Sunscreen, is the three volts day out of the necessary courses. Wash on the sunscreen, wear a sun hat, open the sun umbrella ...... everyone has their own sunscreen secret, but recently saw such a hot search # girls excessive sunscreen osteoporosis!

Recently, a 95-year-old girl in Fujian went to the hospital for long-term chest, waist and back pain and discomfort. The results of the examination showed that the girl because of the lack of exposure to sunlight, resulting in bone loss, suffering from osteoporosis. Doctors learned after questioning, the girl has long been working in a building, even if you go out is also the whole body package sunscreen, exclude related diseases that its condition is related to excessive sunscreen. What are the dangers of excessive sun protection? What is the effect of the sun on the skin? How to sunbathe scientifically?

1. What are the dangers of excessive sun protection?
In recent years, a number of studies have shown that excessive sun protection may lead to a deficiency of vitamin D. Vitamin D is a fat-soluble vitamin that regulates calcium and phosphorus metabolism in the human body, and plays a role in maintaining healthy bones. Adults lack of vitamin D will cause increased bone loss, osteoporosis, fracture risk increases, the body will appear back pain, mobility, cramps and numbness, muscle weakness, bone pain, excessive sweating, hair loss and other symptoms, the human body immune system will also be reduced. Children with chronic vitamin D deficiency can easily lead to rickets.

Generally speaking, blood serum 25-hydroxyvitamin D is less than 30mg/ml is vitamin D insufficiency, less than 20mg/ml is vitamin D deficiency, less than 12mg/ml is vitamin D severe deficiency.A survey in 2017 showed that 86% of the people in the country are vitamin D deficient or insufficient, and the prevalence of vitamin D deficiency among urban residents is significantly higher than that of rural residents.

And there are two main sources of vitamin D in the human body: one is under sunlight or ultraviolet irradiation, synthesized by chemicals in the skin, and about 80% of the vitamin D in the human body is obtained through this channel; the second is obtained through dietary sources, such as fatty fish and fish eggs, animal liver, egg yolks, cheese, and part of the fungus and mushrooms, etc., but the proportion of intake from food sources alone is relatively low, and it can't satisfy the daily requirements. Sun exposure is the best way to take vitamin D supplements.

Excessive sun exposure can also lead to sleep or mood problems. 2022 study published in the journal Advances in Psychological Science describes that intrinsic light-sensitive ganglion cells in the retina project light signals to brain regions involved in mood regulation, which directly affects mood.

Prolonged absence of sunlight can lead to reduced melatonin secretion in the body, affecting sleep quality. Sunlight helps to regulate the body's biological clock and circadian rhythms, and there is a wealth of research showing that exposure to sunlight promotes the synthesis and release of neurotransmitters such as serotonin and dopamine, which are essential for maintaining mood stability and feelings of pleasure. Lack of sunlight may lead to decreased levels of these neurotransmitters, increasing the risk of depression.

A large study of British adults totaling more than half a million people showed that the more time spent outdoors in the light during the day each day, the fewer depressive symptoms and the lower the odds of using antidepressant medication. In addition, many studies have shown that insufficient light is a major contributor to seasonal depression, and light therapy has been utilized as a first-line treatment for seasonal depression in treatment guidelines to reduce depressive symptoms.

Additionally, overprotecting yourself from the sun in order to look beautiful may be counterproductive. Sunscreen clothing, even if made thin and comfortable, worn in hot weather of more than 30 degrees Celsius will cause the skin to swelter, sweat does not evaporate in time, which in turn causes allergies, prickly heat or acne. Physical sunscreen products such as masks, if not cleaned every day, stained with cosmetics, dust and sweat, more likely to breed bacteria, resulting in acne, inflammation and other problems.

2. How does the sun affect the skin?
Skin is the largest organ of the human body, healthy skin can not only resist the external adverse environment or harmful substances of the intrusion, but also is the foundation of the beauty of people beautiful and confident. According to the survey, Chinese people see healthy and beautiful skin should be fair, moist and elastic, no wrinkles, uniform color, and these appearances will be affected by the aging of the skin.

In addition to the natural aging of human skin, it is also susceptible to the effects of ultraviolet rays in the sun, resulting in “photoaging”. The sunlight we come into contact with every day is actually a band of light, composed of electromagnetic waves of different wavelengths. Sunlight reaches the Earth's surface mainly in ultraviolet, visible light and infrared light, our eyes can only recognize visible light, ultraviolet, infrared light we can not see. Visible light accounts for about 50% of the sun's radiant energy, infrared light accounts for about 43%, and ultraviolet light accounts for the least percentage, only about 7%.

Because UV light has high photon energy, although it accounts for the smallest percentage, it causes the most damage to the skin. Ultraviolet light can be subdivided into long-wavelength UVA, medium-wavelength UVB and short-wavelength UVC.

Short-wavelength UVC is generally blocked by the ozone layer from reaching the earth's surface. Medium-wave ultraviolet UVB can promote mineral metabolism and vitamin D formation in the body, but long-term or excessive exposure will cause skin redness, swelling, heat, pain, and in severe cases, blisters or peeling, we usually say that sunburn is caused by UVB.

Long-wave ultraviolet UVA is the most penetrating type of ultraviolet, can penetrate glass, can also reach the dermis layer of human skin, destroy collagen and elastic fibers, thus causing skin relaxation and aging, accelerating the formation of wrinkles, and can promote the formation of skin melanin, resulting in skin darkening, inducing or aggravating freckles, chloasma and other pigmentation, and the most damaging to the skin.

3. How to scientifically “embrace the sun”?
The pursuit of beauty is very important, but the health of human body and mentality are also more important. Contrary to the trend of “heavily armed” sunscreen, some young people are now “embracing the sun”. Three days, young people set off a “sun back” trend, some netizens said that after the sun back, “they seem to become more energetic”, “not easy to cold hands and feet”.

Peking Union Medical College Hospital dermatologist Sun Qiuning said, whether it is adults or the elderly children, in the case of avoiding heat stroke should ensure that every day there is a certain length of time in the sun, the benefits of bone health. In addition, it is not recommended that children apply sunscreen, bone growth and development stage of the child needs sun absorption of calcium, premature, excessive sunscreen instead of the body is not beneficial.

Want to sunbathe, but do not want to be tanned and sunburned, how to scientifically “embrace the sun”? Sunbathing, first of all, is to choose the right time and place, “embrace the sun” should try to choose the outdoors, to avoid the sun “hot” time. Studies have shown that, through the window glass, the transmission rate of the required band of ultraviolet radiation is less than 50%, if 4 meters from the window, only 2% of the outdoor. Therefore, if you have to sunbathe indoors, you should open the window and let your skin come into direct contact with the sun.

In addition to pay attention to the local weather forecast, look at the length of the shadow to determine the timing of the sun is a good way that when the length of the shadow is shorter than the height, should not come out of the sun; when the shadow is 2 times the height or even more, the UV index is the most secure, you can do not need to protect the sun, a good sunbathing; when the shadow in the 1 to 2 times the length of the body height, sunbathing length of time to control the most secure in 20 minutes; when the shadow shorter than the height of the body, the UV may be in 30 minutes, the sun is the most secure. When the shadow is shorter than your height, UV rays may cause damage to your skin within 30 minutes.

As for the length of time, adults should sunbathe for 30 minutes to 1 hour per day, while infants and children with delicate skin are prone to sunburn, so it is recommended to sunbathe for 15 to 30 minutes per day.

It should be noted that cataract patients need to wear protective glasses to prevent UV rays directly into the eyes. After eating cilantro, parsley, mango and other “photosensitive food” should pay attention to sunscreen, some of the ingredients are more likely to cause sunburn.

Moderate sunscreen, not only can prevent sunburn, photoaging and skin cancer and other problems, but also make life easier, the World Health Organization advocates sunscreen “ABC” principle.

A is Avoid, that is, to avoid being sunburned, 10:00 am to 4:00 pm UV intensity of the highest time try to avoid outdoor activities, stay indoor activities are appropriate. However, the time varies according to the local latitude and the intensity of local sunshine. Before going out, you should pay attention to the local UV index of the day.

B is Block, that is, physical blocking, the use of umbrellas, hats, etc. to reduce the direct exposure of ultraviolet radiation on the skin, it is recommended to buy UPF greater than 40, UVA value through rate of less than 5% of the sunscreen products.

C is Cream, that is, apply sunscreen, weekday travel, you can use SPF value between 15 to 50, PA + to + + + sunscreen or isolation cream. SPF is the Sun Protection Factor Sun Protection Factor of the acronym, on behalf of the ability to resist UVB, the greater the value of the SPF, the greater the effect of preventing sunburn erythema, sunburn, but also impede the synthesis of vitamin D. PA is the Protection Grade of UVA, on behalf of the ability to prevent UVA, the higher the PA grade, the better to prevent skin tanning, sun aging effect. PA is the abbreviation of Protection Grade of UVA, representing the ability to resist UVA, the higher the PA grade, the better the effect of preventing skin tanning and sun aging.

The World Health Organization recommends applying sunscreen products 15 minutes before going out. Regular products need to be reapplied every 2 to 3 hours. The amount of application to the size of a penny product applied to the full range of the Department of the appropriate, already exists in the vitamin D deficiency of the population, can be appropriate to reduce the use of sunscreen parts and chances.