Sunscreen ingredient may pose skin cancer risk, researchers find

As vacationers prepare to spend time outdoors this summer, many of them will pack plenty of sunscreen in hopes it will protect their bodies from overexposure, and possibly from skin cancer. But researchers at Missouri University of Science and Technology are discovering that sunscreen may not be so safe after all.


Cell toxicity studies by Dr. Yinfa Ma, Curators’ Teaching Professor of chemistry at Missouri S&T, and his graduate student Qingbo Yang, suggest that when exposed to sunlight, zinc oxide, a common ingredient in sunscreens, undergoes a chemical reaction that may release unstable molecules known as free radicals. Free radicals seek to bond with other molecules, but in the process, they can damage cells or the DNA contained within those cells. This in turn could increase the risk of skin cancer.

Ma also found that the longer zinc oxide is exposed to sunlight, the greater the potential damage to human cells.

“Zinc oxide may generate free radicals when exposed to UV (ultraviolet) sunlight,” May says, “and those free radicals can kill cells.”

Ma studied how human lung cells immersed in a solution containing nano-particles of zinc oxide react when exposed to different types of light over numerous time frames. Using a control group of cells that were not immersed in the zinc oxide solution, Ma compared the results of light exposure on the various groups of cells. He found that zinc oxide-exposed cells deteriorated more rapidly than those not immersed in the chemical compound.

Even when exposed to visible light only, the lung cells suspended in zinc oxide deteriorated. But for cells exposed to ultraviolet rays, Ma found that “cell viability decreases dramatically.”

When exposed to ultraviolet long-wave light (ultraviolet A or UVA) for 3 hours, half of the lung cells in the zinc oxide solution died. After 12 hours, 90 percent of the cells in that solution died, Ma found.

Why does zinc oxide, an ingredient used in sunscreen to help block harmful UV rays, cause cells to deteriorate when exposed to sunlight? According to Ma, when the zinc oxide nano-particles in the solution absorb the UV rays, the reaction releases electrons, which in turn may produce unstable free radical molecules in the zinc oxide solution. Those free radical molecules then bond with other molecules and act as parasites, damaging the other molecules in the process.

Ma and his colleagues at Missouri S&T published their initial research results in the January 2009 edition of the Journal of Nanoparticle Research. The paper, titled “Toxicity of nano- and micro-sized ZnO particles in human lung epithelial cells,” was the first comprehensive study ever published on this subject. Lead author Weisheng Lin was Ma’s Ph.D. student at the time. Other authors of the paper were Chuan-Chin Huang, a graduate student in biological sciences at the time, and two members of S&T’s biological sciences faculty, Dr. Katie Shannon (assistant professor) and Dr. Yue-Wern Huang (associate professor).

Now, Ma is preparing to publish his latest research results in the journal Toxicology and Applied Pharmacology. A publication date has not been determined.

Ma’s research on zinc oxide’s effect on cells is still in the early stages, so he cautions people from drawing conclusions about the safety or dangers of sunscreen based on this preliminary research.

“More extensive study is still needed,” May says. “This is just the first step.”

For instance, Ma plans to conduct electron spin resonance tests to see whether zinc oxide truly does generate free radicals, as he suspects. In addition, clinical trials will be needed before any conclusive evidence may be drawn from his studies.

In the meantime, Ma advises sunbathers to use sunscreen and to limit their exposure to the sun.

“I still would advise people to wear sunscreen,” he says. “Sunscreen is better than no protection at all.”

Besides sunscreen, zinc oxide is used in many commercial products, including plastics, paints, ointments and sealants.

Comments

  1. Nancy Uri says:

    Good job on your research!!!!!

  2. Will Foster says:

    It is the nano zinc that reacts- I would like to see the same study on non-nano zinc.

  3. Christine Spirlet says:

    Dear Dr Ma,
    Just out of curiosity, I would like to understand the relevancy:
    1) to expose human lung cells immersed in a solution containing nano-particles of zinc oxide react when exposed to different types of light for this would never happen in reality
    2) to draw conclusions about skin cancer risk from those human lung cells.
    I would very much appreciate to receive your publication(s)
    Thank you for your consideration.
    Dr Christine Spirlet

  4. Luce Myers says:

    Dear Dr. Ma,
    This is important information for those using make-up “erasers” or concealers for under eye darkness that might include zinc. Zinc is used to create an opaque quality to some cosmetics.
    Several years ago there was a Missouri S&T professor doing research regarding the use of titanium dioxide in skin applications. Are you aware of any similar testing for titanium dioxides? Thank you for your comments and research.
    Luce Myers

  5. During skin cancer awareness month this article is quite frankly VERY negligent. The study itself cites nano-particles of zinc as being the possible problem. As an advocate for consumers and all around good health, we find this news article unfortunate. The title and first paragraph would make any consumer flee from the suncreen aisle. Why not just put the information out there in a non-alarmist fashion? Zinc is one of THE healthiest forms of sun protection and does not penetrate healthy skin. Again, the reference was to nano particles. MISLEADING!

  6. Dr. Don Kilday says:

    Dr. Ma, I am in agreement with Dr Spirolet in the strange conclusion you reached based on testing with lung cells.. What relevance does it have to reality and who or what company has paid for the research..
    Look forward to any information that you could provide and very interested in your reseach.. The timing of this information is also of interest to me and many in the scientific community across the country..
    Don Kilday, Doctor of Pharmacy

  7. Joseph H says:

    Probably will..More than probably will after what i went through last summer. I’m a 49 year old white male,with medium to light skin tone. I always tan, I do get a bit of a burn that first time out but it’s mostly red, not really burnt..I have been to beaches, up the local mountaintop, sit out in the sun for lunchbreaks , ride my bicycle..But last summer i moved.the location was farther for me to bike, a bit more exposure. I have used sunscreen before and never had a problem , i also use Hawaiian Tropic oil and always get a good tan , i never exposed myself for too long..But last summer i purchased sunscreen because of my lengthier exposure , but not all that longer, and my what a burn i received . I swore it was poison ivy, a real bad rash ,with blister looking bumps..It was where ever i put the lotion..I thought it was my new apartment, i thought it was my glasses because my skin even burned underneath my transitions lenses , even after i put a flip up extra sun visor on them.. I went to my physician and she said to immediately stop using whatever it was that i was using , “it looks like rash “,she said.And refered me to a specialist for blood work that i never followed up on ..At another Dr’s office a month later they said use bacitracin”
    Yes that worked as far as relief goes , but what about before , what lotion do i use TO NOT GET BURNED”? I bought 4 different brands of sunscreen…i stopped using sunscreen and use just the oil now – i have no more burns and a very nice tan !!

  8. A. Shepard says:

    I wonder if the study could be expanded to titanium dioxide.

  9. John Miller says:

    Isn’t it interesting that the sunscreen advocates are quick to critcize the findings of this preliminary research even questioning who, or what company paid for the research. There are even complaints about this information being released. I bet they don’t question who or what company pays for the research that is pro-sunscreen use. Talk about information being released in an alarmist fashion, the CDC and other sunscreen advocates scream a the top of their lungs that if you don’t use sunscreen you’ll get skin cancer. This claim is a lie, because not everyone who is exposed to sunlight a lot and doesn’t use sunscreen gets skin cancer. I’m glad to see that someone is finally doing research into just what kind of negative effects applying all these chemicals, such as in sunscreen, has on our bodies.

  10. Very interesting…I am torn between who to believe. For sunscreen or against? Two months ago, I started to have skin rashes on my face and there was flare up almost every week. Even though blood test came in negative, the skin biopsy results were diagnosed as LUPUS ERYTHEMATOSUS. Told to wear maximum protection sunscreen with zinc oxide and titanium dioxide as sun is the trigger for this condition. I have fair skin and excellent complexion all my life till now, and can use anything on my face without any allergic reaction. I had been using Neutrogena Age Shield Face block all the time before this happens, but it does not contain zinc or titanium dioxide. So I am debating if I should switch or not in view of this new findings of zinc oxide causing cancer. To take a chance of getting skin cancer or to let this lupus develop? Either way not very nice thought…:( Hope this is NOT TRUE.

  11. Paul Saris says:

    I am in strong agreement with Dr Spirolet and Dr. Kilday on the relevance of using lung cells for such tests as well as drawing any conclusions on skin cancer based on the results.
    Targeting only the common physical sun filters this way is only geared to creating prejudice against them. It would be a completely different story if also the most commonly used chemical filters would be a part in such a comparison.
    Another issue is that Zinc oxide dissolves at pH below 6.5. The slightly acidic pH found in human tissue is actually below that number. Also Zinc oxide tends to rise the pH of an unbuffered aqueous solution to roughly 8.
    How did the study rule out that the observed was not a combined effect of UV-light on cells weakened by the toxicity of released Zinc-ions. After all, Zinc oxide is classified as a maritime pollutant with effects on e.g. daphnia.