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

Written by Emily Wood, MD, Board Certified Dermatologist on July 26, 2022 No Comments

uva vs uvb rays

Although we cannot see or feel it, our skin is constantly exposed to UV radiation from sunlight, even during cloudy days. The sun continuously emits a wide spectrum of light, some of which makes it all the way to earth, and some of which doesn’t. Approximately 95% of the energy that reaches us is ultraviolet radiation, in the form of ultraviolet A (UVA) and ultraviolet B (UVB) rays.

Ultraviolet rays can be dangerous because they are unseen and reach our skin in all types of weather conditions. They can damage skin cells without us ever feeling warm. Tanning beds also emit UV rays and damage the skin just as the sun does.

What’s The Difference Between UVA And UVB Rays?

There are two main types of UV light which reach our skin, UVA and UVB. While these UV rays slightly differ, they both have the potential to cause skin damage.

  • UVA rays have a longer wavelength. These rays penetrate deeply into skin and are primarily associated with aging.
  • UVB rays have a shorter wavelength. These rays only reach the skin’s surface, but are responsible for burning and melanoma, the most dangerous type of skin cancer.

In general, UV radiation harms skin by damaging DNA in skin cells. This can lead to mutations which cause premature aging and in the worst cases, skin cancer.

How Do UVA Rays Affect Skin Health And Appearance?

Both the sun and tanning beds emit UVA rays. These lower energy UV rays form over 90% of the UV energy which reaches the earth. Although UVA rays are less intense than UVB, they penetrate the skin more deeply, into the dermal layer. This results in the following:

  • Tanning: Exposure to UVA rays damages the skin. In an effort to protect itself from further damage, skin darkens, resulting in a tan. Tanning beds also emit UVA rays. Even a light tan is unhealthy, as it’s a symptom of skin damage.
  • Premature Aging: UVA rays penetrate skin more deeply than UVB, which contributes to photoaging, a term for early onset wrinkles.
  • Skin Cancer: UVA rays are responsible for some types of skin cancer. Although UVA is less intense than UVB, it penetrates further into the skin where it can damage DNA.

UVA rays are the same strength year-round and can penetrate windows and clouds, making sun protection necessary even on cloudy days. Front car window shields are required by law to block UVA rays but side windows and sunroofs typically do not. Consider installation of professional ceramic window tint for your car to block 99% of UVA and UVB rays.

How Do UVB Rays Affect Skin Health And Appearance?

UVB rays are more high energy than UVA. They can only penetrate the outermost layer of the skin. This results in the following:

Burning: UVB rays damage the skin’s outer layer, resulting in tanning, but also sunburn. Severe sunburn can lead to blistering and permanent scarring.

Skin Cancer: Because they damage skin cell DNA, UVB rays are responsible for several types of skin cancer, including the most dangerous type, malignant melanoma.

Premature Aging: While UVB rays are more frequently associated with skin cancer versus aging, they still contribute to fine lines and wrinkles resulting from sun exposure.

The intensity of UVB rays fluctuates depending on the type of year. They are strongest during the sunniest months but can still cause damage during the winter, especially if sun is reflected off surfaces such as ice or snow. UVB rays do not penetrate through glass windows.

What Are UVC Rays?

UVC rays have even shorter wavelengths than UVB. This gives them the potential to cause the most damage. UVC rays, however, are mostly filtered out by earth’s ozone layer and rarely reach our skin.

Damage from UVC rays tends to be caused by man-made sources including welding torches, mercury vapor lights and intense, bacteria-killing lights. It should be noted that UVC sterilization lamps have been shown to induce DNA damage in human skin.

Exposure to these sources may result in damage to the eyes and skin and can lead to burns, blisters, lesions and ulcers.

Are There Benefits to UV Light Exposure?

Exposure to UVA and UVB light is not only negative. UVB exposure is involved in the synthesis of Vitamin D, an important component of skin and hair, muscle and bone health. One can obtain Vitamin D through eating fortified cereals and orange juice, fish liver oil, flesh of fatty fish, cheese, and egg yolk, as well as, Vitamin D supplements.

Both UVA and UVB light are also used in phototherapy. Also called light therapy, narrow band UVB phototherapy is used to treat skin conditions such as psoriasis and eczema. There is some risk of skin cancer with long term treatment.

How Can I Protect My Skin From Both UVA And UVB Radiation?

The only way to ensure your skin is protected from UVA and UVB damage is to stay out of the sun. If you must be in the sun, the following protective measures can help reduce your risk.

Limit Exposure: The sun is strongest between the hours of 10am and 4pm. Try to schedule outdoor activities outside of this time window.

Wear Protective Clothing: Protective clothing is more effective than sunscreen. Choose tightly-woven fabrics and wide-brimmed hats that are UPF rated. A regular t-shirt has an spf of about 5.

Use Sunscreen: Non-comedogenic, mineral-based sunscreen won’t cause your skin to break out. If you’re swimming or sweating, reapply every 1-2 hours. While some sunscreen is water-resistant, there is no water-proof sunscreen. Most sunscreen protect against UVB rays. To protect against UVA rays, choose a “broad spectrum” sunscreen that specifically mentions both UVA and UVB.

SPF stands for Sun Protection Factor. SPF is a measure of how much UV radiation is required to produce sunburn on protected skin (i.e., in the presence of sunscreen) relative to the amount of solar energy required to produce sunburn on unprotected skin. This means an spf of 15 allows one to be in the sun 15 times longer (when applied in adequate amounts) before reaching the same level of sunburn in unprotected skin. One should also know that most consumers do not apply adequate amounts of sunscreen to achieve the spf that is printed on the sunscreen bottle. The amount of sunscreen required to adequately cover an adult body is about a shot glass worth of sunscreen.

Finally, yes sunscreen can go bad. Always make sure to use relatively new (non-expired) product.

Shop our collection of sunscreens for Texas summer fun!

Emily Wood, MD

Emily Wood, MD is a board-certified dermatologist and fellowship-trained cosmetic dermatologic surgeon specializing in the practice of both cosmetic and medical dermatology. Dr. Wood is an expert in the use of lasers to improve a variety of medical and cosmetic conditions including acne, rosacea, scars, acne scars, birthmarks and wrinkles. She specializes in skin rejuvenation therapies, including neuromodulators (such as Botox and Dysport), fillers, liposuction, sclerotherapy, skin tightening, treatment of cellulite and rejuvenation of the aging chest, neck and hands.

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