What is SPF?

SPF is a near universal label on sunscreens and most of us know that it is a measurement of sun protection. SPF is an acronym for sun protection factor, and is indeed a measurement.

SPF expresses the difference in length of time it takes for a person's skin to be sun-burned without sunscreen, against the time it takes for the same person to be sun-burned with sunscreen. If you can stay out in the sun for 10 minutes in the sun before burning, using a sunscreen with SPF 15, you should be able to stay exposed to the sun for 150 minutes before burning. A sunscreen with SPF 30 would protect the same person for up to 300 minutes.

The limitations of SPF as an accurate measure of product efficacy

SPF is a useful guideline and a measurement of efficacy in the protection that it provides. It does, however, have its limitations. SPF is a number that is produced under laboratory conditions, and countless studies have demonstrated that real-life results may not accurately reflect the protection that the SPF number should provide.

  • SPF measures protection from UVB rays, a spectrum that causes sunburns. Having an SPF rating does not measure protection from UVA light.
  • SPF is measured under laboratory conditions, and does not account for real-life factors that diminish the sunscreen's effectiveness. Some of these factors include erosion from exposure to wind, water, sweat, and towelling, but the most important factor is that the average consumer uses about 25% of the sunscreen used to perform SPF tests.
  • A product with an SPF rating higher than 30 does not add extra minutes of protection in a proportionate manner, as the sunscreen deteriorates from UV light after long exposure, and sunscreen will need to be reapplied to maintain efficacy.

Does SPF matter?

SPF shouldn't be thought of as the sole indicator for a sunscreen product's superiority, but it is a useful measurement of the protection that it provides (only from UVB rays!). SPF still does matter, and a sunscreen product with an extremely low SPF (2-5) will offer small amounts of protection.

These types of products are often found in combination with other cosmetic products such as moisturizers. They may be a useful moisturizer, but understand that as a sunscreen their efficacy is severely limited. On the other hand, there have been recent trends of super-high SPF products offering 70-100 SPF. While there is no harm in using these products, it's important to understand that you will still need to reapply the product due to natural degradation after a few hours. A product with SPF 15 eliminates 92% of UV light and a product with SPF 30 eliminates more than 97% of UV light. You can see from this that higher SPF products will not affect the length of time that one can stay in the sun proportionately.

  • Choose a sunscreen that has an SPF of at least 15. This ensures that the product absorbs or reflects the majority of UV light and is effectively protecting you from the sun.
  • SPF rating higher than 30 will offer diminishing returns in terms of protection versus SPF number, as a product with SPF 30 is already shutting out more than 97% of UV light already. It is not bad to have a high SPF rating, but it is not the only factor to consider.
  • Remember to look for the label "broad spectrum protection" or protection from "UVA rays" as SPF only measures protection from UVB light. Unfortunately there is no standardized way to measure protection from UVA light.
  • Choose a sunscreen that you enjoy using. You may need to take price, texture (dry or sticky), and fragrance into account. Personal preference is an important factor, as users are far more likely to use favorable products more often. Remember that the perfect sunscreen is perfectly useless if it sits in the drawer unused. Regularity of use is often assumed, but is likely to be the most important and neglected factor in sunscreen efficacy.