Due to varying degrees of elevation of the sun, Lhasa has stronger ultra-violet (UV) radiation in the summer than in the winter. There are more rainy days from July to August than in June, so UV radiation is strongest in June. The number of days rating 5 on the UV index is between 60% and 70%.

Most people can withstand sunshine for 15 minutes

The reporter learned from the Dermatology Department at Tibet Center for Disease and Prevention (CDC) that, UV rays are divided into three categories according to wavelength – UVA, UVB and UVC – each with differing degrees of skin penetration. The lead doctor at the CDC’s Dermatology Department, Kang Ping, told the reporter that, human skin can normally withstand 15 minutes of exposure to sun without any protection. After that, one’s tolerance to the sun’s rays varies with differing skin types, as does the degree of damage to the skin. It is best not to be exposed to the sun for long periods and to make sure you're protected when traveling.

Usually, the strongest UV radiation occurs around 13:00 each day

Tips

When choosing sunscreen, the SPF and PA index are important

According the doctor Kang Ping, there are two types of harm from UV radiation: skin tanned from UVA rays and sunburn from UVA rays.

"There are many measures to avoid skin damage from UV rays. For example, when heading out take an umbrella, sun hat and sunglasses. For best results apply some sunscreen, but make sure it is of good quality to avoid damage to the skin",said Kang Ping.

She added that UV rays reflected onto the ground can also cause skin damage, so taking an umbrella won't keep out all UV radiation.

Kang Ping said: "The SPF index is only resistant to UVB to prevent sunburn while the PA index is resistant to UVA to prevent sun tan. One factor on the SPF index corresponds to 15 minutes of sun resistance. Factor 30 SPF sunscreen can keep the sun out for 7.5 hours. The higher the PA value, the better – the best choice is ‘+++' but ‘++’is also sufficient. "

Kang Ping reminded the public not to use cosmetics containing photosensitive substances, such as perfume. In terms of diet, don't eat too many vegetables containing photosensitive substances, such as lettuce and spinach. "Once the photosensitive substances have been absorbed, damage to the skin is exacerbated when light appears",she said.