SUN RAYS

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Skincare is concerned with three categories of light rays ultra-violet, visible and infra-red rays. Ultra-violet or UV is divided into three sections according to their wavelengths from the sun to the earth. We are addressing the effects of UV rays on your skin, aging of your skin, why you should regulate your exposure and use sun protection.

1. UVC, shortest from the sun, usually does not reach the earth's surface being absorbed by the ozone layer above the earth. Occasionally articles are written on the ozone depletion and the possible exposure to UVC where only a brief exposure can cause light sunburn. Prolonged exposure to UVC is considered fatal.

2. UVB, long considered the "tanning ray" is strongest in northern hemisphere summer months or when parts of the earth orbit closest to the sun. When the earth orbits away from the sun in the northern hemisphere winter months it is harder to get a "suntan" because the rays can not easily reach the earth's surface. Sunblocks and sunscreens for many years only blocked the UVB ray as science was not clear on the body's reaction to UVA.

Body's Reaction to UVB

This ray only has the strength to penetrate the very top layer of your body called the epidermis which has the same thickness as a silk scarf. No blood vessels or nerve endings are present and is composed of keratinocytes (skin cells), basal cells and melanocyte cells. Melanocyte cells synthesize tyrosinase and the pigment melanin that is transferred to the keratinocytes or skin cells for color. UVB rays simulate the melanocyte cells to produce more melanin which is more color known as a suntan or if a very small area known as a freckle, brown or age spot, and chloasma, melasma or hyperpigmentation in medical terms. Sun Effects on Skin

3. UVA, was touted in the 1980's as the safe ray and sun beds were the rage. Some dermatologist backed this idea as a safe and healthy way to look your best. Since then science has found this ray actually does more damage to the body than UVB. UVA is the same strength year round it does not matter how close or how far away the sun is from the earth. The ray remains the same strength and considered a light X ray penetrating light clothing, wind shields, office windows and hats to name a few. You can test this by putting a color bound book or fabric covered furniture in a sunny window for a few months. You will start to see the color fade as the rays work on the book or furniture. Often women will say they never go out in the sun but their chest is permanently red and wrinkled, their hands look old which I usually categorize as "free-way" or "commuter" aging. A pulled down head visor in a vehicle does not protect your hands on the steering wheel or exposed chest driving into the sun. Car pooling, commuting or traveling congested areas even several times a week is enough to cause aging. When taking the train or plane is the sunlight on your hands or chest? Male skin is thicker "free-way" or "commuter" aging affects them mostly by more brown spots on the exposed side of their face. Living in a sun state or country like Mexico or equator countries provide a constant sunny environment making a daily full spectrum sunblock or sunscreen a necessity.

Body's Reaction to UVA

UVA shoots through the epidermis and disperses in the dermis the second major layer of your skin. The dermis is called the "true skin" and slows its replacement or renewing rate around the age of 28 years. Skin after this age is considered "mature skin" and damage is not mended as well if at all, fair skin people look in the mirror asking "What happened?�. These rays accelerate the aging process and like new paint on a car in a crowded parking lot years later does not look so great. The skin like paint on a car has to be taken care of and protected. The dermis is composed of collagen, elastin, blood vessels, nerve endings and ground substances (glyco-amino-glycans, mucopoly-saccharides) providing a firm youthful mattress for your skin. Prolonged exposure to UVA cracks and shrinks the collagen and elastin reducing the size of this layer allowing the epidermis (top layer) to start drooping or hanging off the body. Blood vessels become permanently dilated giving a constant red flush to the skin. The few remaining melanocyte cells that are scattered in the dermis can either die making a permanent white spot or become over active leaving a brown spot. There are no lasers or procedure available at the moment guaranteeing the removal of these brown spots and some procedures make them worse. The water binding ground substances are less and ineffective making the skin dry. In the end over exposure to this ray can put you in the dermatologist or plastic surgeon's office faster than any other aggravator. Not to mention the reported deaths from radiation poisoning from tanning beds. Be very careful and wear your sunblock or sunscreen when exposed.

Sunlight regulates our biological clock and provides essential vitamin D. Common sense should be used in regulating your amount of time in the sun.


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Ultraviolet A (UVA) radiation is now known to cause skin cancers. The first information on the way in which UVA radiation acts directly on DNA has been revealed by a CNRS team from the Laboratoire Francis Perrin (CNRS/CEA-Iramis in Saclay) in collaboration with a CEA-Inac laboratory in Grenoble. The interaction between UVA and DNA results from the collective behavior of the bases of the DNA double helix, which causes chemical lesions that can induce carcinogenic mutations. This work is published on-line on 18 March 2011 in the Journal of the American Chemical Society.

Ultraviolet A (UVA(1)) radiation represents over 95% of the solar UV radiation that reaches the Earth's surface. This UVA radiation is now known to cause skin cancers due to carcinogenic mutations brought about by chemical alterations of the four bases of DNA (adenine, cytosine, guanine and thymine). The most important chemical modification is thymine dimerization: two thymines next to each other in the DNA combine to form a new entity, known as “cyclobutane dimer”.

A CNRS team from the Laboratoire Francis Perrin (CNRS/CEA), in collaboration with researchers from the CEA Laboratoire Lésions des Acides Nucléiques, has examined the very first steps of the formation of such chemical lesions. They are publishing the first study describing the physical and chemical effects, prior to any biological effects, of UVA radiation on model DNA. The team of physical chemists examined the behavior of a synthetic DNA double helix (formed solely of adenine-thymine pairs) with regard to UVA photons. They then compared its behavior with that of two complementary single strands (containing only thymines or only adenines).

They found that DNA's capacity to absorb UVA photons results from the collective behavior of its bases. Studied individually, DNA bases (including thymine) are “transparent” to UVA. However, in this study, the scientists have shown that the absorption of UVA radiation substantially increases following the pairing of two single strands to form a double helix. In addition, the probability that a UVA photon absorbed leads to the formation of cyclobutanes is at least ten times higher in the case of a double strand than it is in the case of a single strand. These differences could be explained by changes induced by the UVA photons to the electronic structure of the bases. Following the absorption of a photon, the new electronic configuration adopted by the DNA, known as excited state, persists longer for a double strand than for complementary single strands. The thymines then have more time to undergo permanent alterations.

These experimental studies now need to be extended to more complex DNA sequences, similar to natural DNA. The stakes in terms of public health are high, especially since the quantity of UVA that reaches us is very high compared to UVB radiation (which represents less than 5% of the ultraviolet radiation that reaches the Earth's surface) and also because UVA radiation is still widely used in tanning centers.

Notes:

1 - The UV radiation spectrum is sub-divided into UVA (photons whose wavelengths lie between 400 and 315 nm (nanometers or billionth of meters)), UVB (315-280 nm) and UVC (280-100 nm). Although only part of the solar UVB radiation is filtered by the atmosphere, solar UVC radiation is completely filtered by the ozone layer of the atmosphere and thus, theoretically, does not reach the Earth's surface.

Reference:
Base Pairing Enhances Fluorescence and Favors Cyclobutane Dimer Formation Induced upon Absorption of UVA Radiation by DNA, Akos Banyasz, Ignacio Vaya, Pascale Changenet-Barret, Thomas Gustavsson, Thierry Douki and Dimitra Markovitsi – Journal of the American Chemical Society, 18 March 2011.

Contact: CNRS press officer, Tel: 01 44 96 51 51, Email: presse@cnrs-dir.fr

Source: Centre National de la Recherche Scientifique (CNRS)

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 1. http://www.911skin.com/uvbubarays.html


2. http://insciences.org/article.php?article_id=10011