Feeling tense? It could be your internet connection. A delay of as little as two seconds downloading material to a smartphone is enough to cause users’ stress levels and heart rate to jump, leading telecoms companies have found.

Ericsson and Vodafone monitored the brain activity of 150 volunteers. The results showed that even small delays and disturbances in the speed at which they could access the internet raised their tension levels. This had a direct impact on their loyalty to, and opinion of, their broadband provider.

The subjects in the study in Düsseldorf, Germany, were asked to use their smartphones to complete 13 tasks in ten minutes, including browsing web pages, uploading photographs and watching videos, while moderators cut the speed and quality of their internet service.

A delay of only two seconds uploading a selfie on to a Facebook page was enough to cause significant stress among participants, with users aged 18 to 24 finding the experience much more upsetting than older age groups.

Jasmeet Singh Sethi, senior adviser at Ericsson Consumer Lab, who oversaw the research, said: “We do see that this group is extremely ruthless when evaluating performance. They are extremely impatient and they cannot even tolerate one second of delay. They want content in the blink of an eye.”

Guido Weissbrich, director of network performance at Vodafone Germany, said that the study proved how quickly smartphone users became unsatisfied. “A mere one-second delay has a significant negative impact on the user experience,” he said.