It’s old news: UV rays cause all kinds of skin damage — so wearing sunscreen is a must. But like so many other skincare truths, the rule only scratches the surface. We have all kinds of questions: what’s the difference between UVA and UVB damage? Are ultraviolet rays really all that bad for us? Spoiler alert: yes, and no.

We’re taking a deep dive to learn what UV radiation really does to your skin.

6 minute read

What is UV radiation?

Time for a science class flashback: remember the electromagnetic spectrum? We didn’t either, so we looked it up. Basically, it’s the range of different types of energy present on Earth that travels in waves — from the energy that’s visible (like your desk lamp) to the waves you hear (like the radio frequencies), to those mysterious, invisible ones that heat your food (like microwaves).

The spectrum of electromagnetic radiation decreases in wavelength and increases in energy and frequency as you move along. Here’s the breakdown, if you’re curious:

• Radio waves (longest wavelength/lowest energy)
• Microwaves
• Infrared
• Visible light
• Ultraviolet
• X-rays
• Gamma rays (shortest wavelength/highest energy)

Ultraviolet energy (UV radiation), which falls just between visible light and X-rays, was first observed by German physicist Johann Wilheim Ritter in 1801. Scientists have been studying UV rays ever since, discovering their ability to sterilize bacteria in 1878, and their damaging effects on DNA in 1960.

What are the different types of UV radiation?

Approximately 77% of the ultraviolet waves emitted by the sun are absorbed or blocked by our atmosphere. You’ve probably heard of at least two types of ultraviolet rays, but there are actually 3 main UV varieties:

• UVC: shortest wavelength, highest energy, completely absorbed by the ozone layer and the atmosphere
• UVB: medium wavelength and energy, mostly absorbed by the ozone layer
• UVA: longest wavelength UV, lowest energy, not absorbed by the ozone layer

How do UV rays damage skin?

Ultraviolet radiation has both acute and chronic effects on the skin — most of which are damaging, but research is continually revealing the complexity of the relationship between our skin and the sun. Here’s a breakdown:

Acute skin responses:

• Erythema (aka sunburn)
• Photodamage
• DNA mutation
• Immunosuppression
• Vitamin D synthesis
• Tanning

Chronic skin responses:

• Photocarcinogenesis (aka skin cancer)
• Photoaging

You may have heard dermatologist Dr. Sandra Lee (aka Dr. Pimple Popper) talking about the simple way to remember how the two types of UV radiation affect our skin: UVA stands for aging rays, while UVB stands for burning rays.

Let’s delve into the details.

How do UVB rays damage skin?

In the early 1900s, scientists discovered a correlation between sun exposure and skin cancer. Soon after, UVB radiation was linked to sunburn — and an assumption was made that this was the sole cause of skin cancer. The result spurred two developments: the quest to develop a UVB sunscreen, and the long-held myth that tanning — as long as it didn’t lead to a sunburn — was healthy.

Characteristics of UVB rays

• 280-320 nm 
• Shorter-wave 
• Higher energy
• Mostly absorbed by the ozone layer (protection is decreasing with ozone depletion)
• Filtered by window glass
• About 5% of the UV radiation that reaches skin

Effects caused by UVB rays

• Penetrates only into the epidermis
• Directly absorbed by DNA, resulting in structural damage
• Synthesis of Vitamin D
• Photodamage
• Sunburn
• Immunosuppression
• Skin cancer

We’re all familiar with the sunburn-inducing effects of UVB rays, but research has shown that even suberythemal levels (aka below sunburn doses) of UVB rays lead to immediate DNA changes in human skin.

Let’s unpack some of these other damaging effects, like immunosuppression. Scientists speculate that this UV-induced reduction in immune response may be a unique adaptation: preventing the immune system from reacting to all of the chemical byproducts created by ultraviolet rays may help prevent autoimmune disease. However, it also makes it easier for skin cancers to develop.

Here’s where things get even more complicated: UVB rays are responsible for the formation of vitamin D — essential for healthy humans. The chemistry is complex, but involves a series of reactions that begin in the epidermis and end in the liver. Experts say that striking a balance between sun safety and controlled exposure for adequate vitamin D production is the key — but may not be possible for everyone. Depending on how much natural sunlight your geographical region receives, supplementing may be a good option.

How do UVA rays damage skin?

While scientists had linked UVB rays to both sunburn and skin cancer by the early 20th century, it wasn’t until the 1970s that the skin damaging effects of UVA were discovered. 

Characteristics of UVA rays

• 315-400 nm 
• Long-wave
• Lowest energy
• Not absorbed by the ozone layer
• Not filtered by window glass
• About 95% of the UV radiation that reaches skin

Effects caused by UVA rays

• Penetrates deeper to reach into the dermis
• Generates reactive oxygen species (ROS)
• Creates single-strand DNA breaks and DNA protein crosslinks (DPCs)
• Tanning (increased melanin production)
• Immunosuppression

Let’s decode what exactly is going on with UVA-induced DNA damage. You might remember from our articles about free radicals, antioxidants, and skin aging that both normal cell metabolism and environmental damage (in this case, UV radiation), lead to chemical reactions within our skin that create highly unstable molecules: the reactive oxygen species (ROS). These molecules are especially eager to bond with other molecules inside our skin — but this creates a host of problems and interferes with normal cell function. Essentially, these ROS are pretty much going rogue, sabotaging healthy skin processes.

Our bodies have complex systems in place to manage and mitigate the effects of ROS, but these safeguards become overwhelmed from things like stress, excess sun exposure, poor diet, lack of sleep — basically, modern life. DNA is just one of the casualties of ROS overload: the destructive molecules can break the double-helix structure, and they can also cause non-DNA proteins to bind to DNA. These so-called DNA protein crosslinks (DPCs), along with DNA breaks, distort the DNA and prevent it from faithfully replicating. In turn, these mutations cause structural and functional problems, including cancer.

What’s the best way to prevent UV damage?

According to Dr. Lee, there are many options for minimizing damage from UV radiation. Here are her top tips:

• Wear protective clothing: look for fabrics rated with an ultraviolet protection factor (UPF)
• Seek out shade: stay out of direct sunlight when possible, but know that scientists estimate that as much as 50% of UVA exposure occurs in the shade
• Avoid peak hours: plan outdoor activities for earlier in the morning or later in the day
• Use sunscreen: apply (and reapply regularly!) a broad-spectrum sunscreen like SLMD Dual Defender SPF 30. It's formulated for all skin types, including acne prone.

Dr. Lee’s last word

More and more research is showing just how damaging both UVA and UVB rays can be to our skin — both in the short term and later on down the road. It’s why I always say that sunscreen is really the number one skincare product everyone should be using.

—Dr. Sandra Lee