UV Radiation – UVA vs UVB vs UVC

Don’t Skip this Section, It’s the Most Important One

First, a little background on UV. This first part is boring, but I need to cover it because it’s very important for understanding sun damage and why so many sunscreens are wrong for us. I promise to make this as painless as possible.

What Exactly is UV?

UV stands for ultraviolet and is a form of light energy. UV is a portion of the electromagnetic spectrum (solar spectrum) that is harmful to us. UV radiation is a proven carcinogen.

Sunlight is composed of visible light, infrared light, and ultraviolet light. UV is the light we need to be concerned with.

UV is measured in terms of wavelength, and the scale used is nanometers (nm).

There are 3 types of UV radiation, which cover different ranges of the light spectrum (measured in nanometers).

  • UVA   (320-400 nm)
  • UVB   (280-320 nm)
  • UVC   (100-280 nm)

You only need to worry about UVA & UVB.

 

UVA  

(320-400 nm)

Typically called the ‘Aging Ray’ (A for aging). This is the part of the spectrum that causes the most damage to our skin.

UVA rays are long wavelength rays. They are longer than UVB and therefore penetrate deeper into the skin – all the way into the dermis (the layer of skin below the epidermis) and into the hypodermis (the layer of subcutaneous fat). Here is a quick overview of the layers of skin.

Why is this a big deal? Because the dermis is 70% collagen and houses most of the collagen and elastin in your skin. Collagen and elastin create a ‘scaffolding’ that holds the skin up and gives it structure. When UVA rays reach collagen and elastin fibers, they become misshapen or dysfunctional, and the ‘scaffolding’ in the dermis collapses. This is why your skin wrinkles and sags.

What most people don’t realize is that UVA is present all the time, rain or shine. UVA rays damage your skin even on a cloudy day. 80% of it passes right through clouds. So it’s a grave mistake to assume you need sunscreen only when you’re outside in bright sunshine or if your skin burns easily. You are vulnerable to the sun’s UVA rays every day. Even if you never burn, UVA rays will still damage your skin.

UVA works insidiously – it inflicts damage you can’t see. The damage is invisible and gradual. The cumulative effects of this damage show up later as thickened, aged skin.

One other thing to remember: UVA penetrates right through window glass. You should wear sunscreen if you spend a lot of time indoors by a window.

UVA is further broken down into 2 sub-ranges, which becomes important later when we look at which sunscreen ingredients are effective:

  • UVA-1  (340-400 nm)
  • UVA-2  (320-340 nm)

UVA rays are strongest when they are at an angle to the earth, approximately between 8 am -10 am and 2 pm – 6 pm.

 

UVB  

(280-320 nm)

Known as the ‘Burning Ray’ (B for burning), UVB is the reason your skin burns.

UVB rays are shorter than UVA, and will therefore travel a shorter distance into the skin than UVA. It primarily inflicts damage on the epidermis (the outermost layer of your skin), then gradually attenuates into the dermis (the layer below the epidermis).

The radiation intensity of UVB is 1,000 times stronger than UVA’s intensity. UVB is more cytotoxic and mutagenic than UVA radiation, directly modifying DNA. Therefore, UVB is the major cause of skin cancer.

Unlike UVA, UVB does not penetrate glass. Glass blocks all UVB.

UVB rays are the strongest when the sun is shining directly down on earth between 10 am – 2 pm.

UVC  

(100-280 nm)

This type of radiation is absorbed by the ozone layer and does not reach the ground. Thank goodness. If for some reason the ozone layer ever disappeared, UVC radiation would literally cook us to death.

 

Why You Should Care About UVA

  • UVA is primarily responsible for aging, damaging collagen & elastin
  • 95% of solar radiation is UVA
  • UVA goes right through clouds and window glass

Because UVA is always present during daylight, you need to wear sunscreen EVERY DAY

Why You Should Care About UVB

  • UVB primarily causes burning
  • UVB is a major cause of skin cancer
  • UVB is stronger during the summer and closer to the equator

Remember, both UVA and UVB cause:

  • skin cancer
  • skin aging
  • burning
  • pigmentation

 

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