Sun Protection Factors (SPF)

The SPF is a measurement of the effectiveness of sunscreen. As the SPF increases the more protection the sunscreen gives against UV-B, which is the ultraviolet radiation that causes sunburn, and is a risk factor for skin cancer, and premature skin aging.

The SPF is the amount of UV-B radiation required to cause sunburn on skin with the sunscreen on, relative to the amount required without the sunscreen. For example, if you wear SPF 20, your skin will not burn until it has been exposed to 20 times the amount of UV-B that would normally cause it to burn.

As well as UV-B there is UV-A solar energy, which causes invisible damage to the skin, so that there is no visible tanning or burning. However UV-A is responsible for skin cell damage, which increases the risk of skin cancer. Conventional sunscreen does not block the majority of UV-A radiation, however more recent broad spectrum sunscreen protects against UV-A and UV-B. The very best UV-A protection is provided by products that contain zinc oxide, avobenzone, and ecamsule.

When purchasing as sun protection product it is important to buy one that protects against UV-A and UV-B. The SPF that an individual will require depends on:

  • The skin type
  • Intensity of the solar energy, for example during the midday the sun is much stronger that morning and evening
  • The amount applied and frequency of re-application.
  • Activities in which one engages (for example, swimming leads to a loss of sunscreen from the skin).
  • Amount of sunscreen the skin has absorbed.

Some products are perfumed or contain other products such as insect repellant and after sun soother. These may lead to an allergic reaction or irritation of the skin if you are sensitive to any of the chemicals, so it is best to try a small sample before spending a lot of money on one particular brand.

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