Nine in every 10 teenage boys in Singapore have watched or read sexually explicit materials within the past year, a survey has found, with some first exposed to it even before they start primary school.

In contrast, only 8 per cent of girls - less than one in 10 - admitted to viewing pornography last year, either intentionally or by accident.

Conducted by Touch Cyber Wellness, the main agency that gives online safety talks in schools here, the survey polled 921 students aged 13 to 15 to examine teenage exposure to pornography.

It did the first such survey on teenage exposure to pornography two years ago and followed up with a second one earlier this year.

Compared with the first survey, there is an increase of 6 to 14 per cent of the boys and girls who have been exposed to pornography.

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The main mode of accessing pornographic materials is through personal mobile devices.

Of those who viewed such content, 88 per cent of boys and 73 per cent of girls saw it on their smartphones or tablets. This is an increase of 6 per cent to 8 per cent compared with the 2014 survey.

The earliest age of exposure is upper primary and below for 52 per cent of the boys who accessed such material, and 28 per cent for the girls.

Experts say the findings are worrying as such content can affect children's studies, self-esteem, interpersonal relationships and their attitudes and behaviour towards love and sex. If addiction sets in, it may lead to various forms of dysfunction and sexual crimes.

Touch Cyber Wellness manager Chong Ee Jay called the figures "expectedly alarming".

"This concurs with much of the feedback we have been hearing from the ground in schools and through parents. With kids owning or having access to mobile devices at a younger age, the risk of such exposure is greatly magnified," he said.

Mr Delane Lim, chief executive of Agape Group Holdings which conducts talks and youth camps in schools, agreed. "Exposure to pornography is a given. But we should start getting worried about the average age of kids being exposed to it and the percentage of youth addicted to pornography," he said.

Experts say it is time for parents to monitor and talk to their children about such issues as the exposure rate is expected to only go north, given that Singapore has one of the highest rates of mobile phone use.

When asked how they were first exposed to pornography, 54 per cent of the boys said they searched for it intentionally on the Net while 43 per cent of the girls stumbled upon it while surfing online.

Mr Chong said there is a need to evaluate whether programmes in Singapore effectively let children know that accessing such content is harmful.

Parents can also install Web filters on their child's mobile phone, he added, but this may only work for younger children.

Some recommended filtering and monitoring apps are Mobicip, ScreenTime and OurPact.

Mr Lim said parents must be able to talk to children about such issues.

"But they may not have the moral authority to do so as, ironically, some parents are watching pornography themselves and the children know it," he added.

Madam K. Rosli, 42, mother of a 10-year-old girl and a three-year-old son, said she has not broached the topic with her daughter as it is "sensitive". However, she checks the history of Internet sites and YouTube video sites on her daughter's phone every day.

Said Madam Rosli, an executive: "She hands over her phone willingly every day because we have a curfew for phone use. When the boy grows up, I will get his dad to handle him."