereliction of our duty of care.
"In London alone, we know there are around two million people who will experience mental ill health this year and three quarters of those will not get any support."
Figures released by mental health charity MQ last year suggested that over 40% of individuals considered anxiety and depression an inevitable part of life.
"These are the ones that need help but will never seek out services," said Mr Crean.
"We also know that 95% of Londoners are online, which provides an opportunity to reach them outside of the usual care settings.
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"By creating programmes that target messages at those that are likely to be experiencing mental ill health, we can assist them to find the help they need themselves.
"We don't handle any personally identifiable data at any point – it works like commercial ads."