About this Article
Written by: Hieu Nguyen
Written on: May 4th, 2010
Tags: biomedical engineering, health & medicine, lifestyle
Thumbnail by: Jambunathan/SXC
About the Author
In Fall 2010, Hieu Nguyen was a junior studying Electrical Engineering at the University of Southern California. After receiving his B.S. degree, he hopes to continue his education in graduate school in pursuit of a challenging engineering career. Hailing from Hawaii, he enjoys riding the ocean’s waves and basking in sunny, tropical climates.
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Volume XI Issue III > Rubbing It In: Modern Sun Protection
Sun damage is a cumulative process, meaning that every moment of exposure has a long-term impact. Overexposure to the sun’s harmful ultraviolet (UV) radiation can cause burns, diseases, and cancers—substantially contributing to mortality rates in fair-skinned populations. The severity of skin cancer is real; there are more new cases of skin cancer than the combined figures for lung, breast, prostate, and colon cancers each year. Helping to protect against sunburn and skin cancer, sunscreen is a topical product that absorbs or reflects the sun’s UV light. It is important to consider the global impact of sunscreens and the scientific and engineering principles of this skin-care product. There have been recent advances in photoprotection, including the development of broad-spectrum sunscreen and the sun protection factor. Although sunscreens have been in use for over 70 years, their health applications are still being explored.


Our sun—the most powerful entity in our corner of the universe—is dangerous. Almost everyone comes into contact with its rays every day. Whether you are walking your dog around the block or watching a 3-hour college football game in the stands at a stadium, your skin is at risk. It is well-known that solar radiation is harmful; you have probably taken a few precautions in the past to protect yourself from the sun’s intensity by wearing brimmed hats, polarized sunglasses, or high-SPF sunscreens (see Fig. 1). For many, lathering on sunscreen lotion may seem like a chore. But what exactly are you “applying liberally” to your body? How much protection does sunscreen really have to offer against sunburn and skin cancer, and how long will these safeguards last? The answers to these questions can be found by considering the scientific and engineering principles behind the $1.9 billion industry skin-care product: sunscreen.

A Harmful Sun

Natural sunlight contains, among other things, ultraviolet photon particles of light. These photons are shorter in wavelength and contain more energy than visible light, giving them the ability to cause DNA damage in skin cells. Ultraviolet radiation is broken down into the following three types of wavelengths:
Stilfehler/Wikimedia​ Commons
Figure 1: Commercial bottle of high-SPF sunscreen.
  • Ultraviolet, Type A (UVA)
  • Ultraviolet, Type B (UVB)
  • Ultraviolet, Type C (UVC)
On the Earth’s surface, we are exposed to UVA (wavelength 315-400 nm) and UVB (280-315 nm) photons; the UVC (100-280 nm) rays are completely absorbed by the atmosphere and never reach us. The longer wavelength UVA rays cause tanning and penetrate the deeper layers of skin, while the shorter wavelength UVB rays damage DNA and are the primary cause of sunburn and skin cancer. Since UV radiation falls outside of the visible light spectrum (rays between wavelength 400-700 nm), the human eye cannot perceive UV rays. Humans are also unable to feel UV radiation, leaving the body vulnerable with no mechanism to warn itself against overexposure.

The Sun’s Effects on Our Skin

Our skin is highly susceptible to critical damage from the sun’s ultraviolet rays; any exposure to UVA or UVB light can alter or damage it. Without protection, long-term exposure to natural sunlight inflicts damage on the skin cells, causing them to tan, burn, and peel.
Although a suntan is often considered an “emblem of good health,” tanning for its own sake has no health benefit and is actually a health hazard [1]. Tanning is your skin’s defense mechanism against the sun, and any change to your natural skin color is a sign of skin damage. When your skin is exposed to moderate levels of radiation, a chemical reaction in its cell system occurs. Your skin protects its complex structure of sensitive cells by producing a brownish pigment, called melanin, which absorbs and reflects UV rays, dissipating the energy as harmless heat. This is one of the reasons you heat up in the sun. Special pigment-producing cells called melanocytes manufacture these color capsules and send them to the surface of your skin, causing a “tanned” skin tone.