Renee Zellwegger: Fair, burns easily

A poll for the charity Cancer Research UK found that more than 70% of those questioned do not understand the concept of the UV Index.

This is despite it regularly featuring on television weather forecasts.

Over-exposure to sun can trigger malignant melanoma, which kills around 1,700 people in the UK each year.

Accurate measure

The UV Index was developed by the World Health Organization as a way to describe the maximum strength of the ultra-violet radiation from the sun for a particular day.

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It is a more accurate indication of the potential for sunburn than the temperatures forecast each day.

The Index ranges from one (the lowest) to 20 (the highest). However, it is rare for the Index to go above eight in the UK, so the upper limit used in UK forecasts tends to be 10.

People with fair skin need to protect themselves from burning between 11am and 3pm on days with a lower UV Index rating, compared to people with darker skins, who are advised to cover up when the rating is higher.

However, the survey shows 73% of people with fair skin - most at risk of sunburn and skin cancer - admit they still get sun burnt despite almost two- thirds worrying it could lead to skin cancer.

Avoiding skin cancer Stay in the shade Make sure you never burn Always cover up Use factor 15+ sunscreen Promptly consult a doctor over mole changes or unusual skin growths Keep children out of the sun

Jo Viner Smith, manager of the Cancer Research UK SunSmart campaign, said: "These results are quite alarming, especially following the warnings issued recently that we may be in for a heat wave this summer.

"It is particularly worrying that over 70% of people with very fair skin, who are most at risk of skin cancer, do not know what the UV Index is.

Easily burned

"Fair skinned people can burn in as little as 30 minutes when the UV Index is seven and it is important they take extra care at all times of the day when the UV Index is high."

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Cancer Research UK has teamed up with Boots to develop a Celebrity UV Guide, using star skin types as a guide to when people should cover up.

For instance, actor Renee Zellweger is classified as very fair, and will burn easily, when the UV Index is two or higher.

Footballer David Beckham is rated as fair, but will tan. He is at risk when the UV Index is three or higher.

Meanwhile, black stars such as Serena Williams and Will Smith will not burn until the UV Index reaches six or higher.