We are looking forward to the summer to soak up the sun, and then flaunt a beautiful tan in front of friends and colleagues. However, how many people know what natural forces are involved in the pleasant bronze darkening under the rays of the sun? Tanning is the body’s response to sunlight, more precisely, a protective reaction to ultraviolet radiation, the most dangerous part of solar radiation. In response to ultraviolet radiation, melanocytes (cells of the epidermis) produce the pigment melanin. Its main function is the absorption of ultraviolet light. The number of melanocytes in people of different nations, from the lightest-skinned Europeans to the blackest Africans, is about the same. The difference is that the skin of Europeans produces melanin only under the influence of ultraviolet radiation, while people of other races produce it continuously, so their skin is always pigmented to some extent. If the skin of a European is not tanned, its cells are not protected from ultraviolet radiation. Therefore, the probability of getting burned and getting sunburn is high. Usually, sunburn from excessive exposure to the sun is painful redness of the skin (first degree burn) or even blisters (second degree burn).

The spectrum of solar radiation is quite wide — from radio waves to gamma radiation. However, not all ranges reach the Earth’s surface. Radio waves and the infrared range are not of interest to us in the context of this topic, gamma and X-ray radiation, fortunately, are absorbed by the atmosphere (otherwise, at least some living beings would hardly have survived on Earth). In this case, we are interested in the so-called atmospheric transparency window in the visible part of the spectrum and the adjacent infrared (IR) and ultraviolet (UV) ranges. It’s worth talking about the latter in detail, since it is responsible for darkening the skin, that is, tanning. The spectrum of solar ultraviolet (UV) is conventionally divided into three ranges. First, it is the long-wavelength part of the near ultraviolet (from 315 to 400 nm). The waves of this range, which is commonly called UV-A for short, make up a significant part of the solar ultraviolet and generate a tan that protects our body from burns. Sometimes this range is also called “black light” or “Wood’s light” (after the American physicist Robert Wood). — it is invisible to the human eye, but under its influence, many substances begin to glow (fluoresce) in the visible range. This property is actively used in criminology to detect traces of various substances, as well as to protect letterheads of securities and banknotes (almost every cash register has a UV lamp). The second part of the solar ultraviolet is medium UV, or UV-B. Radiation with wavelengths of 280-315 nm is responsible for the fact that we get sunburns. If the skin is not tanned, its cells are not protected from ultraviolet radiation. Therefore, the probability of getting sunburned and sunburned is especially high in the first days of vacation. The third part is the short—wavelength part of the UV range, or UV-C, the harshest radiation with wavelengths from 100 to 280 nm. UV radiation with wavelengths less than 200 nm is called vacuum ultraviolet, because it can only propagate in a vacuum and is completely absorbed by gases that make up the Earth’s atmosphere. Therefore, the UV-C range, fortunately, practically does not reach the Earth’s surface. Fortunately, because this radiation is dangerous for living beings (it is absorbed by DNA molecules and destroys them). However, there is a silver lining — UV-C lamps are actively used in industry and medicine as an effective and safe means of disinfection of air, water, etc.

In the 20th century, tanned skin became a hallmark of the elite, and bronze was considered a sign of youth, strength, and an active lifestyle. In addition to the purely aesthetic effect, a tan completely erases all traces of fatigue from the face, removes pallor and gives the owner of chocolate-colored skin a cheerful appearance. Scientific data also contributed to this. Indeed, hundreds of experiments have convincingly proved that UV radiation with a wavelength of 290-400 nm increases the tone of the sympathetic-adrenalin system, activates protective mechanisms, and increases the secretion of a number of hormones. Under the influence of UV, histamine and similar substances are formed that have a vasodilating effect and increase the permeability of skin vessels, improve carbohydrate and protein metabolism in the body, increase pulmonary ventilation, increase gas exchange, oxygen consumption, and activate the activity of the endocrine system. Under the influence of UV rays, the content of antibodies in the blood increases significantly, which increases immunity— the body’s resistance to infectious and viral diseases. In winter and spring, when the body’s protective functions are weakened, UV rays help fight colds. At the beginning of the twentieth century, doctors were surprised to realize that it was important not only to eat right, but also to expose themselves to the sun’s rays.

Under the influence of sunlight, an anti-rickety factor called vitamin D is formed in the skin. Vitamin D is vital for the human body. It regulates the blood levels and absorption of the minerals calcium and phosphorus, as well as their intake into bone tissue and teeth. Together with vitamin A, it protects the body from colds, helps prevent tooth decay and gum diseases, helps fight rickets (bone curvature), osteoporosis and accelerates the healing of fractures. The source of this vitamin is butter, cheese and other dairy products, egg yolk, fish oil, caviar. They contain vitamin D not only in animals, but also in plant products: alfalfa, horsetail, nettle, parsley, mushrooms. But even with proper and sufficient nutrition without sunlight, vitamin D is not produced in sufficient quantities. Today it is known that vitamin D is a group of biologically active substances consisting of pherols that are activated by ultraviolet radiation (these include ergocalciferol and cholecalciferol). In the body, this process takes place in the skin. The skin is the largest human organ. Its weight ranges from 2.5 to 5 kg, and its area is 1.5−2 m2. Each square centimeter of skin contains on average three blood vessels with a total length of about 40 cm, 9300 melanocytes (pigment cells) and about 1,000 sweat glands. The skin got the function of interacting with the outside world, so it has a complex structure and is filled with “sensors” and “protective devices”. To maintain the necessary vitamin D levels in the body, it is enough to expose your hands and face to the sun 2-3 times a week for 10-15 minutes. And for the proper development of a child, about 20 minutes of sunlight is necessary. It has been found that more than half of bone fractures in the elderly can be prevented by taking vitamin D or by consuming more milk and dairy products and sunbathing. Sunbathing also helps with muscle pain, arthritis, and rheumatic conditions. Based on these facts, scientists have concluded that an intense tan can be considered a panacea and an indicator of good health.

However, it is important to observe moderation in everything. As the ancient Aesculapians noted, the most remarkable miraculous medicine in an excessive dose turns into a deadly poison. Despite the obvious advantages, the sun and ultraviolet are not as harmless as they seem at first glance. If you get carried away with tanning, you can grow old much earlier than programmed by nature. The basement membrane of the epidermis has a limited resource for the reproduction of new skin cells. Frequent burns caused by UV-B wear it down, and the layers of the epidermis lose their regularity. The dermis becomes thinner and loses collagen and elastic fibers. Substances and tissues that create the effect of skin elasticity disintegrate, wrinkles appear. Under the influence of ultraviolet radiation, premature skin aging occurs, which is called photoaging. It has long been noticed that women living in the south age noticeably faster than those living in the middle zone and further north. If you compare a forty-year-old Southerner who is constantly exposed to the strong sun and a resident of Northern Europe who avoids excessive solar radiation, their skin is strikingly different, and women often look like mother and daughter. This happens precisely due to photoaging. Wrinkles appear in women earlier than in men, since the thickness of women’s skin is two thirds of the thickness of men’s. The thinner a woman’s skin is, the sooner she will show signs of aging and wrinkles. It is also noted that brunettes are less susceptible to ultraviolet rays, and blondes burn much faster. Women are most susceptible to sunburn during pregnancy, so they need to dose their tan more carefully. The skin consists of three easily distinguishable layers: the thin epidermis, dermis, and subcutaneous fat (hypodermis) The epidermis is the most active and complex part of the skin — the thin epidermis is 0.25 mm thick (only on the palms and feet it is noticeably thicker). This is the outer protective shell of the skin. The dermis is the middle, thicker and more durable layer of the skin, which is based on connective tissue. The dermis consists of two layers. The outer papillary layer contains loops of capillaries in the outgrowths, feeding the basal layer of the epidermis, and nerve endings. The deep reticular layer of the dermis contains blood and lymph vessels, nerve endings, hair follicles, glands, as well as elastin, collagen, and smooth muscle fibers that give the skin strength and elasticity. Subcutaneous fat — the last layer of the skin consists of individual fibers and bundles of connective tissue and fatty accumulations penetrated by blood vessels and nerve fibers. The function of adipose tissue is to store a reserve of nutrients. In addition, it serves for thermoregulation and protection of internal organs.

But the biggest danger that arises from exposure to excess UV-B radiation is damage to the DNA of melanocytes. It leads to melanoma (skin cancer). Therefore, the recommendations of modern medicine are as follows: small doses of ultraviolet radiation, leading to minor damage, stimulate skin activity and benefit the body, and large doses can destroy skin cells. Special sunscreens (usually based on titanium dioxide) have been created to block or absorb unwanted ultraviolet rays. Their effectiveness is characterized by the numerical indicator SPF (Sun Protection Factor) indicated on the label. This number shows how many times the intensity of UV radiation that reaches your skin is weakened, and, accordingly, how many times longer you can stay in the sun without the risk of burns. When choosing creams, you should also take into account that different people react differently to sunburn. For some, even a ten-minute exposure to the sun causes burns and redness. In Europe, four types of human skin are distinguished by sensitivity — from “Celtic” to “Mediterranean”. Is it possible to avoid danger if you do not use natural solar radiation, but sunbathe in tanning salons? After all, the spectrum of artificial sources of ultraviolet radiation is limited to the range of UV-A, and UV-B (and even more so UV-C) is absent. However, experts from the World Health Organization (WHO), meanwhile, consider tanning beds to be the most significant risk factors for cancer. This category also includes such carcinogens as cigarettes, arsenic, asbestos, mustard gas, etc. Unfortunately, contrary to the opinion about the harmlessness of UV-A radiation, recent animal experiments show the insecurity of all three UV ranges (A, B and C). Therefore, WHO recommends against using tanning devices for cosmetic purposes, and some American medical associations recommend using self-tanning creams instead of sunburn and tanning beds.

Our skin is constantly being renewed. The outer stratum corneum of the scales of the dead epidermis is rejected, and it is replaced by the underlying one. The body completely replaces dead skin cells with new ones in about four weeks. This amounts to about 1,000 skin changes over the course of a lifetime, and by the age of 70, people lose about 50 kg of epidermis. According to forensic laboratory studies, approximately 70% of the dust in your house is dead skin cells of your family members, their friends and other people who have visited this dwelling. And even a tiny particle of dandruff contains a complete DNA record that tells you who you are genetically. In other words, it is almost impossible to visit anywhere without a trace: your “personal genetic business card”, which is much more detailed and accurate than a fingerprint, will certainly remain a documentary evidence of this.

Before the industrial revolution of the 19th and 20th centuries, pale skin was in fashion, which was considered a hallmark of the aristocracy. And the tan indicated that a person spends a lot of time outdoors, doing hard physical labor. Then the living conditions changed radically, and everything turned upside down: factory workers and employees began to spend most of their time indoors, and tanning became the object of envy, as evidence of a large amount of free time and a sporty lifestyle. However, in recent years, everything has been changing again: tanning is gradually going out of fashion. According to American researchers, 67% of women and 46% of men claim that they try not to go out into the sun once more, so as not to expose themselves to excessive UV radiation. Perhaps there are fewer cautious men, because they are more likely than women to exercise not in fitness centers, but on the outdoors. And there are very few women among the fans of extreme tourism. The skin of climbers climbing snow-capped mountains, as well as traveling to the North and South Poles, is exposed to a double danger: extreme climbers can simultaneously get serious sunburn and frostbite. Snow reflects up to 80% of ultraviolet light, so in such conditions, ultraviolet radiation can be especially powerful. In addition, the protective ozone layer of the atmosphere in the area of the Earth’s poles is the thinnest. To protect their eyes from sunlight and reflected light, climbers, skiers and polar explorers must wear sunglasses. It is a vital necessity for them. (By the way, the UV400 marking on the glasses means that the lenses of the glasses do not allow radiation with a wavelength of less than 400 nm to pass through.) And how does wearing glasses affect tanning in normal, non-extreme conditions? Bright sunlight causes the pituitary gland in the human brain to produce melanotropin more actively, a hormone that stimulates the appearance of melanin pigment on the skin in areas exposed to the sun. Therefore, by covering your eyes with sunglasses, you block this tanning mechanism, thereby increasing the risk of sunburn. But dark glasses protect the retina of the eyes, so you shouldn’t throw them away altogether. To avoid skin burns, you just need to take precautions: in southern resorts, you should not sunbathe in the hottest sun — from 11 to 15 o’clock, and you should not stay in the sun for more than 30-40 minutes a day.

However, strange fluctuations associated with age contradictions often occur in fashion. Due to the spread of tanning beds among teenagers aged 13-16 in Western countries, a fashion for extreme tanning has emerged, which has even received the special name “tanorexia” (from the English tan — tan), or tan mania. Young girls in Europe and the USA expose themselves to daily radiation in tanning salons, achieving a chocolate shade. They devote all their time, money, and health to this strange activity. In the UK, which is not spoiled by sunny days, tanorexia is taking on epidemic proportions. The British Medical Association and the Institute of Cancer Research have secured a ban on teenagers under the age of 16 visiting tanning salons. In the United States, legislators from one of the sunniest states, California, are proposing to ban teenagers under the age of 18 from visiting tanning salons. The state Senate even intends to pass a law prohibiting teenagers from sunbathing in tanning salons unless they are prescribed a tan by their doctor. In 27 other states, teenagers must obtain parental consent to visit tanning salons. This problem has become especially urgent due to the wide availability of all kinds of tanning beds – from stationary professional to home ones. Women who do not think about their future are intensively exposed to tanning beds throughout the year, ignoring the recommendations and warnings of doctors. It seems that the chocolate skin tone is becoming another fashionable trend among young people, evidence of adulthood and a way of self—affirmation – like smoking, alcohol or drugs. However, studies show that restrictive measures are not very effective. Teenagers just don’t want to think about the distant future, when the skin will certainly exhaust its regeneration resources, age and become covered with wrinkles.

The skin is wonderfully designed and performs many very complex functions. Many properties of the skin still remain unsolvable mysteries. The skin is closely connected to the brain by a multitude of nerves and nerve endings, and this feature creates some strange and unexplained effects. Why and, most importantly, why do we get goose bumps? Doctors call these pimples on the skin by the term cutis anserina. At the same time, our sparse hairs stand on end, as if trying to protect us from hypothermia, although the attempt is always hopeless. We probably got the “goose bumps” effect from primates, which have much thicker fur. Compared to gorillas, chimpanzees, and orangutans, humans have lost most of their hair. But just like them, we experience a contraction of the smallest muscles of the arrector pili skin, which react to cold and surround the hair sacs. Although people live on the planet in very different climatic conditions, no nation or ethnic group is an exception, although goose bumps do not occur on the heels and palms — there are no hairs and hair sacs. But why are there no pimples on the face and head? Riddle. Eskimos are one of the most hairless people on the planet. If the hair protects the face from the cold, it is strange that the Eskimos have so few of them. This fact has not yet been clearly explained. Or, for example, why do we blush? Why is shame or embarrassment sometimes manifested by an unexpected reddening of the skin of the face? Moreover, such an emotional reaction is caused not by every shame or embarrassment, but only by those that are somehow connected with our social relations in the social hierarchy. Many people have tried to explain the mechanics of redness. Charles Darwin devoted an entire chapter to this in his book “The Expression of Emotions in Humans and Animals.” Sigmund Freud argued that people blush because blushing is related to an internal subconscious struggle between the “Id” and the “Superego.” But until now, this extremely interesting phenomenon remains an unsolved mystery. Another mystery is tickling. A person cannot tickle himself, and someone else must tickle us. And for some, tickling causes a smile or cheerful laughter, especially among children. And for some, tickling can be more unbearable than pain. That is, you can literally tickle yourself half to death.

The desire to avoid excessive UV exposure has led to the creation of self-tanning products that allow you to “get cold” without the sun or a solarium at all. Manufacturers advertise them as a healthy alternative to tanning beds. Bronzers contain special dyes that color the skin. The component dihydroxyacetone contained in the bronzants accelerates the formation of melanin in the skin and colors it in various shades of brown. To apply such a self-tan, you need to have the skills, otherwise the “coloring” may turn out to be spotty. The main difference between bronzers and real tanning is not only in speed (some allow you to color your skin in a few minutes), but also in the fact that the dyes can dissolve under the influence of sweat or water, washing off prematurely and leaving stains on clothes. For those who still prefer the natural way, special “tanning pills” have been created that accelerate skin pigmentation several times during tanning. They contain the substance contactxanthin, which is deposited not only in the skin, but also in other organs, such as the retina of the eye. However, many doctors do not recommend using these drugs because of the many side effects (they are not allowed in many Western European countries and in the USA). Another novelty is accelerators, or tanning enhancers. The main mechanism of their action is to accelerate the synthesis of melanin, which turns the skin dark. The active ingredient in accelerators is the amino acid tyrosine. Although tyrosine is non-toxic, too little data has been collected on the effects of its prolonged use, which is why tyrosine-based tanning accelerators are banned in the United States and Western Europe. Source: Popular Mechanics Photo: vtemu.by