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Sunscreen ingredient zinc oxide may cause skin cancer in some users

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By Jimmy Downs

Monday May 27, 2013 (foodconsumer.org) -- Sunscreens are intended to prevent the skin from being damaged by UV rays, which are known to increase the risk of skin cancer.   A study in Biomaterials suggests that zinc-oxide based sunscreen products may actually cause DNA damage in the skin and induce skin cancer in some people who lack the capability of naturally preventing cancer.

The study led by K. W. Ng and colleagues from School of Materials Science and Engineering, Nanyang Technological University in Singapore found a large number of BJ cells (skin fibroblasts) died after they were treated with zinc oxide nanoparticles, indicating that the nanoparticles can cause damage to the cells and or DNA and trigger the cells to commit suicide through apoptosis after they found the damage too excessive to be repaired. 

The damage induced by zinc oxide is evident because not only many cells died, but also at the same time, p53, the most critical tumor suppressive protein, was activated after the exposure to zinc oxide nanoparticles, which are commonly used in sunscreens.  The activation of p53 indicates that the cells found a self-defense pathway justified to prevent against carcinogenesis induced by zinc oxide nanoparticles.

Programmed cell deaths (apoptosis) are a protective measure found in healthy cells, to kill injured cells which would not be repaired otherwise, and prevent the carcinogenesis of the injured cells.  Because no repair is perfect and potentially leaves damage un-repaired leading to mutagenesis and carcinogene eventually. This means, even in people with healthy levels of p53, cellular and or DNA damage induced by zinc oxide may increase the risk for skin cancer.

The study also shows that cells with p53 knocked out after exposure to zinc oxide nanoparticles actually increased DNA damage and cell progression, which is bad.  This means that the outcome of the cellular or DNA (prior research has found nanoparticles can enter cells and cause DNA damage) can be the carcinogenesis in individuals who have a deficiency of p53 and are unable to have a normal response to the DNA or cellular damage induced by zinc oxide nanoparticles.

Nanoparticles like zinc oxide and titanium dioxide used in sunscreens can not only directly disrupt DNA after entering cells, but also damage DNA by absorbing UV radiation, triggering photocatalysis and releasing harmful reactive oxygen species, according to an Australasian Journal of Dermatology report authored by D.T. Tran and R. Salmon from Illawarra Dermatology and Laser Clinic in Wollongong in New South Wales Australia.

In summary, zinc oxide nanoparticles commonly used in sunscreen products and also dietary supplements may damage the skin causing cell deaths and potentially leading to the cancer development in some individuals.  Indian scientists have reported in the journal Apoptosis that ingested zinc oxide nanoparticles can damage the liver cells.

The best way to prevent skin cancer from UV exposure is to avoid over-exposure to UV rays during the hottest hours of the day.  If you cannot avoid it, make sure to wear a hat and heavy cloth to protect your skin from being over-irradiated by UV rays from the sun.  Keep it in mind that some exposure to the sun is the way for humans to get vitamin D and no one should try to completely avoid the sun exposure, which can cause vitamin D deficiency leading to the development of many chronic diseases including lethal skin cancer.

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