During the hot summer days, people will engage in various kinds of outdoor activities and water sports. When staying outdoors, we should take the necessary protective measures to reduce the harmful effect of ultraviolet (UV) radiation to our skin. What are the effects of UV radiation to us? What protective measures should we take?  Some tips for protection against sunburn are discussed below for your reference.

UV radiation can be classified as UVA, UVB and UVC according to the energy or wavelength. UV radiation reaching the earth's surface consists mostly of UVA and some UVB, as all UVC and most of the UVB are absorbed by the atmosphere.  Studies suggested that UVA is responsible for the ageing, wrinkling and immediate tanning effects, as well as potential development of skin cancer. Over-exposure to UVB may cause sunburn and is one of the major causes of skin cancer.

The World Health Organization estimates that about 80% of skin cancer and up to 20% of cataracts may be due to UV over-exposure. Therefore, one must not underestimate the potential harm UV over-exposure may bring.

To reduce the harm from UV radiation, the most important thing is to minimize direct exposure of the skin and the eyes to sunlight.  On days when the UV index is high, we should avoid staying outdoors for prolonged periods.  If you must be out in the sun, take the following precautions:
- Apply sunscreen lotion
- Use an umbrella
- Wear long-sleeved and loose-fitting clothing
- Wear a broad brim hat
- Wear UV blocking sunglasses

Sun Protection Factor (SPF) is a measure of the degree of protection against UVB radiation provided by sunscreens. It relates to how long, on a sunny day, it takes to get burnt by the sun's UVB radiation. For instance, SPF 15 means that with sunscreen lotion on, it will take 150 minutes to produce a detectable burn on a person who gets sun burnt in 10 minutes.

The SPF of a sunscreen lotion only tells us the time extension before a person gets burnt by UVB, but not UVA. An international standard has yet to be developed for protection against UVA, although the PA (Protection Grade of UVA) is usually used in Asia. There are 3 PA grades: PA+, PA++, and PA+++, with each additional plus (+) indicating a higher protection. So, when buying a sunscreen lotion, one should note the SPF as well as the PA.

Up to 80% of solar UV radiation can penetrate thin cloud cover. There are also occasions when broken clouds enhance UV radiation by reflection from their sides. In case of doubt, it is advisable to check the latest UV index through radio, television, the Observatory's website and Dial-a-Weather system (1878200).