Skip to main content
Hong Kong Observatory Brand Hong Kong - Asia's world city
GovHK Traditional Chinese Simplified Chinese Search Search Site Map Contact Us
red dot
Print Version
Back
Print Version PDF Version
What You Need to Know about Ultraviolet (UV) Radiation
Episode three: Sun protective clothing for summer


  1. What factors affect the level of UV radiation protection provided by clothing?
  2. What is the Ultraviolet Protection Factor (UPF) for clothing?
        Written by: LEUNG Wai-hung

      Clothing provides the most convenient protection against UV radiation.  In contrast to sunscreen lotion, clothing is relatively cheap and does not rub off.  One may think that clothing can block UV radiation completely but in fact it may not.  The effectiveness of clothing in protection against UV radiation does depend on a number of factors.

    1. What factors affect the level of UV radiation protection provided by clothing?

      There are a number of factors:

       

      • Tightly woven or knitted fabrics have closer fibre structure and can block more UV radiation.  Thicker fabrics also block more UV radiation.
      • Many dyes can absorb UV radiation and therefore darker colour clothing provides more protection.
      • Over-stretched or worn out garments can allow more UV radiation to pass through their small pores.
      • Wet clothing offers less protection as scattering of light will become less with the presence of water.
      • Clothing treated with UV absorber additives during laundry can give better protection.

         

         content Back to content

      1. What is the Ultraviolet Protection Factor (UPF) for clothing?

        In recent years, the Ultraviolet Protection Factor (UPF) has been introduced as a measure of the protection against UV radiation provided by a piece of clothing.  The higher the UPF value, the better the protection against UV radiation offered by the clothing.  A garment with a UPF of 50 allows 1/50 of the UV radiation falling on the surface of the garment to pass through it.  In other words, it blocks 49/50 or 98% of the UV radiation.  Although the UPF is a useful indicator for choosing sun protective clothing, one should note that it has not been adopted as an international standard yet.


        figure1
        Long-sleeve clothing and
        wide-brimmed hat
        are recommended for sun protection
        figure2
        Example of a label
        showing UPF value
        on clothing
         content Back to content

         Reference:

      1. World Health Organization (WHO) web page: "Is it true that clothing always provides good UV protection?", WHO, 2009.
      2. Edlich R.F., M.J. Cox, D.G. Becker, J.H. Horowitz, L.S. Nichter, L.D. Britt, Theodore J.E., W.B. Long, 2004: Revolutionary Advances in Sun-Protective Clothing - An Essential Step in Eliminating Skin Cancer in our World, Journal of Long-Term Effects of Medical Implants, 14(2) 95íV105, 2004.


      Last revision date: <21 Dec 2012>