So-called selfies may seem like harmless fun mixed with more than a smidge of narcissism. But, the obsession among today’s young people with snapping and posting self-portraits is driving a rise in eating disorders, says a leading UK expert.

Dr. Alex Yellowlees, psychiatrist at The Priory Group, one of the UK’s biggest eating disorder treatment providers, says young people today are more exposed to pressures to be thin due to a rising trend of people posting photos of their weight loss and starvation “progress” online.

The Priory Group has seen a 15% increase in adult patients seeking treatment for eating disorders in the last year. Though young people still make up the highest percentage in treatment, the number of middle-aged patients with eating disorders has nearly doubled in a year.

Yellowlees believes people’s pre-disposition towards sharing photos online is contributing to the increase. “Some people will take repeated pictures of themselves at various stages of their illness, and send them to others,” he says. “They want to keep a record of their illness and see for themselves, as it were, the progress they think they are making towards anorexia, but they will also transmit the images to other sufferers on occasions.”

In addition to “selfie culture,” technological advances like smartphone apps which calculate calorie intake and encourage weight loss could be fueling the rise in disordered eating.

Yellowlees also warns about the dangerous influence of “thinspiration” sites, where users encourage each other to starve and indulge in other unhealthy weight loss techniques to achieve low body weight. He says many of these pro-anorexia and pro-bulimia sites are “definitely still active,” even as Internet providers, and popular sites, like Instagram, have made efforts to ban them.

“Eating disorders are like a form of ‘psychological malignancy’ and should be taken very seriously by society,” he says. “This includes anorexia nervosa, bulimia nervosa and binge-eating disorder. The latter is more common as people get into adulthood and is linked to depression.”