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UV light

UV light is bad news for your skin. And it’s not exactly good news for your eyesight. But what is UV light and why is it dangerous? 

The answers to these questions will help you understand the risks of UV light. Read on for tips on saving your skin and preserving your eyesight.   

What does UV mean? 

UV is short for ultraviolet. In a crayon, violet is a shade of purple. In the scientific world, violet is a wavelength of light that the human brain interprets as purple. Thus, ultraviolet is an extra-high version of the violet wavelength.    

Wavelengths measure the distance between the top of a wave and the top of the next wave. Waves happen at the beach when waves crash into the shore. The wavelength is the distance between the wave that’s hitting the shore and the wave right behind it. 

And, of course, waves happen in space. Sunlight moves in waves traveling at the speed of light (186,000 miles per second, or 670 million miles per hour). All light waves are not the same: Different colors of light have different wavelengths as measured on the electromagnetic (EM) spectrum. 

What is the electromagnetic spectrum?

The EM spectrum measures energy by wavelength. The shortest wavelengths are at one end, middle wavelengths are in the center and the longest wavelengths are at the other end. 

The electromagnetic waves with the shortest wavelengths carry the most energy, and those with the longest wavelengths carry the least energy. High-energy wavelengths include gamma rays and X-rays. Low-energy wavelengths include radio waves and microwaves. 

The human vision system sees only a tiny fraction of the EM spectrum. We call this fraction the visible light spectrum, which is in the center of the electromagnetic spectrum.    

How does the visible light spectrum work? 

The visible light spectrum is red on one end and runs through yellow to green to blue to violet on the other end. Red has lower energy; violet has higher energy. Ultraviolet, or UV, is just beyond the violet section of the visible light spectrum. 

UV rays carry more energy than visible-light waves do, which makes them more dangerous to humans.  

Why is ultraviolet light hazardous? 

Ultraviolet light from the sun triggers chemical reactions when it touches human tissue. Some reactions are good for you: UV light tells the skin to produce vitamin D, which strengthens bones and prevents a bunch of health problems. (Note: You only need about 15 minutes of sun exposure two or three times a week to get all the natural vitamin D your body needs.)

Short-term exposure to the sun tells the body to release melanin, which causes the skin to darken. Skin with high melanin content has better defenses against UV light — but that protection goes only so far. 

The longer you’re exposed to ultraviolet light, the greater the chance that UV radiation will set off a chain of reactions that leads to skin cancer or other problems. By contrast, using sunscreen with a sun protection factor (SPF) of 15 or more will reduce your risk of:

  • Squamous cell carcinoma by about 40%.

  • Melanoma by 50%.

  • Premature skin aging by 24%. 

Skin cancer is easily prevented: Cover your skin and apply sunscreen to exposed areas and you’ll go a long way toward reducing your cancer risk.  

What are the most common varieties of ultraviolet light?

Scientists divide ultraviolet rays into three classes: 

  • UVA – These ultraviolet waves have the longest wavelengths and hence the least energy. This makes them less of a hazard to the skin but more dangerous to the eyes (more on this below).  

  • UVB – These medium-length UV waves tell the skin to release melanin, creating a suntan, which causes little harm. But overexposure to UVB rays causes sunburns, which raise the risk of skin cancer.  

  • UVC – These ultraviolet rays have the most energy, but they’re not the most hazardous to humans. Why? Because the ozone layer in the earth’s atmosphere absorbs UVC rays before they ever touch human skin. 

Sun protection products usually have an SPF rating on the label. SPF measures protection from UVA and UVB — but it’s not foolproof. Using a product with the highest SPF might encourage you to stay out in the sun too long,  defeating the purpose of applying it. 

A better strategy is to use UV-blocking sunglasses and protective clothing (which doesn’t wear off or wash off, like sunscreen does) and use sunscreen on a few small areas of exposed skin.  

How does ultraviolet light damage eyesight? 

The human eye has no skin, so it can’t get skin cancer from UV radiation. But there are plenty of other ways for ultraviolet light to cause vision problems, including: 

  • Cataracts – The eye’s natural lens starts getting cloudy in late middle age, causing cataracts. Too much exposure to ultraviolet light can contribute to cataracts. 

  • Eyelid cancer or eye cancer – The eyes, eyelids and the area around the eye socket can be prone to skin cancer and/or tumors. Eyelids protect eyeballs from physical impact and keep them moist and free of infection, so you can’t afford to neglect them. 

  • Photokeratitis – Also known as snow blindness, photokeratitis happens when ultraviolet light reflected off surfaces like snow cause sunburn on the cornea. This can be extremely painful but vision loss usually is temporary. 

  • Macular degeneration – The macula is in the middle of the retina, the layer of light-sensitive nerves that send vision information to the brain. UV light contributes to degeneration of the macula, whose nerves provide sharp, focused vision. Without this visual clarity, it’s difficult to read or drive a car. 

  • Pinguecula and pterygium – These bumps on the surface of the eye often result from spending too much time in the sun. Pterygium, also called surfer’s eye, can start in the white of the eye and spread to the cornea if untreated. 

These risks illustrate why it’s so important to shield your eyes from ultraviolet light. 

How do sunglasses keep UV light from damaging the eyes? 

The lenses of sunglasses can be manufactured with special materials that block damaging ultraviolet light. All About Vision has extensive resources on sunglasses. Click these links to find out what you need to know. 

  • Sunglasses overview – Learn more about UV light and how sunglasses protect against it. 

  • UV protection levels – Why shades with the UV 400 rating offer the most protection.  

  • UV exposure risks – More on the hazards your eyes face when you’re out in the sun. 

  • Protection testing – Find out how your eyecare professional can assess the protection level of your sunglasses.  

  • Sports and recreation – Get the right eye protection for outdoor competitions and athletic endeavors. 

For your next eye doctor’s appointment, take a moment to ask about protecting your eyes against UV light. Don’t forget to mention prescription sunglasses. They may be just what your eyes need if you spend a lot of time in the sun.

How fast does light travel? | The speed of light. Space.com. March 2018.

Electromagnetic radiation. Nasa.gov. Accessed May 2021.

Sun protection and vitamin D. Skin Cancer Foundation. May 2018.  

Ask the expert: Does a high SPF protect my skin better? Skin Cancer Foundation. June 2020.

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