How SPF Ratings Work

applying sunscreen; UW Health Transformations Jeune Skin Care; SPF ratings; Madison, WisconsinIf you're uncertain about what the SPF number stands for in your sunscreen, you're not alone. The Sun Protection Factor system (SPF) measures the length of time a sunscreen will protect your skin from burning/reddening from the UVB rays, compared to how long it would take your skin to burn without any sunscreen protection.


To determine the protection level of a sunscreen, multiply the SPF rating by the amount of time it takes your skin to develop burning/reddening from the sun. This will vary from person to person.


If it takes 10 minutes without any sun protection for your skin to begin reddening, using an SPF 15 would theoretically prevent reddening 15 times longer (10 x 15 = 150) - 150 minutes or 2 ½ hours.


Using an SPF 30 would mean 30 times longer (10 x 30 = 300) - 300 minutes or 5 hours.


To maintain SPF, reapply sunscreen every 2 hours (even with high SPF) and right after swimming. The Skin Cancer Foundation recommends SPF of at least 15, which blocks 93% of UVB rays. While SPFs higher than 30 block only 4% more UVB, it may be advisable for sun-sensitive individuals, skin cancer patients, and people at high risk for developing skin cancer.

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Remember that the current rating system only applies to UVB rays. It is important to find a "broad-spectrum sunscreen," meaning it shields against most UVA rays as well as UVB rays. Look on the label for these UVA protecting ingredients: 

  • Zinc oxide
  • Titanium oxide
  • Avobenzone
  • Mexoryl sx

To sum it up, it is best to find a broad spectrum SPF of 15 or greater and reapply every 2 hours! 


Jeune Skin Care Sunscreens


View our line of sunscreens from Obagi, Revision and SkinCeuticals, and throughout July 2017, get 20% off our sunscreens. Stop by UW Health Transformations, 2349 Deming Way in Middleton:

  • Monday and Wednesday: 8am-7pm
  • Tuesday, Thursday and Friday: 8am-5pm