Shulou(Shulou.com)11/24 Report--

This article comes from the official account of Wechat: back to Park (ID:fanpu2019), author: Wang Chenguang

The title of the original text: "the middle-aged man dies of melanoma, and the efficacy of ultraviolet rays is beyond your imagination."

The benefits of ultraviolet rays go far beyond the synthesis of vitamin D, and the harm goes far beyond causing skin cancer. Balancing the positive and negative effects of ultraviolet rays in sunlight may be more important than you think.

Written by Wang Chenguang (Doctor of Biology and former Professor of Union Medical College)

The news that 37-year-old singer Zhang Hengyuan died of melanoma has made skin cancer hot again, and ordinary people who talk about cancer color change once again struggle with whether to go outdoors to bask in the sun: less sun worried about insufficient synthesis of vitamin D. too much sun worried about skin cancer.

Either way, their concerns are incomplete: the benefits of ultraviolet rays go far beyond the synthesis of vitamin D, and the harm extends far beyond the cause of skin cancer. It is necessary for us to have a more comprehensive understanding of ultraviolet rays and the relationship between skin cancer and sun exposure.

Four types of skin cancer and three types of ultraviolet rays on June 18, Father's Day, the author took part in a mountain cross-country race in Jizhou, Tianjin. The race began at 7 a.m., when the temperature was 24 degrees and there was a breeze in the shade. It was comfortable, but after 10:00 the temperature rose sharply and soon reached 34 degrees. As the shadow cast on the ground became shorter and shorter and the sweat became more and more, the burning sensation of the sun shining on the exposed skin gradually increased. At this time, my fellow runner said, my face is red in the sun.

What are the factors that cause these changes in our feelings and bodies?

First of all, the infrared light in the sun is absorbed by the skin, so we feel hot. This is the same as feeling warm by the fire in winter.

Then the skin turns red, which is because the ultraviolet (UV) in the sun irradiates on the skin, causing the blood vessels under the epidermis to dilate, causing the skin to turn red. This is also a warning, after this situation, if you avoid the sun in time, usually the red skin can return to normal the next day. If you continue to be overexposed to ultraviolet light, it can cause skin damage, sunburn or sunburn.

The skin darkens easily in summer because ultraviolet rays stimulate the melanocytes in the skin to produce more melanin. This is a protective mechanism formed when the skin is exposed to ultraviolet rays. Once something goes wrong with this protective mechanism, the consequences can be very serious. Melanoma, the most malignant skin cancer, is the result of canceration caused by melanin-producing cells that are often exposed to ultraviolet rays.

There are four main types of skin cancer (three outdated ones). The most common occurrence is basal cell carcinoma, which accounts for about 80% of skin cancers. Basal cell carcinoma occurs most often in the head and neck and is mainly caused by sunlight; a small amount is due to radiation therapy in childhood. This type of skin cancer usually grows slowly and rarely spreads to other parts of the body and causes death.

The second highest incidence is squamous cell carcinoma, a tumor that occurs on the surface of the skin, accounting for about 20% of all skin cancers. Squamous cell carcinoma is also mainly caused by sunlight. The above two types of skin cancer are sometimes grouped into one category, that is, skin keratinocytic carcinoma.

Melanoma is also a type of skin cancer, named after the melanocytes that occur in the skin. Although melanoma accounts for less than 1% of all skin cancers, melanoma is the most malignant type of skin cancer and the most prone to metastasis. 2/3 of skin cancer deaths come from this type.

There is also a skin cancer that is not often mentioned-Merkel cell cancer. This is an extremely rare, highly invasive or fast-growing malignant tumor. The occurrence of this kind of tumor is related to a hormone-secreting cell in the skin, so it is also known as cutaneous neuroendocrine carcinoma. Recent studies have found that this kind of tumor is closely related to a viral infection and is the least closely related to the sun in skin cancer.

Melanoma is most closely related to ultraviolet radiation. Sunlight is the most common source of ultraviolet radiation, so sun exposure is the main risk factor for melanoma.

Before we can learn more about how to protect against sun-induced skin cancer, we need to understand ultraviolet rays and how ultraviolet rays cause harm to the skin.

Ultraviolet is a part of the electromagnetic radiation from the sun to the earth, which can be divided into UVA, UVB and UVC according to the wavelength from long to short. UVA is the longest of the three kinds of ultraviolet rays, with a range of 320nm and 400nm, and the wavelength range of UVB is 290nm and 320nm. The shorter the wavelength, the higher the energy. As for UVC rays with shorter wavelengths, humans living at low altitudes need not worry. Most of them will be absorbed by the ozone layer, making it difficult to reach near the ground.

Both UVA and UVB can penetrate the atmosphere and are responsible for premature skin aging, eye damage (including cataracts) and skin cancer. The International Agency for Research on Cancer (IARC) classifies UVB and UVA as Class I (sufficient evidence) and Class II (sufficient evidence) carcinogens respectively.

We spend much of our lives exposed to UVA light, and UVA can penetrate the skin through clouds and window glass. Ninety-five percent of the UV light that reaches Earth is of this type. Although it doesn't carry as much energy as UVB, it is dozens of times more energetic than UVB. As long as the sun comes out, there is UVA, and the intensity is relatively balanced, so we should pay attention to protecting UVA all the year round.

UVA can penetrate deeper skin and is responsible for blackening, aging and wrinkling. The role of UVA in the development of skin cancer is still controversial. The current consensus is that UVA increases the risk of skin cancer, but it is not as serious as UVB. Sunbathing uses artificial light, and the light component is mainly UVA, which is more than 10 times higher than that in the sun. People who regularly sunbathe are 2.5 times more likely to develop squamous cell cancer and 1.5 times more likely to develop basal cell cancer, while regular sunbathing increases the incidence of melanoma by 75%.

UVB is also known as outdoor ultraviolet light, because it cannot penetrate glass to get indoors, and it is difficult to penetrate the surface layer of the skin to reach the deep layer. It mainly damages the more superficial part of the skin, but it is the main cause of skin dark spots and skin cancer. At the same time, it can also make the skin turn red and tanned. The intensity of UVB varies with time, place and season of the day. There is a strong UVB in most parts of China from April to October and from 10:00 to 4 pm every day. Ultraviolet rays are stronger at high altitudes, so they are more likely to be exposed to higher doses of UVB radiation when cross-country or hiking in the mountains.

Another serious harm of ultraviolet rays: damage to immune function, since then, we have recognized the negative effects of ultraviolet rays on health, especially in the pathogenesis of skin cancer. More than one million people worldwide suffer from skin cancer every year, and fair-skinned people are more likely to develop melanoma after exposure to ultraviolet radiation. So, how does ultraviolet radiation cause skin cancer?

Almost all cancers are the result of genetic mutations, and skin cancer is no exception. The energy of ultraviolet rays is enough to destroy the genetic material (DNA) of human epidermal cells, causing DNA to break. It is estimated that hundreds of thousands of human epidermal cells are damaged by ultraviolet rays every day.

Human cells have a powerful repair function, some of the damaged DNA are repaired, and those that cannot be repaired can hardly survive. The chance of getting cancer occurs in the process of damage and repair, which leads to changes in gene sequence (mutations), some of which lead to changes in cell proliferation behavior. These changes accumulated for a long time, and finally induced normal cells to complete the transformation to tumor cells at a certain point in time.

The above are the "internal causes" of normal cell carcinogenesis. But not all altered cells develop into tumors, because the body's immune system monitors these changes and destroys them in time. In other words, the eventual occurrence of tumors often requires the cooperation of another force, mainly immune deficiency. The reason for the higher incidence of tumors in the elderly is that, on the one hand, the accumulation of gene mutations in the above-mentioned cells, and another important factor is the gradual decline of immune function with aging.

Does this have anything to do with skin cancer induced by ultraviolet rays? Yes, and it matters a lot, because ultraviolet rays can inhibit immune function.

The skin is the largest immune organ of the human body, which not only provides a physical barrier between the body and the outside world to prevent microbial invasion and water loss, but also distributes a large number of immune cells in the skin to perceive and resist the invasion of pathogens. The inhibition of UV on immune function is reflected in many aspects: for example, UV can directly inhibit the function of many kinds of immune cells (such as T cells, B cells, natural killer cells and macrophages); long-term UV exposure may lead to the death of immune cells, thus reducing the number of immune cells. Ultraviolet radiation can also interfere with the regulatory mechanism of the immune system, inhibit the production of anti-inflammatory cytokines, increase the release of inflammatory cytokines, and lead to immune response imbalance, thus weakening the monitoring and clearance of skin immune function to tumor cells.

The inhibition of skin immune function by high-intensity UV exposure is the result of long-term evolution of human and nature, and is the protective mechanism of the body against high-intensity UV. Doesn't that sound a little paradoxical? It's not contradictory. Ultraviolet rays kill skin cells and cause the body's excessive immune response (which is why some people are allergic to ultraviolet rays). This immune response is even more harmful to the body than ultraviolet rays itself. the result of evolution is that the body has a mechanism against this damage, that is, the immune response is suppressed while exposed to ultraviolet radiation.

UV suppression of immunity may increase the risk of infection, reduce the surveillance of tumor cells, and aggravate the development of autoimmune diseases; however, moderate UV exposure is also necessary to maintain normal immune function. such as improving the symptoms of some skin diseases and autoimmune diseases. Ultraviolet rays have other positive effects, such as synthesizing vitamin D, regulating hormone production and secretion, improving mood and so on. Although UVA can not promote the synthesis of vitamin D, it can promote the synthesis of nitric oxide. Nitric oxide can help lower blood pressure and relieve depression. It has many benefits to the body.

Therefore, balancing the beneficial and adverse effects of ultraviolet rays in sunlight is the key to ensuring health.

When should I avoid being in the sun? Here to teach you a simple method, also known as the "shadow rule" (applicable to low altitude areas): if you stand in the sun, the shadow is shorter than the height, then the sun ultraviolet rays in the most harmful to the skin UVB is very strong, this period of time is not suitable for long time in the sun to do unprotected activities If the shadow is longer than the height, the UVB in the light decreases, which is suitable for outdoor activities, which can synthesize vitamin D without getting sunburned quickly.

For outdoor enthusiasts, the following general methods should be used as guidelines: try to avoid outdoor activities during periods when the sun is strongest (usually from 10:00 to 4 p.m.); spray sunscreen, choose sunscreen with an SPF index of more than 30, and pay attention to reading instructions to ensure that you can resist UVB; wearing a long-sleeved shirt, trousers and wide-brimmed hat to minimize direct skin exposure to the sun. Sunglasses can block almost all ultraviolet rays; try to stay under shade or umbrellas to reduce sun exposure.

Judge melanoma, far away from misunderstanding, so how to judge whether the nevus on the skin is melanoma? Many popular science articles in China have introduced a method of self-judgment, that is, ABCDE method.

From the morphological point of view, A (Asymmetry) refers to whether the nevus is symmetrical, the more irregular and asymmetric the edge is, the higher the risk of melanoma; B (Border) refers to the boundary, the boundary is unclear and toothed, the risk is high; C (Color) refers to the color, the risk of single and uniform color is lower; D (Diameter) is the diameter, for the irregular edge of the nevus, the risk of the long diameter is greater than half a centimeter. Finally, E (Evolution) refers to the dynamic process, that is, whether the mole or spot has changed in the past few weeks or months.

It is necessary to highlight the last point here. E is the abbreviation of evolution or evloving in English here, but it has been changed to elevation incorrectly in the simplified world. The difference between a word is a thousand miles away. The former means "progress", which is the most important indicator of whether moles on the skin become cancerous or not. While the latter refers to "uplift", some of the so-called popular science celebrities in China have made a big mistake here, thinking that the suspicious mole-like tissue on the skin will be higher than the skin. On the contrary, the most malignant melanoma in skin cancer usually appears as a flat shape rather than protruding from the surface of the skin.

Genetic factors play an important role in tumorigenesis, exceeding the environmental impact, but today's science can hardly prevent or treat cancer from the perspective of genetic change. what we can do is to minimize the risk of environmental carcinogenesis.

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