How to Understand What SPF Numbers Mean

wolfandmoroko understanding what spf numbers mean

Sunscreens are products that help prevent the sun’s harmful ultraviolet rays from reaching the skin’s surface. Sun overexposure causes sun burn, wrinkles, dryness and inflammatory condition like rosacea and eczema to flare up. The best ways you can protect your skin are wearing sunscreen, staying in the shade, wearing protective eyewear and hats.

Types of UV Radiation

UVA rays are longer wavelength rays that can penetrate through glass windows, get right down to the connective tissue in the skin and cause cumulative skin damage i.e. skin aging, wrinkling and skin cancers. UVA rays are also responsible for about 95% of the UV radiation from the sun that reaches the Earth’s surface.

UVB rays are shorter in wavelength. While they cannot penetrate glass windows, they cause fine lines, dark spots, wrinkles, sunburn and skin cancers. UVB rays are the remaining 5% of the UV radiation reaching Earth, with the majority being absorbed by the atmosphere.

UVC rays are the shortest in wavelength. Don’t worry about these ones since the ozone layer deals with them, absorbing them before they can reach the Earth’s surface.

What is SPF?

It is established that a broad spectrum sunscreen will protect against both UVA and UVB rays. SPF aka Sun Protection Factor is a rating of how much UV light will be blocked.

The amount of SPF that is effective at blocking can be estimated using the following algorithm from dermatologist Dr. Rachel Herschenfeld – 1/(SPF number) of rays goes through. That means:

  • SPF 15 allows 1/15 UV rays, or 6.7% through, blocking about 93.3% of UV rays.
  • SPF 30 allows 1/30 UV rays, or 3.3% through, blocking about 96.6% of UVB rays.
  • SPF 50 allows 1/50 UVB rays, or 2.0% through, blocking about 98.0% of UVB rays.

Generally, a higher SPF number offers more protection from UV light than a lower one. It also makes sense to use a broad sunscreen with a higher SPF  for the following reasons.

What Factors Affect SPF?

  1. Skin type. If it takes 20 minutes of sun exposure to cause unprotected skin to burn, theoretically, SPF 15 would take the skin 15 times longer (15*20=300 minutes) to burn. However, your skin would burn quicker if you are prone to sun burn.
  2. The intensity of the sun. The hotter the sun, the quicker the sunscreen loses it’s effectiveness.
  3. The amount of sunscreen applied. Many people don’t apply as much sunscreen as required in order to get the level of protection on the bottle.On the face alone 1/4 teaspoon of sunscreen should be applied.
  4. External factors. Swimming, towels, clothing can all wipe away sunscreen.

What are some of your favorite sunscreens? Have you tried any Asian brands?

Image Source

Follow my blog with Bloglovin<


12 thoughts on “How to Understand What SPF Numbers Mean

  1. Reblogged this on ItsMayaBee and commented:
    These have been my thoughts and questions lately. I was one of those people who never used sunscreen – and i mean never until end of last year when i did a bit of research and incorporated it in my daily skin routine after seeing the damage i was exposing my skin to. I am currently using all natural coconut oil as my moisturizer which has zero SPF so i mix it with the Neutrogena Ultra Sheer Sunscreen SPF 60.
    I will recommend this sunscreen, not pricey and it has actually done wonders on my skin.

    Go Get That Sunscreen Ladies!!



    Liked by 1 person

  2. Pingback: The Sun in your Eyes: Why your eyes need sun protection | Wolf & Moroko

  3. Pingback: Effective Skin Care for Cancer Warriors | Wolf & Moroko

  4. Pingback: Cosmetics Ingredients Class: Beta Hydroxy Acids 101 | Wolf & Moroko

  5. Pingback: A Guide on Buying UV Protected Sunglasses | Wolf & Moroko

  6. Pingback: A Basic Skin Care Routine for Acne | Wolf & Moroko

  7. Pingback: Cosmetics Ingredient Class: Allantoin 101 | Wolf & Moroko

  8. Pingback: How to Even Your Skin Tone | Wolf & Moroko

  9. Pingback: Love is Understanding…The Structure of the Skin | Wolf & Moroko

  10. Pingback: The Importance of Having a Skincare Routine | Wolf & Moroko

  11. Pingback: The Truth About 4 of the Most Common Cosmetics Claims |

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s