The Differences Between UVA and UVB Rays

Do you know the differences between UVA and UVB rays? Keep reading to discover what scientists have to say on the subject.
The Differences Between UVA and UVB Rays
Diego Pereira

Reviewed and approved by el médico Diego Pereira.

Last update: 04 February, 2023

Ultraviolet radiation (UVR) is a type of non-ionizing radiation that’s emitted by the sun and some artificial sources. As experts point out, continuous exposure to its wavelengths results in inflammatory processes, aging, degenerative processes, skin diseases (more common in summer), and cancer. Today we’ll go over the differences between UVA and UVB rays.

The sun’s rays are the main source of ultraviolet radiation (UVR). Tanning beds are the best example of artificial sources, which are associated with the same complications listed above (under continuous exposure). There are many doubts about the types of ultraviolet radiation (UVR), so the following criteria will be useful for you to understand the differences between UVA and UVB rays.

The difference between UVA and UVB rays: types of ultraviolet radiation (UVR)

Researchers divide ultraviolet radiation (UVR) into three types: A, B, and C. They’re commonly described as UV-A, UV-B, and UV-C; although it’s also common for them to be classified as UVA, UVB, and UVC. The division is made based on the electrophysical properties; in other words, how the wavelengths are conformed according to each case. So, we have the following characteristics:

  • UVA Rays: Wavelengths ranging from 320 to 400 nanometers
  • UVB rays: Wavelengths ranging from 290 to 320 nanometers
  • UVC rays: Wavelengths ranging from 100 to 280 nanometers

In very simple terms, UCV rays are short wave, UVB rays are medium wave, and UVA rays are long wave. The ozone layer blocks UVC rays, so those that predominate below it are UVA and UVB rays. Let’s take a look at their features to better understand how they can impact you.

What are UVA rays?

The differences between UVA and UVB rays are alarming.
Throughout the day people are constantly exposed to UVA rays that can be harmful in the long term.

UVA rays make up 90-95% of the sun’s wavelengths available in the environment. This type of radiation can be divided into two types: UVA I and UVA II. The former oscillate between 320 and 400 nanometers and the latter between 320 and 340 nanometers; so, they’re also known as far UVA and near UVA, respectively.

This type of ray is present throughout the day, regardless of whether it’s morning, afternoon, or evening. They can penetrate most car windows without major complications and there’s evidence that even at low doses, they cause morphological changes on the skin surface. Those of type I penetrate to the dermis, while those of type II reach only the surface of this layer of the skin.

UVA rays are often linked to skin cancer due to DNA damage and inhibition of the protective mechanism within the skin. They can also produce a dozen complications, among which actinic keratosis stands out.

Exposure to high doses generates an immediate tan and sunburn. We know that sunscreen isn’t effective in containing the rays in the face of prolonged and permanent exposure (it is for short and regular exposures).

What are UVB rays?

UVB rays make up 5-10% of the wavelengths of sunlight found in outer space. Almost all rays of this type are absorbed in the upper layer of the skin; that is, the epidermis. Most of them don’t penetrate to the dermis, but they’re charged with greater energy than the previous ones. Most car windows effectively block these rays.

Exposure to UVB rays causes a molecular rearrangement that forms specific photoproducts, mainly cyclobutane and photoproducts 6–4. They can thus generate a tan in the medium term (not immediately), as well as sunburns and blisters.

Often cited as healthy UV rays, this is far from the truth with long exposures. In fact, they’re to blame for most episodes of skin cancer.

Should you use sunscreen?

A woman with sunscreen on her leg.
Using sunscreen daily is essential to avoid health complications derived from exposure to UV rays.

The Centers for Disease Control and Prevention (CDC) recommend an average of 15 minutes of sun exposure 2-3 times per week to receive the associated benefits. Naturally, most people far exceed these recommendations.

It has already been established that despite the differences between UVA and UVB rays, both cause alterations in the skin, so the use of sunscreen is recommended when these suggestions are exceeded.

The effectiveness of sunscreens isn’t disputed by scientists, and they may be the best tool to deal with the consequences of regular exposure to the sun’s rays. Every person who’s directly or indirectly exposed to the sun’s rays should use sunscreen. These block both UVA and UVB rays and should be applied every 2 hours to maintain skin protection.

When buying one, you must take into account the sun protection factor (or SPF). As a general rule, only those sunscreens that have an FPS of 30 or greater are recommended.

Reducing exposure to the sun, covering up with clothing, wearing sunglasses, and wearing hats and caps is also a great help. Regardless of the differences between UVA and UVB rays, you must take these variables into account to avoid complications in the medium and long term.

  • Bens G. Sunscreens. Adv Exp Med Biol. 2014;810:429-63.
  • D’Orazio J, Jarrett S, Amaro-Ortiz A, Scott T. UV radiation and the skin. Int J Mol Sci.
  • Lavker RM, Gerberick GF, Veres D, Irwin CJ, Kaidbey KH. Cumulative effects from repeated exposures to suberythemal doses of UVB and UVA in human skin. J Am Acad Dermatol. 1995 Jan;32(1):53-62.
  • Lowe NJ, Meyers DP, Wieder JM, Luftman D, Borget T, Lehman MD, Johnson AW, Scott IR. Low doses of repetitive ultraviolet A induce morphologic changes in human skin. J Invest Dermatol. 1995 Dec;105(6):739-43.
  • Serpone N. Sunscreens and their usefulness: have we made any progress in the last two decades? Photochem Photobiol Sci. 2021 Feb;20(2):189-244.

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