A decade after the Observatory started monitoring skin-damaging ultra-violet radiation and publishing a daily index, fewer than a fifth of children fully understand the harm the rays can cause.
Yet more than two-thirds check the index regularly before joining outdoor activities.
Health and weather chiefs said a survey of more than 3,000 pupils aged 11 and 12 showed the need for more public education.
Health Department senior medical officer Dr Chow Chor-yiu said it was disappointing that fewer than 20 per cent knew that UV radiation could cause premature skin ageing and cataracts. 'Most of the respondents think that skin ageing is natural and not related to sunburn,' he said.
Almost 70 per cent said they would check the UV index as part of their daily lives, but the rest thought this unnecessary and a waste of time.
Observatory assistant director Leung Wing-mo said there was room for more public education.
In the survey, conducted by the Observatory and the department, 3,199 primary five and six pupils from 15 schools were asked about their awareness of UV radiation, readiness to take protective measures and knowledge of its effects. Almost 60 per cent said they would take protective measures before going out, such as using umbrellas and sunscreen. Almost 80 per cent said they knew overexposure to the sun might cause painful sunburn and even skin cancer. More than 80 per cent said they knew the UV level was highest around noon.
'As the effect of UV radiation is cumulative, more attention should be paid to children,' Chow said. 'Schools, parents and students should co-operate to take protective measures.'
Chiao Pong-wai, nine, said: 'I use umbrellas and sunscreen if the UV index is high. I check the index every day before going to school.'
The Observatory recorded high UV-index levels above six on more than 20 days a month between May and September.