Does one side of your face really age faster than the other after a few years of driving?

It's autumn now and the weather is getting colder. Compared to the scorching sun in summer, many people start to pay less attention to sun protection. In fact, sun protection is a topic that should be taken seriously all year round, especially for people who drive frequently.

The other side of the sun: it causes skin aging and even skin cancer.
Truck driver William McElligott's face was photographed by doctors at Northwestern University and published in the April 2012 issue of the New England Journal of Medicine (NEJM).

In the 15 years before this, McElligott had never noticed anything unusual about his face. It was not until his grandchildren asked about the "lump" on his face that he went to the hospital for treatment. Doctors were surprised to find that McElligott's left and right faces were like two different people. The left face of the 66-year-old man was covered with wrinkles that formed deep lines and appeared sunken and sagging. His right face was tighter and looked much younger.

Image source: The New England Journal of Medicine

For decades, McElligott has been driving a truck in Chicago, USA, delivering milk to residents in the community. He drives on the left side of his face, so this side is exposed to the sun for a long time, while the other side is spared. Doctors believe that long-term exposure to ultraviolet (UV) rays has caused photoaging on the left side of his face.

Through the glass

We sometimes say that sunbathing makes us feel good, and UV radiation also helps the body produce an important nutrient, vitamin D. But overexposure can cause sunburn, premature skin aging and even skin cancer.
If arranged from long to short wavelength, ultraviolet rays can be divided into UVA (315-399 nanometers), UVB (280-314 nanometers) and UVC (100-279 nanometers). However, all UVC and most UVB are absorbed by the earth's ozone layer, so almost all the ultraviolet radiation received by the earth is UVA.

Ultraviolet light. Image credit: NASA

The harm of UVA was discovered relatively late. It was not until 1969 that American dermatologist Albert Kligman discovered the photoaging effect of UVA on the skin. This was nearly a century later than UVB. The shorter the wavelength, the stronger the radiation. Therefore, doctors discovered as early as the 19th century that UVB can cause skin burns, and long-term exposure can also cause skin cancer.

In contrast, the effects of UVA on the skin are less immediate and accumulate over time. In a sense, this makes UVA more harmful. What’s more, UVA is more penetrating than UVB—UVA can pass through glass, such as car windows, and then penetrate the epidermis of the skin, and may even reach the upper dermis, where it can react with any substance in the skin, including proteins, DNA and lipids. Doctors believe this is what McElligott has been suffering from on the left side of his face for a long time.

If the damage is allowed to continue, UVA may also induce a large number of DNA mutations, eventually causing skin cancer. Therefore, doctors recommended that McElligott use topical retinoids and sun protection products including sunscreen.

Are you wearing enough sunscreen?

We are all familiar with sun protection, but statistics from many regulatory agencies show that we are not doing enough - of course, this excludes those beauty-conscious people who wrap themselves in sun-protective clothing and hats in the summer.

According to the U.S. Food and Drug Administration (FDA), we should apply sufficient sunscreen to the entire face (except the eyes) and body areas, especially those areas that are often overlooked, including the ears, nose, mouth, hands, the edges of the hairline, and areas of the head that are exposed due to baldness or thinning hair.

However, the FDA found through research in 2019 that four active ingredients in sunscreen - avobenzone, oxybenzone, octocrylene and ecamsule - are absorbed into the blood and the concentration exceeds the threshold that the FDA considers safe and no longer requires more safety data.

Therefore, the FDA judged that these active ingredients need further testing to obtain more safety data so that the FDA can determine what level of absorption is safe. But in the meantime, the FDA's press release emphasized that "absorption does not equal danger, so it is recommended to continue to use sunscreen."

In fact, more than 20 years ago, scientists discovered that sunscreen (mainly oxybenzone) was present in human urine, and expected that this came from sunscreen in the blood. But oxybenzone has not been found to have any long-term harmful effects since it was used in sunscreens in the United States in the 1980s. However, the FDA did not list these active ingredients as safe, but said that more data is still needed to prove their safety.

Image source: pixabay

It is worth mentioning that these are all chemical sunscreens (active ingredients are organic substances connected by many carbon atoms), and the only ones classified as safe by the FDA are physical sunscreens, including zinc oxide and titanium dioxide nanoparticles. Existing studies have shown that zinc oxide and titanium dioxide nanoparticles used in sunscreens will hardly penetrate the skin, but spray-type sunscreen products may cause particles to be inhaled and affect the lungs.

This physics is not that physics

The FDA once believed that nanoparticles like zinc oxide could only provide sun protection by reflecting and scattering light, which was equivalent to a physical barrier, and therefore called them "physical sunscreens" in 1978. However, many subsequent studies have found that zinc oxide and titanium dioxide nanoparticles have a certain optical band gap and can directly absorb ultraviolet rays, and then according to the law of conservation of energy, convert it into other energy forms such as heat, just like chemical sunscreens.

Although the FDA revised the definition and mechanism of action of physical sunscreens in its 1999 report version, the statement that "it is just a physical barrier that only reflects and scatters" is deeply rooted and has not completely disappeared today.
Don’t forget to wear sunscreen on cloudy days, after all, up to 80% of ultraviolet rays can pass through clouds.

References

[1]https://www.nejm.org/doi/full/10.1056/NEJMicm1104059?logout=true

[2] https://www.cdc.gov/nceh/radiation/ultraviolet.htm

[3] https://onlinelibrary.wiley.com/doi/10.1111/jocd.14004

[4]https://labmuffin.com/fact-check-feature-why-you-should-protect-yourself-from-uva/

[5]https://www.fda.gov/drugs/understanding-over-counter-medicines/sunscreen-how-help-protect-your-skin-sun

[6] https://jamanetwork.com/journals/jama/fullarticle/2733085

[7] https://www.fda.gov/news-events/fda-voices/shedding-more-light-sunscreen-absorption

[8] https://doi.org/10.1016/S0140-6736(05)62032-6

[9]https://labmuffin.com/more-sunscreens-in-your-blood-the-new-fda-study/

[10]https://www.researchgate.net/publication/282495157_Physical_sunscreens

Planning and production

Source: Global Science

Editor: Bai Li