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UV Radiation Information

Health effect and protective measures against UV radiation

Protection against UV radiation

Protective measures against UV radiation
Sun Protection Factor (SPF) for UVB
Protection grade for UVA (PA)
Ultraviolet Protection Factor (UPF) for clothing material

Protective measures against UV radiation
  • 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, you should avoid staying outdoors for prolonged periods.
  • If you must be out in the sun, take the following precautions:

Check the latest UV index and its forecast.

  Wear a broad brim hat.
  Seek shade.
  Wear UV blocking sunglasses.
  Use an umbrella
  Use a broad-spectrum sunscreen lotion blocking both UVA and UVB (with a Protection Grade of UVA (PA) of PA+ or above, and a Sun Protection Factor (SPF) for UVB of 15 or above). Apply liberally and reapply after swimming or sweating.
  Wear long-sleeved and loose-fitting clothing


Department of Health
For more health information related to UV, please visit the webpage of the Central Health Education Unit of the Department of Health.

Sun Protection Factor (SPF) for UVB

SPF is mainly a measure of UVB protection . 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.

SPF is also applicable to other sunburn preventive measures. As a rough guide, the SPF of a broad-brimmed hat is 3 to 6, while that of ordinary summer clothing is 6 to 7. One can see from their SPF values that the degree of protection is not as high as sunscreen lotions (usually SPF 15 or above).


Sunscreen Lotion image
Example of SPF value shown on a sunscreen lotion

Protection grade for UVA (PA)

The SPF on 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.

Skin care product image
Example of a skin care product showing its PA grade

Nash, J.F., P.R. Tanner, P.J. Matts, 2006, "Ultraviolet A Radiation : Testing and Labelling for Sunscreen Products", Dermatologic Clinics, published by Elsevier Saunders, 24, 63-74.

Ultraviolet Protection Factor (UPF) for clothing material

The Ultraviolet Protection Factor (UPF) measures the UV protection provided by fabric. Unlike SPF which is a measure of only UVB protection, UPF rates protection against both UVA and UVB. For example, a garment with a UPF of 50 allows 1/50th of the UV radiation falling on the surface of the garment to pass through it. In other words, it blocks 49/50ths or 98% of the UV radiation. However, an international standard for the concept of UPF has not been developed yet.

"Individual protection against UV: Is it true that clothing always provides good UV protection?", World Health Organization website, 2009.

label showing UPF value on clothing image
Example of a label showing UPF value on clothing











Last revision date: <27 Dec 2012>