Teenagers spend an average of 31 hours a week online and nearly two hours a week looking at pornography, according to a study.
They spend some three and a half hours communicating with friends on MSN, and around two hours on YouTube and in chat rooms.
Just over an hour is devoted to looking up cosmetic surgery procedures such as how to enlarge breasts and get collagen implants, an hour and a half is spent on family planning and pregnancy websites and one hour 35 minutes is spent investigating diets and weight loss.
One in four teenagers of the 1,000 polled said they regularly spoke to strangers online but thought it harmless.
One in three admitted trying to hide what they were looking at if a parent entered the room.
But children also use the internet to help them with homework, with at least three hours a week spent searching for such information.
The research was conducted by www.cybersentinel.co.uk, which provides software solutions allowing parents to block access to certain sites.
Spokesman Ellie Puddle said: "The alarming thing is the survey shows teenagers are obviously exploring all sorts of topics as a result of modern-day pressures.
"Talking to friends on social networking websites can be completely risk-free, good fun. But there is also the danger of online predators.
"Teenagers and parents need to realise the dangers of talking to strangers online but parents must not overreact by denying access to the internet. The internet is a fantastic resource for learning and development."