UVA vs UVB rays: what is the difference?


Types of UV rays: UVA and UVB

What is UVA and what is UVB? The sun emits two types of ultraviolet (UV) radiation that reach our skin: ultraviolet A (UVA) and ultraviolet B (UVB). So if you are wondering what does UVA stand for or what does UVB stand for, they stand for ultraviolet A and ultraviolet B. Both types damage unprotected skin, but how they go about doing that differs. Knowing how UVA and UVB rays and their ultraviolet light differs is essential to understanding the need for broad-spectrum sun protection. Read on to find our what is UVB light, what is UVA light and how to protect your skin.

UVA and UVB light are not within the spectrum of visible light that the human eye can see. All light rays, including UVA and UVB rays, have different wavelengths, measured in nanometres, or “nm” for short. To give you some perspective, a nanometre is one billionth of a metre. Some of those rays – like blue light – are visible to us, some aren’t. Now let’s get to UVA vs. UVB and why you need to protect your skin from both!

What is UVA light?

What is UVA? UVA light, also known as long-wave light, accounts for about 95% of the UV light that reaches our skin. Although both UVA and UVB are bad for skin, UVA rays are more of a threat because a much larger percentage of them reach earth’s surface. They’re present all day long, year-round, even when it’s cloudy and the sun “isn’t out.” If you see daylight at any hour, UVA rays are present.

UVA light has a wavelength of 320 nm to 400 nm. There are two types of UVA rays: UVA1 and UVA2. UVA1 light is in the range 340–400 nm; UVA2 light is in the range 320–340 nm. These differences in wavelength are important because specific sunscreen actives work best either alone or in combination with other actives to protect from both forms of UV light.

While some actives like zinc oxide, avobenzone, and ecamsule, provide complete UVA protection without the need for multiple UVA-screening actives, a sunscreen formula can still require other actives to cover the UVB range. As a general rule, regardless of the combination of active ingredients, a “broad spectrum” label on any SPF-rated product is a reasonable assurance* that the sunscreen has been through and passed the testing required to make this claim. This is true for all Paula’s Choice sunscreens.

UVA rays are considered the sun’s silent killers because, unlike UVB rays, you do not feel the effects of UVA rays damaging your skin. UVA rays are the cause of tanning, and unless you burn first, getting a tan isn’t painful – but, those unfelt UVA rays are reaching deep into skin, causing havoc in every layer.

What is UVB light?

Firstly, what is UVB? UVB light has a wavelength of 290 nm to 320 nm, a much smaller range than UVA light. Although not as skin-penetrating or ever-present as UVA rays, UVB radiation is powerful: it’s directly responsible for sunburn and other visible changes to skin’s surface, including discolouration. UVB radiation also plays a role in skin cancers.

Unlike UVA rays, the intensity of UVB rays varies to a much greater degree based on geographic location, time of day, and season. In the northern hemisphere, UVB rays are strongest between April and October, when there are more daylight hours, with peak intensity between 10:00 am and 4:00 pm.

Just like UVA light, UVB light is also present year-round, but UVB rays are more prevalent in sunny climates than in non-sunny climates. UVB light (and UVA light) is reflected from sand, water, and snow (80% of UVB rays reflect from snow!). UVB is also more damaging at higher altitudes than at lower altitudes, which is why skiers and mountain climbers need sunscreen. The same is true for UVA light, with the difference being the higher intensity of UVB when it’s at its most potent.

What is the difference between UVA and UVB?

UVA rays penetrate farther into skin than UVB rays, steadily destroying key substances in skin that give it its firmness and elasticity. UVA rays are a leading cause of wrinkles and a cause of, or major contributor to, every type of skin cancer.

One more difference: UVA rays penetrate glass, while UVB rays do not. Unless the window you sit by at work or the windows in your car are specially treated to filter UVA radiation, your skin is being exposed to UVA rays, making sunscreen an absolute necessity.

The SPF rating of sunscreens is related to protection from UVB rays. To ensure adequate protection from UVA and UVB rays, look for sunscreens labelled “broad spectrum,” which indicates they have been tested and are permitted to make that claim.

Learn more about sunscreen.


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References for this information:

  1. International Journal of Molecular Sciences, January 2015, pages 68–90; and June 2013, pages 12,222–12,248
  2. Experimental Dermatology, October 2014, pages 7–12 PLoS One, August 2014, ePublication
  3. Molecules, May 2014, pages 6202–6219
  4. Indian Journal of Dermatology, Venereology, and Leprology, June 2012 Supplement, pages S9–S14

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