The Difference Between UVA and UVB Rays

Hi everybody, I wanted to share a blog entry that I originally posted a few months back on my personal blog Organiworks.  As you know from my previous posts on Edison’s Desk, I work on solar projects here at Global Research.  Helping the environment isn’t just something I do for a living, it is true passion of mine (which is also why I am involved in the group at work “We C… Green.”)  Being the ecological advocate that I am, I’m also super careful about organic food, safe cosmetics. I started the Organiworks blog in effort to document my research on all things organic and natural as well as help readers find the information quickly and easily. Having done solar research for the past few years makes me appreciate the splendid power of the sun. When I had my baby in March, I became increasingly aware of the harmful effects of the sun particularly on skin. Check out my blog for more tips on natural skin care!


Summer is here and we all love to spend time outdoors. Some sunshine is good for us, we all need Vitamin D. But how much is too much? And how do we protect ourselves with safely and effectively? To select the best sunscreens, first we should understand the sun’s radiation. There are two types of ultraviolet radiation we need to protect our skin from, UVA and UVB.

What’s the difference between UVA and UVB?
UVA is ultraviolet radiation between 400-320nm wavelength and UVB is between 320-290nm wavelength. The shorter the wavelength, the higher the energy of radiation. UVA rays account for 90 to 95% of UV radiation that reaches the earth. While UVB makes up only 5-10% of solar radiation, its high energy damages surface epidermal layers and causes sunburn. UVB is strongest between 10AM and 4PM, from April to October and do not significantly penetrate glass. UVA is present equally throughout the daylight hours and throughout the seasons, and can penetrate cloud and glass. UVA penetrates deeper layers of skin and causes tanning. However, both types of UV rays can cause skin cancer because they damage skin cells and alter their DNA. Both types of rays also contribute to premature aging of skin.

What is SPF?
SPF stands for Sun Protection Factor. It is a measurement of the number of times it takes for skin to redden under UVB radiation with the sunscreen compared to no sunscreen. For example, SPF 15 means that it takes 15 times for skin with the sunscreen to redden compared to no sunscreen. As a rule of thumb, a SPF15 sunscreen screens 93% of the sun’s UVB rays; SPF 30 protects against 97%; and SPF 50, 98%. Health professionals agree that at least SPF15 is needed for adequate sun protection. However, a high SPF number doesn’t necessarily mean that the sunscreen also protects against UVA rays. And just because the sunscreen has a high SPF number, it doesn’t mean it’s safe to stay out in the sun longer.

Types of sunscreen ingredients: Physical and Chemical
Physical sunscreens are particles that reflect sun’s rays away from skin. Two are approved by the FDA: Titanium Dioxide and Zinc Oxide. Both of them offer protection against UVA and UVB rays.

Chemical sunscreens form a thin layer on top of skin and absorb UV rays before they reach the skin. The downside of chemical sunscreens is that some of them form free radicals and can contribute to skin aging, cause  irritation, allergic reactions, and possible long term health effects. The FDA approves 17 active ingredients for sunscreens, 15 of which are chemical sunscreens. Some are powerful free radical generators, estrogenic, mutagenic, and may even cause skin cancer.

FDA-Approved Sunscreens
Active Ingredient/UV Filter Name Range Covered
UVA1: 340-400 nm
UVA2: 320-340 nm
UVB: 290-320 nm
Chemical Absorbers:
Aminobenzoic acid (PABA) UVB
Avobenzone UVA1
Cinoxate UVB
Dioxybenzone UVB, UVA2
Ecamsule (Mexoryl SX) UVA2
Ensulizole (Phenylbenzimiazole Sulfonic Acid) UVB
Homosalate UVB
Meradimate (Menthyl Anthranilate) UVA2
Octocrylene UVB
Octinoxate (Octyl Methoxycinnamate) UVB
Octisalate ( Octyl Salicylate) UVB
Oxybenzone UVB, UVA2
Padimate O UVB
Sulisobenzone UVB, UVA2
Trolamine Salicylate UVB
Physical Filters:
Titanium Dioxide UVB, UVA2
Zinc Oxide UVB,UVA2, UVA1

The only downside to physical sunscreen formulations is that they tend to leave white streaks on skin and are thicker so may take longer to apply. However, since physical sunscreens are particles, they do not get absorbed into skin like chemical sunscreens do. They also don’t react or release any potentially harmful by-products, and can be easily washed off. Physical sunscreens are really be best choice because they are low risk and offer wide-spectrum UV protection.

Sun Protection Tips
Staying out of the sun by using shade and tightly meshed clothing is your best protection against damaging UV rays. However, when sunscreens are needed, opt for one that contain both zinc oxide and titanium oxide as active ingredients, together they protect against both UVA and UVB rays. Look for SPF15 or higher for everyday activities such as a stroll in the park; opt for SPF30 or higher for physical activities such as swimming or running. Also remember to re-apply every 2 hours to ensure adequate protection. For babies under 6 months, it’s best keep them out of sun altogether.

A nice natural sunscreen I like is Aubrey Natural Sun Sunscreen SPF 30+ , rated as 1 for low risk by EWG’s Cosmetic Database and listed as one of the best sunscreens for sport and beach. Check out the EWG’s list of best sunscreens for more great natural products.

The Skin Cancer Foundation
Environmental Working Group Sunscreen Guide 2011
Knowland et. al. FEBS Letters “Sunlight-induced mutagenicity of a common sunscreen ingredient” (1993)


  1. Hong Choo

    What about sunblock by SUNPLAy? ARE THEY GOOD ENOUGH PROTECTION.?

  2. Jane Stack

    We need the sun for our health!! Why are you saying the rays are dangerous?? Only the people selling dangerous sunscreen tend to speak like this. Everyone knows that if you are sensitive to the sun and burn easily its because of bad diet and toxicity in the body. Where did you get the idea the Sun is bad for you?

  3. Diana Hamer

    I just start light treatment for ezcema and atop dermatis I hope this helps me because I have been itching for 4 years and have been to other dermatology who said there was nothing wrong with my skin finally i when to a dermogist who done a biopsy and it cam back as atomic and ezcema I been on zolair for itching and also was going to a allergy doctor alli know is I been thinking about doing something about the doctor who said nothing was wrong she didn’t even touch me she said I can see if something was wrong it so sad that Doctors are not like they use to be

  4. Jesse Brito

    Sungazing has taught me that we need both uva & uvb. Truthseekers. Cancer comes more from using sunscreen. The sun entering your eyes help the body produce it’s own sunscreen. Truthseekers. To read sunscreen bottle you need a degree in science.

  5. Tim

    “Natural” sunscreens use metal oxides as filters. Some are photocatalytic active, and will emit a hefty dose free radicals…

    Easy to test: put sunscreen on your palm, and apply your palm on a coated surface such as automotive or coil. A photoactive sunscreen will damage the coating, and your palm shape will be imprinted onto the coating after sun exposure!

  6. frank

    excellent information

  7. bob

    YOU SUCK LOSER THISIS DUM jk it is great

  8. Swati

    Will we use suncream in the both day and night time because I am having tanning.

  9. vivian

    actually uva rays is not linear throughout the day. more constant than uvb but time of day and seasonal variations do exist.

  10. renee

    i needed to know what does UV-A do to your skin. i am doing a science project on it and u didn’t give all imformation.

  11. Jessi

    What do you know about natural oils with spf values with respect to uva & uvb? For example, Shea butter, coconut poul, carrot seed oil, red raspberry seed oil.

  12. Donna Zimmerman

    my comment is below my name.

  13. Donna Zimmerman

    I am so upset right now from learning that my time in a light box at my dermatologist office has done a lot of harm to my skin. I have been going for treatment for Mycosis Fungoides about 20 yrs now ,if not longer, not telling me that my skin would age at an earlier age, which it has. Is there anything to get to help rid my arms,,legs,neck & face of wrinkles. My arms are the worst so far. This is very upsetting to me and has been for a long time. I talked to my Dr. about this and all she said is it’s my age and now I read this. Can you advise me on what to do. Thank You Donna Zimmerman