UVA vs. UVB Rays: What's The Difference?

By this point, you probably know that you should be wearing sunscreen not just when you’re in the sun but any time you leave the house. However, just like flossing, many people haven’t quite committed to this healthcare habit.

Maybe part of the problem is not completely understanding the importance of protecting your skin from the sun. It can be hard to prioritize something when you don’t completely get why you’re doing it. There’s a lot to learn about how the sun can affect your skin, but a great place to start is knowing about UV light and the difference between UVA versus UVB rays.

What Are UV Rays?

UV light, short for ultraviolet light, is a type of electromagnetic radiation that emanates from the sun all the way to the Earth. UV light is different from visible light rays, which are longer and can be seen by the human eye.

UVA and UVB rays are two types of UV light. Both fall into the “short wavelength” category, meaning they are invisible to the naked eye. Even though they can’t be seen, they can still wreak havoc on our skin.

Hearing the term UV light might conjure up an image of glow in the dark products or black lights, and that isn’t wrong! A blacklight does emit UV light which causes certain objects and colors to glow, and tanning beds use fluorescent bulbs that emit mostly UVA light.

UVA Rays

UVA rays make up nearly 95% of the UV radiation that reaches the earth’s surface, and they are the most powerful category of UV light. They are consistently present during all hours of daylight in every season and can seep through many substances, most notably cloud coverage and glass. Yep, you read that right — clouds and car windows don’t actually prevent UVA rays from reaching your skin.

UVA rays penetrate skin more deeply than UVB rays, reaching through the epidermis (top layer of our skin) and into the dermis (the middle layer of our skin). They’re what help us tan, but they’re also what causes signs of aging like wrinkles and fine lines.

When UVA light reaches our epidermis, it damages the basal and squamous cells (called keratinocytes) in the skin’s basal layer. This is where most skin cancers occur, and damage from UVA rays is known to initiate the development of those cancers.

UVB Rays

UVB rays, on the other hand, primarily cause damage in the epidermis, or the top layer of the skin. They are responsible for causing that painful redness we call a sunburn and play a significant role in causing damage on the skin’s surface. Over time, they can also cause cancer.

UVB rays can reach the earth’s surface (especially high altitudes) throughout the year, but if you are living in the U.S., they are most likely to affect your skin between the hours of 10 AM and 4 PM during the spring, summer and early fall.

So Which UV Rays Cause Cancer?

In a match up of UVA versus UVB rays, which are the most dangerous? The short answer is that they both are but in different ways. While UVB rays can cause visible damage in the short term, leaving you with an uncomfortable burn, UVA rays cause damage in the long run by expediting the signs of aging. In other words, too much exposure to either UVA or UVB rays can cause skin cancer.

How Do I Protect Myself From UV Rays?

Luckily, the answer is pretty simple: by choosing a sunscreen that’s broad spectrum or full spectrum, like SLMD Dual Defender SPF 30. It is a moisturizer doubling as a chemical sunscreen, great for those looking to get sun protection without adding an additional step to their routine. Always make sure that your sunscreen has a minimum SPF of 15, and again, apply it regularly and meticulously.


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