It is fairly common knowledge that the sun has damaging effects on the skin. Anyone who has spent anytime soaking up the sun’s rays can likely tell you all about sunburns, and anyone who has ever read a newspaper or watched the evening news will likely be able to tell you that the sun is responsible for many types of skin cancer. What most of us aren’t aware of, however, are the different types of UV light and the effects that they can have on our skin.

In this article we will look at the different types of UV radiation, and how they affect us. In a world where skin cancer is now the leading cause of cancer-related deaths, understanding the sun is more important than ever.

UVA, UVB, and UVC Rays

To begin our look at the sun’s damaging rays let’s first begin with a look at the different types of UV radiation. When we generalize, without getting extremely scientific, there are three basic types of UV radiation. They can be divided into categories according to wavelength:

• UVC: 100-290nm
• UVB: 290-320nm
• UVA: 320-400nm

The two types of UV rays that have damaging effects on the skin are UVB, and UVA rays. The other type, UVC, is absorbed by the atmosphere and has no damaging effects.

UVB Rays

The most well known type of UV ray is UVB. These rays vary throughout the day, and are at their highest from 10am to 2pm. The summer months tend to be the worst for UVB damage, accounting for 70% of most people’s exposure.

UVB rays are responsible for tanning, sunburns, and in general cause the most immediately visible damage.UVB is generally considered to be the most potent and damaging type of UV light. It directly affects the epidermis (upper layer of skin), and causes damage quickly.

This is what most sunscreens protect against. In fact, that Sun Protection Factor (SPF), which is listed on your commercially bought sunscreen, directly correlates to UVB protection.

UVA Rays

The other type of UV light that causes harm is UVA. There are actually two types of UVA rays: shortwave UVA (also known as UVA II), and long-wave UVA (UVA I). The second type (UVA I) is the one that is most damaging to the skin.

Until recently UVA light was thought to have little effect on the skin. Recent studies have altered that perception.

UVA light is different than UVB in that it has some unique qualities. Firstly, it isn’t more prevalent at any time of the day. Whenever the sun is up, UVA light remains constant. It is also different in that it cannot be filtered by common glass. Window glass and automobile glass cannot stop UVA rays from passing through.

UVA has the ability to penetrate deep within the skin to affect the dermis. Its effects are more long term, and exposure to UVA light can build with time. Most sunscreens do not protect against UVA light, and until recently actually, none of them did.

Understanding the Effects of UVA and UVB Exposure

With a basic understanding of UV light, let’s begin to discuss how sunlight really affects the skin. Exposure to the sun has both short and long term effects, and understanding those dangers is the first step in being able to protect yourself.

Short-term Effects of UV Exposure

UVB light is responsible for most of the shorter term effects of sun damage. These include: sunburn, discoloration, tanning (yes a tan is damage to), and skin hyperplasia, as well as other short term effects. Too much exposure to UVB light leads to a thickening of the outer layer of skin. This is the body’s natural defense but can also cause more damage, since it also causes the epidermis to absorb and scatter more of the UVB light.

The most damaging effects of UVB light come with sunburn. Acute sunburn can lead to even more damage. The most danger occurs when the skin peels.

Peeling occurs when the body kills its cells as a last ditch effort to repair the outer layer of skin, this process is called Apoptosis. The problem is that when this occurs, under certain conditions that come with UV exposure, the body is unable to properly kill the cell. This can lead to a damaged cell that divides and turns into a tumor, and even becomes cancerous.

Some of the other short term effects of exposure to both UVB and UVA light include:

1. A reduction in  collagen production
2. An increase in free radicals which prevent normal cell function
3. Damage to enzymes  that repair DNA
4. Negative effects on your immune system as a whole.
5. Free Radical Production that causes damage to the cells, and also causes serious long term effects.

Long Term Effects of UV Exposure

The long term effects are where things begin to get even scarier. Both UVA and UVB light have long term effects.

One thing that should be noted is that exposure to UVA light builds over time. Unlike UVB exposure where the epidermis is damaged and the body then repairs it, UVA exposure adds upon itself. In other words – 5 minutes today, 1 hour in the sun tomorrow, 3 hours on the beach last Friday, and tomorrows trip to the zoo – all combine and add to the damage that has already been done.

This leads to a few common long term problems. These include free radical damage, photo-aging, and photocarcinogenisis.

Free Radical Production: One of the long term effects of UV exposure is free radical production. Free radicals are chemical particles that have at least one malfunctioning or missing electron. In the skin the most common free radicals are oxygen molecules. These tiny particles have the ability to chip away at a cell, causing it damage. After a cell is damaged the free radicals can further damage DNA and RNA that actually make the cell. Free radicals contribute to both photo-aging, and photocarcinogenesis.

Photo-Aging: UVA light is the type of ray mostly responsible for photo-aging. UVB exposure can add to this by repeatedly damaging the skin, but most UVB light is absorbed by the epidermal layer. UVA gets right under the epidermis.

Photocarcinogenesis: Both UVA and UVB light can cause skin cancer. UVB light does so by causing damage, and promoting free radicals that can alter DNA. Recent studies are beginning to show that UVA light is capable of directly altering DNA through the production of free radicals as well, which can lead to malignant tumors and even cancer.

The simple truth is that a basic understanding of UV light and the damage it can cause is the first step in protecting yourself from the negative effects of the sun.

References

Negishi, K; Higashi, S; Nakamura, T; Otsuka, C; Watanbe , M; Negishi, T. (2007) Oxidative DNA Damage Induced by 364-nm UVA Laser in Yeast Cells. Originally published by the Japanese Environmental Mutagen Society. Accessed online July 16^th 2008 from http://www.jstage.jst.go.jp/article/jemsge/28/2/74/_pdf

Brannon, Heather MD. (March 23, 2008). Effects of Sun on the Skin: Cellular Skin Changes Caused by UV Radiation. Article hosted on about.com. Accessed July 16^th, 2008 from http://dermatology.about.com/cs/beauty/a/suneffect.htm

Hugget, J. (June 28, 2005) Less Than Full Protection: Most Sunscreens Do Only Half the Job, Blocking Unsafe UVB Rays But Not Skin-Damaging UVA. Can We Get Better Cover. Washington Post. Accessed July 16^th 2008 from http://www.washingtonpost.com/wp-dyn/content/article/2005/06/27/AR2005062701099.html

Eldich, R Dr. and Various other Authors (2004) Photoprotection by Sunscreens with Topical Antioxidants and Systemic Antioxidants to Reduce Sun Exposure.  Journal of Long-Term Effects of Medical Implants. Begal House Inc. Accessed July 16^th 2008 from http://www.pacificcenterplasticsurgery.com/articles/Photoprotection-by-Sunscreens.pdf

Reinheckel, Thomas,  Bohne, Marisela,  Halangk, Walter,  Augustin, Wolfgang,  Gollnick, Harald. Evaluation of UVA-mediated oxidative damage to proteins and lipids in extracorporeal photoimmunotherapy. A Study hosted on findarticles.com Accessed July 16^th 2008 from http://findarticles.com/p/articles/mi_qa3931/is_199905/ai_n8838478

Columbia-Presbyterian Medical Center, no author listed. Two Cancer Studies: Tomatoes, Green Tea, and Cancer. Originally published in the P&S Journal: Fall 1997, Vol.17, No.3 Research Reports. Accessed July 16^th 2008 from http://cpmcnet.columbia.edu/news/journal/journal-o/archives/jour_v17n03_0009.html