Sun Protection Factor (SPF)

Many of us do not understand what the term SPF really means. I know that the higher the SPF labeled on the sunscreen, then the better protected I am form the sun, or is it? Most doctors recommended we apply a sunscreen of between SPF 15 and SPF 30. But there are sunscreens out there that have an SPF of 70+. So does it offer me maximum protection from say the sunscreen with SPF 15. I always used to wonder about this recommendation. If there are products with higher SPF’s, then why don’t doctors recommend the higher SPF.

SPF is the measure of a sunscreens ability to prevent UVB rays – which cause sunburn, from damaging the skin. The SPF number is a rating that determines how long you can stay in the sun without burning. It does not indicate the quality of protection, just length of time. The amount of time it takes you to sunburn depends on your skin type, and the SPF number you need depends on how much time you expect to be outdoors. Remember that if you will spend time in water, then you need to reapply the sunscreen at least every two hours for it to be effective. Click here to view a chart on SPF values for various skin types on various levels of sun intenisty.

So, here is the reason why I think doctors only recommend a sunscreen of between SPF 15 and SPF 30. SPF protection does not actually increase proportionately with a designated SPF number. For example, SPF 4 blocks 75 percent of sunburn damage; however, it may not provide broad-spectrum protection (protection from both UVA and UVB rays).

A sunscreen containing SPF 15 blocks about 94% of UVB rays, SPF 30 blocks about 97%, SPF 45 blocks about 98% and an SPF 70 blocks about 98.6%. Sunscreens with higher SPF ratings block slightly more UVB rays, but none offers 100% protection. The difference in sunburn protection between medium SPF and high SPF is not that great. Most products with an SPF 15 or greater will provide broad-spectrum protection against both UVB and UVA damage. Remember to check for one or more of these UVA-protecting active ingredients – titanium dioxide, zinc oxide, avobenzone (also called butyl methoxydibenzyl methane), Tinosorb, or ecamsule (Mexoryl) when buying your sunscreen.

It’s very important that you know the amount of time it takes you to sunburn. Generally, people of Caucasian origin, tend to sunburn easily and faster than those of African origin, mainly due to the presence of melanin. Below is a calculation to help you determine the sunscreen you need to use. A sunscreen with SPF 15 will protect you 15 times the time it takes you to sunburn. An SPF 30 protects you 30 times and so on and so forth.

Say it takes me 2 hours or 120 minutes to burn while I’m out in the sun.

  • SPF 15 x 120 minutes = 1,800 minutes or 30 hours of protection
  • SPF 30 x 120 minutes = 3,600 minutes or 60 hours of protection
  • SPF 45 x 120 minutes = 5,400 minutes or 90 hours of protection

As always the best way to make sure that you are well protected is to reapply sunscreen often, especially if you plan to spend a lot of time outdoors. Also apply sunscreen liberally.

Important: Please remember to make sure that your sunscreen product has one or more of the ingredients mentioned above and also check the expiration date on the product. There are a lot of products in our local shops that claim to be sunscreens yet do not contain any of these ingredients.

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Prisca Mwangi is a Beauty Consultant at The Color Palette Company. She can be reached at