UVA vs. UVB rays: what is the difference?


The sun emits two types of UV radiation that reach our skin: ultraviolet A (UVA) and ultraviolet B (UVB). Both types damage unprotected skin, but in different ways. Knowing the difference between UVA and UVB rays is essential to understanding the need for broad spectrum sun protection.

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

What you can expect:

  • What is UVA light?
  • What is UVB light?
  • UVA and UVB protection

What is UVA light?

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 the 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 while 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 kinds of UV light.

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 tanned isn’t painful – but those unfelt UVA rays are reaching deep into the skin and causing havoc in every layer.

UVA rays penetrate further into the skin than UVB rays, steadily destroying key substances that give our skin 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.

Another 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. This is why sun cream application is an absolute necessity, even indoors.

What is UVB light?

UVB light has a wavelength of 290 nm to 320 nm, a much smaller range than UVA light. Although not as skin-penetrating and ever-present as UVA, UVB light is powerful. So if you’re wondering: is a sunburn UVA or UVB? It is UVB that’s directly responsible for sunburn and other visible changes to the skin’s surface, like discolourations. UVB radiation also plays a role in skin cancer.

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 AM and 4 PM.

UVB light is also present year-round, but it is much more prevalent in sunnier climates. Sand, water and snow all reflect UVB light, as well as UVA light. Snow actually reflects about 80% of UVB rays! UVB is also more damaging at higher altitudes than lower altitudes, which is why skiers and mountain climbers must wear sun cream. The same is true for UVA light, with the difference being the higher intensity of UVB when it’s at its most potent.

UVA and UVB protection

Some actives like zinc oxide, avobenzone and ecamsule can provide complete UVA protection without the need for other UVA-screening actives. However, an SPF formula can still require multiple actives to cover the UVB range of rays.

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 sun cream has undergone and passed the testing required to make this claim. This is true for all Paula’s Choice SPF formulas.

*Note: It’s been reported in the media that some sunscreens on the market use the broad spectrum claim but when independently tested, they did not actually provide broad spectrum protection. As a result of this, the FDA in the U.S. is increasing its inspection process and devising stricter standardised labelling for broad spectrum sunscreens so consumers will have consistency when shopping and not be misled.

The SPF rating of sun cream is related to protection from UVB rays. For sunscreen with UVA and UVB protection, look for “broad spectrum” labels as it indicates they have been tested and are permitted to make this claim. UVA protection can also be graded using the PA (Protection of UVA) scale, which is common in Asia and Europe.

SPF 30 works great in most cases, however, you might require SPF 50 or higher if you’re spending a lot of time outside or if the UV index measures 8+ that day.

References for this information:

1. International Journal of Molecular Sciences, January 2015, pages 68-90; and June 2013, pages 12222-12248
2. Experimental Dermatology, October 2014, pages 7-12
3. PLoS One, August 2014, ePublication
4. Molecules, May 2014, pages 6202-6219
5. Indian Journal of Dermatology, Venereology, and Leprology, June 2012 Supplement, pages S9-S14


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