Sun. The only star of Solar system: for astronomers - G-type main-sequence star G2V, but for all creatures on Earth - a source of light and warmth. Indeed, life on the planet in its present form would be impossible without solar energy, in fact, it runs the processes of photosynthesis - the formation of organic compounds with the oxygen release.
This type of electromagnetic emanation is called ultraviolet. It has great importance for health and human life: UV has antiseptic properties, in moderate amounts it stimulates the immune system. Also, it’s used to treat many skin diseases such as psoriasis, eczema, tetter. Ultraviolet synthesized vitamin D3 - important substances involved in the formation of bone tissue. In addition, sunlight normalizes psychoemotional state: remember how dark the mood is in gray and dull winter days and how the body enjoys the first stream of light in spring.
But it’s not all that simple and "sunny." The overflow of UV radiance can literally burn the very life that it supports. Scientists have developed special standards ISO which determines the types of solar emission:
- long-wave range, or ultraviolet A
- medium-wave range, or ultraviolet B
- short-wave range, or ultraviolet C
UV-C type radiation can’t reach the earth's surface, because ozone layer - main natural filter – normally prevents it. UV-B absorbed by the atmosphere up to 90%, however, even the remaining quantity may seriously harm living organisms. For humans, excessive radiation can cause serious skin problems: burns, and over a long period – a violation of the DNA structure. An excess of ultraviolet radiation can destroy nucleic acids, which make up our genetic code. It’s leading to genetic mutations, and as a consequence - to cancer. Skin is the first and most important protective barrier for ultraviolet radiation in the human body. The main element of this system is melanin, kind of dark pigment. It absorbs light in the upper layer of the skin - the epidermis, without passing radiation into the deeper layers and thereby protects the whole body. This "smart" substance produced by the human body and its amount determines light sensitivity of the skin. The more you’re under the sun, the more melanin your cells produce. Hereditary factors play an important role here: fair-skinned Westerns have much less melanin in the skin than, for example, native inhabitants of Africa, and therefore they burn much faster. Do not forget about the view: bright sunlight with prolonged exposure adversely affects the state of the eye cornea and retina and can cause severe burns or even blindness.
Until the middle of the last century, milky skin was a privilege of the aristocracy spending their leisure time on the shady lawns of family estates, while the simple busted a hump, cultivating fields whether was heat or cold. But everything changed the other way around since the World War II: pale whiteness implied the need to make their backbreaking daily work in factories and offices, and chic bronze tan was associated with the bliss of tropical resorts. A bandwagon to be a "chocolate" had begun. Images of brawny macho in an embrace with sporty babes, sipping cocktails on golden beaches, flooded TV screens and slick magazines.
Chemistry: dubious help
However, Mother Nature takes its course, and fair-skinned Caucasians instead of the desired "bronze" skin received painful burns and the effect of "snakeskin" which peeling rags. The cosmetic industry helped out. The UV filters were invented – special chemical compounds that can reflect light or absorb it, preventing penetrating into the skin. In these latter days, principles remain the same: there are "natural" and "chemical" UV filters. Reflecting filters scatter UV and consist of mineral pigments - titanium dioxide, zinc oxide, magnesium silicate. These compounds do not react with the skin, however, there are certain disadvantages to use: they have quite heavy, water-insoluble texture and cover the face with the dense whitish film. If you've ever spent a vacation in the hot countries where there are some spots for surfing, you have probably seen brave guys with surfboards and motley "war paint" on their faces - a zinc-containing cream. Spending on the water for a few hours under the merciless tropical sun, surfers think much about the health of their skin.
Chemical UV filters are transparent, readily water-soluble substances, very easy to add to the wide variety of cosmetics such as sunscreen creams and lotions, day creams, powder, toners, lipstick and lip gloss. In the structure, these cosmetics may comprise PABA - p-aminobenzoic acid and its esters, salicylates, cinnamic acid derivatives (cinnamates), anthranilic esters, hydroxybenzophenones. The effect is the absorption of light energy and converting it into heat. Among holiday-makers, this easy-to-use type of products became popular very fast. It seemed that even equatorial sun was powerless. Using these creams still made it possible to get a tan, skin just darkened slowly and gradually, not covered with painful flash burns.
Beauty… to death?
Years went by, and gradually the true cost of so highly-rated swarthiness was brought to light. Cases of skin cancer increased several-fold By the end of the 90s of the twentieth century, especially among the fans of the long-lye on the beach. Doctors were puzzled – how come? The most serious patients assiduously used sunblocks, and it had to bring a risk of skin diseases such as melanoma to naught. When scientists began to conduct the researches they were astonished at shocking facts. Firstly, the active ingredients in the composition were not so benign. For example, the aforementioned PABA sometimes decomposes with mutagens, many other components are allergens and can be a source of free radicals initiating oxidation, therefore, the cell aging, and even cause hormone disruption.
Recently, in the US an important study was conducted among several thousand volunteers who regularly use sun protectors. According to the results, scientists have found that UV filters can be absorbed into the bloodstream and accumulate in the body. In particular, benzophenone-3 (oxybenzone), popular among manufacturers of "solar" cosmetics UV filter, was detected in 96% of the investigated urine samples taken from Americans of different ethnic origin, age and sex. Thus for young women, the average content of this material was three times higher than for men. Take a tube of your favorite and familiar sunscreen, and carefully read its ingredients on the label. Are you sure to "feed" your body all this chemistry for the sake of dubious fashion?
Secondly, well-known designation SPF (sun protection factor), invented for the customer convenience, as it turned out only lull the alertness and attention. SPF with numerical value - SPF-10, 30, 80, etc. - can be seen on all sunscreens, meaning the degree of protection. This factor indicates how this particular product slows down the appearance of the first signs of sunburn, if there is an inscription on the bottle «SPF-30», theoretically you can stay under the sun thirty times longer than without any protection. However, in reality, everything is much more complicated. Let's get back to the types of solar radiation: we remember that UV-C is almost completely blocked by the Earth's atmosphere, so only A and B type reach the planetary surface. The medium-wave range radiation has more energy, and that if it has prolonged contact with the skin it can cause redness and burns. Therefore, it was widely thought that UV-B was the cause of melanoma and other cancers. Now it is known that Ultraviolet B emission is not able to penetrate deep into the skin and are exposed to attack only the upper layers of the epidermis. It serves as a kind of signal, warning people – enough sun for today! This particular signaling system we successfully blocked for over half a century with sunscreen protection against ultraviolet B. The real danger is in radiation-A type, it is able to penetrate into the deeper layers of the skin and destroy the molecular structure inside the cells. Since the skin has ceased to be burnt, and alarm signals from the body are no longer received, people began to be carried out under the open sun for hours, allowing deadly rays to infiltrate the body.
To sun or not to sun?
So how can we prevent all these unpleasant things? Even our great-great-grandmothers knew the answer. Do not risk in vain, remember that better a little sun to warm us than a big one to burn us. Try not to sunbathe during the solar activity rush hours; wear light, well-ventilated clothes made from natural materials (cotton, linen, silk) covering the exposed parts of the body; close your head and face with sunhats; be lavish with good polarized sunglasses; do not abuse the chemical sunblocks... and smile towards the Sun!