SPF, or Sun Protection Factor, increases the length of time you can stay outside in the sun without incurring sunburn or irritation from UV-B rays. At present there is no standard to measure protection from UV-A rays.

Calculate your recommended SPF:

• Rate yourself:
  Select your skin type. The corresponding amount of time indicates how long you can stay safely in the sun before burning.
  Fair skin - 10 minutes
  Olive skin - 15 minutes
  Dark skin - 20 minutes
• Look at the SPF on your sunscreen
  Note which SPF is stated on the product labeling, eg. SPF 20
• Calculate your protection time, the amount of time you can stay outside before burning:
  Multiply the sun safety time for your skin type with the SPF listed on your sunscreen.
  eg. 15 minutes (for olive skin) x SPF 20 = 300 minutes (5 hours) of sun protection
  Result: Olive skin using a sunscreen with SPF 20 can under ideal conditions stay in the sun for up to 5 hours.