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Why does skin become leathery after too much UV light from sun exposure?

The long-held notion that prolonged sun exposure can toughen human skin is more than just an observation. It’s a physical alteration that has intrigued people for centuries. Overexposure to UV light is evident in the “leathery” complexions of farmers, road crews, sunbathers, and those who frequent tanning booths. However, the biological explanation for this phenomenon has remained somewhat elusive until now.

Researchers from Binghamton University have delved into the mystery of sun-induced skin toughening, unveiling how ultraviolet (UV) radiation alters the microstructure of the skin.

Their recent study, published in the Journal of the Mechanical Behavior of Biomedical Materials, particularly emphasizes the effects on collagen, a critical fibrous protein that holds together tissue, tendon, cartilage, and bone in our bodies.

Binghamton University Associate Professor of Biomedical Engineering Guy German led the research. He explained the significance.

“We don’t want to put a fear factor in here saying ‘don’t go out in the sun,’” he said. “But extended periods of time under UV light can toughen up your skin as well as lead to a higher risk of carcinogenic problems.”

German collaborated with PhD student Abraham Ittycheri, Zachary Lipsky, PhD ’21, and Assistant Professor Tracy Hookway at the Thomas J. Watson College of Engineering and Applied Science’s Department of Biomedical Engineering for this study.

Studying UV light and sun exposure

Building on earlier research that German and Lipsky conducted on the skin’s outer stratum corneum, the team compared full-thickness skin samples before and after exposure to varying levels of UV light.

The methodology involved conducting a mechanical stretch test on skin samples. “One way to characterize the material characteristics of skin is by conducting a mechanical stretch test on it,” Ittycheri explained.

“If it stretches very easily, it’s relatively compliant, but if it’s much harder to stretch it, you can characterize it as much stiffer. My experiment was to see what the isolated effects of UV light would be and compare it with a scenario where a skin is not exposed to UV light.”

UV light changes collagen fibers

The findings were revealing. The researchers observed that as the skin absorbed more UV radiation, the collagen fibers became more tightly packed. The result was increased stiffness and harder-to-break tissue.

German identified correlations with the cross-linkage theory of aging. It suggests that the accumulation of undesirable molecular bonds over time could cause cellular dysfunction.

Assistant Professor Tracy Hookway found similarities between how heart and skin cells respond to damage. “Our body has this natural response in any tissue when there’s some sort of injury, which likely happens in the stratum corneum,” Hookway noted.

She went on to compare the process to what happens in the heart after a myocardial infarction. After a heart attack a scar is built, and the heart’s function is altered.

Hookway also warned that the body’s reaction, although life-saving at times, might not always yield good results. This biological intervention could lead to other medical issues down the line. Understanding the mechanics of these reactions might enable future physicians to guide the reactions towards healthier outcomes.

Implications for human health and wellness

The study’s implications stretch beyond mere biological interest. As Ittycheri pointed out, the skin’s function is paramount to human health and well-being.

“Any kind of disruption to the normal process of skin is going to be extremely dangerous and detrimental to our overall lifestyle,” he said. “That’s not even going into the cosmetic side of things, where a person’s perception about themselves can be challenged when their skin does not look good.”

The Binghamton University team has not only provided vital insights into a longstanding question but also opened doors for further collaboration and research. The study’s findings could contribute to new approaches to maintaining and even strengthening the skin.

The skin is our body’s largest organ and first line of defense against environmental threats and must be protected. The potential implications for both health and aesthetics make this research a significant stride in understanding and ultimately harnessing the skin’s response to the sun.

More about ultraviolet light

Ultraviolet (UV) light is a form of electromagnetic radiation that lies between visible light and X-rays in the electromagnetic spectrum. It has wavelengths ranging from 10 to 400 nanometers (nm), shorter than visible light but longer than X-rays.

UV light plays a crucial role in various natural processes and human activities but also has potential hazards.

Classification of UV Light

Ultraviolet light is typically classified into three categories:

UV-A (320-400 nm)

This type accounts for approximately 95% of the UV radiation that reaches the Earth’s surface. It can penetrate deeper layers of skin and is responsible for skin aging and some skin cancers.

UV-B (280-320 nm)

The Earth’s atmosphere partially absorbs UV-B, which represents about 5% of UV radiation.It affects the outer skin layers and leads to sunburn and other skin damage.

UV-C (100-280 nm)

The atmosphere completely absorbs UV-C rays, preventing them from reaching the Earth’s surface. They often use these highly destructive rays in germicidal applications.

Sources of UV Light

Natural Sources

  • The Sun: The primary natural source of UV light, the Sun emits all three types of UV rays. However, only UV-A and some UV-B reach the Earth’s surface.
  • Black Lights: Certain types of minerals emit UV light when illuminated by specific wavelengths of visible or ultraviolet light.

Artificial Sources

  • UV Lamps: Used in various applications like water purification, medical treatment, and food sterilization.
  • Tanning Beds: These use UV-A and UV-B lamps to produce a cosmetic tan.


Health and Medicine

  • Vitamin D Production: UV-B rays stimulate the production of vitamin D in the skin, essential for bone health.
  • Phototherapy: Medical professionals use UV-B rays to treat skin conditions such as psoriasis and eczema.
  • Sterilization: Manufacturers use UV-C lamps to sterilize air, water, and medical equipment.

Industrial Applications of UV light

  • Water Purification: UV-C rays destroy bacteria and viruses in water, making it suitable for drinking.
  • Inspection Processes: UV light reveals flaws in various materials, aiding in quality control.

Environmental Studies

  • Weather Forecasting: UV measurements contribute to meteorological predictions.
  • Climate Studies: UV radiation affects the Earth’s climate, and monitoring UV levels assists in understanding climate change.

Health Risks of UV light

  • Skin Cancer: Prolonged exposure to UV-A and UV-B can lead to various types of skin cancer.
  • Eye Damage: UV rays can cause cataracts and other eye issues.
  • Premature Aging: UV-A rays can lead to premature aging of the skin.

Safety Measures

  • Sunscreen: Sunscreens containing UV filters protect the skin from harmful UV rays.
  • Protective Clothing: Wearing protective clothing and sunglasses shields the skin and eyes from UV radiation.
  • Avoiding Peak Hours: Limiting sun exposure during peak UV radiation hours reduces risk

Ultraviolet light is an essential yet potentially hazardous part of our environment. Its broad range of applications in medicine, industry, and environmental science highlights its importance. However, awareness of its risks and adherence to safety measures is vital for human health.

Whether harnessed for beneficial purposes or mitigated to prevent harm, UV light remains a fundamental aspect of our world, requiring careful understanding and management.

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