Sun. The only star of the Solar system: for astronomers - G-type main-sequence star G2V, but 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. 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 - essential substances involved in the formation of bone tissue. In addition, sunlight normalizes the psychoemotional state: remember how dark the mood is on 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 burn the very life that it supports. Scientists have developed exceptional 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 the ozone layer - the primary natural filter – typically prevents it. UV-B is absorbed by the atmosphere up to 90%. However, even the remaining quantity may seriously harm living organisms. For humans, excessive radiation can cause severe skin problems: burns and a violation of the DNA structure over a long period. 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, a 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 the light sensitivity of the skin. The more you're under the sun, the more melanin your cells produce. Hereditary factors play an essential 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. At the same time, the simple busted a hump, cultivating fields whether it was heat or cold. But everything changed the other way around since World War II: pale whiteness implied the need to do 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 athletic 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 – unique chemical compounds that can reflect light or absorb it, preventing penetrating the skin. In these latter days, principles remain the same: "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: they have a pretty heavy, water-insoluble texture and cover the face with a 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, elementary 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 - para-aminobenzoic acid and its esters, salicylates, cinnamic acid derivatives (cinnamates), anthranilic esters, hydroxy benzophenones. The effect is the absorption of light energy and converting it into heat. Among holiday-makers, this easy-to-use type of product became popular very fast. It seemed that even the 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?
But the years passed, and gradually the actual value of the dark complexion, so longed for by Western people, began to emerge. By the end of the 90s of the twentieth century, cases of skin cancer had increased tenfold, and primarily among the victims were fans of long lying on the beach. Doctors were perplexed - how could it be, because the most challenging patients at one time diligently used sunscreen products, and it seems that should have reduced the risk of skin diseases such as melanoma to zero. When she began to conduct research, scientists were shocked by the findings.
Firstly, the active ingredients in the composition turned out to be far from being so harmless. For example, PABA in some cases decomposes with the formation of mutagens, and many other components are allergens. They can become a source of free radicals - initiators of oxidation, which means aging of living cells, and even cause hormonal changes.
Secondly, the designation under the abbreviation SPF - sun protection factor - invented for the convenience of consumers, as it turned out, only lulls people's attention and vigilance. The letters SPF and the numerical value 10, 30, 80 - can be seen on all packages with sunscreens. It indicates the degree of protection effectiveness. This factor shows how much this remedy slows down the appearance of the first signs of sunburn: if the bottle is labeled "SPF-30", then - in theory - you can stay in the sun thirty times longer than without protection. However, in practice, everything is much more complicated. Let's return to the types of solar radiation: we remember that C-ultraviolet is almost entirely blocked by the Earth's atmosphere, so only A and B types reach the planet's surface. In the medium-wave B-band, the radiation has more energy, and it is this radiation that, with prolonged contact with the skin, causes redness and burns. Therefore, that it was the cause of melanoma and other cancers.
However, it is now known that this ultraviolet light cannot penetrate deep into the skin, and only the upper layers of the epidermis are attacked. It serves as a kind of signal warning a person - that's it, there is enough sun for today! And we have successfully blocked this same signal system with sunscreens with protection against B-ultraviolet radiation for more than half a century. However, the real danger is fraught with radiation of the A-type. It can penetrate the deep layers of the skin and destroy the molecular structures of cells. And since the skin stopped burning, and there were no more alarm signals from the body, people began to spend long hours under the open sun, allowing lethal radiation to saturate the body.
To Sun or not to Sun?
So how to warn of all these "horrors"? The answer has been known in the past. Do not risk in vain and try not to sunbathe in the most significant solar activity clock. Wear well-ventilated clothing from natural materials (cotton, flax, silk), covering open parts of the body; Close your head using a hat with fields or visor so that the shade falls on the face. Do not skimp on good sunglasses with polarization lenses. Do not abuse "chemistry" for and from sunburn and ... Smile towards the Sun!