Sunscreens and skin cancer: details

Are you from burns or from cancer?

Nadezhda Markina, "Newspaper.Ru»

At the height of summer "Newspaper.Ru" figured out how and what sunscreen cosmetics protect us from, as well as why we use sunscreen products more, and the incidence of melanoma is growing.

How does the protection factor protectWhen choosing sunscreens, most people rightly focus on the SPF protection factor.

This abbreviation comes from the English Sun Protective Factor and denotes the sun protection factor, which characterizes the degree of protection provided by this cream. SPF is indicated in large numbers on each bottle. The higher the number, the greater the protection.

Before using sunscreens, you need to realize what type of skin nature has given you. It depends on the production of melanin, a dark pigment that is contained in the cells of the epidermis and absorbs light. If there is a lot of melanin, a person has naturally dark skin, at the same time he tans well and does not burn in the sun. If there is not enough of it, a person has very light skin, which turns red and burns even with a short stay in the sun. Often the owners of such skin have red hair. Most often, the skin belongs to an intermediate type, and there are six phototypes in total.

For the first and second phototypes (light-skinned), a high protection factor is needed (SPF > 20), for the fourth and sixth, a fairly low one (SPF < 10).

It is believed that the number of the protection factor indicates how many times longer you can stay in the sun, smeared with cream, than without it. For example, if without cream your skin turns red in the sun for half an hour, then with SPF4 cream this time increases to two hours.

Redness of the skin (erythema) is the first stage of sunburn, and then, as you know, the skin peels off, the upper layer of the epidermis comes off. No one wants to get burned in the sun, and that's why we use protective equipment. They protect the skin from burns.

From burn to cancerBut red and peeling skin is not all the troubles we get from the sun.

Radiation in the ultraviolet (UV) range damages skin cells, which leads to their increased aging (photoaging) and increases the likelihood of skin cancer, primarily its most dangerous type – melanoma. This is because UV radiation damages biological molecules. Under its influence, photochemical reactions occur, leading to the appearance of free radicals – molecules with an unpaired electron that spoil proteins and DNA. If the skin protein collagen is damaged in this way, the skin ages intensively. If the changes affect the DNA, the cell can become cancerous.

In the solar spectrum, UV radiation is divided into three ranges depending on the wavelength. The shortest rays of UV-C (200-290 nm) practically do not reach the Earth's surface due to the atmosphere and its ozone layer; UV-B (290-320 nm) and UV-A (320-400 nm) are what our skin gets. But they act differently.

UV-B, as a shorter-wave radiation, has more energy and burns the skin more, which is what we are most afraid of. UV-A at first glance more harmless radiation, it does not burn so much, but penetrates deeper into the cellular layers of the skin, into the dermis. This means that it is this range of ultraviolet light that brings with it dangerous consequences – photoaging and cancer.

Accordingly, the letters UVB or UVA are indicated on the bottle with sunscreen. For example, UVB means that the product protects you only from UV-B rays, that is, only from sunburn. But on modern means of good brands, as a rule, the letters UVA, circled in a circle, are also indicated. This means that the product protects not only from UV-B, but also from UV-A rays.

For those who want to tan, it would be interesting to know: will some amount of ultraviolet light break through the double protection to get a beautiful skin tone? In addition, ultraviolet light is "not only harmful, but also useful": under its influence, vitamin D, which is extremely important for the body, is synthesized in the skin and various other beneficial processes occur. For example, blood pressure decreases, and with it the risk of heart attacks and strokes.

Lovers of a tanned body do not have to worry: completely without ultraviolet radiation, the body will not remain even with protective means. Firstly, they are usually not smeared on the skin with a thick enough layer (the norm is 2 mg of cream per 1 cm ²), so they still do not work in full force. Secondly, any protection does not eliminate ultraviolet, but only weakens its effect.

Another important factor to consider is that the spectrum of solar radiation varies at different times and at different latitudes. At noon (astronomical time), the intensity of radiation at a wavelength of 290-320 nm (B-band) is ten times higher than at 9.00 or 15.00.

The reason is that the sun is higher above the horizon at this time, and in the morning and evening hours it falls to the earth with oblique rays that travel a greater distance in the atmosphere and dissipate more strongly. For the same reason, the intensity of short-wave radiation is greater the closer it is to the equator. In other words, going on a trip to the tropics, you need to keep in mind that the sun will burn harder not only with heat, but also with ultraviolet. And, accordingly, to increase the level of protection. More intense ultraviolet light is also in the mountains, increasing by about 6% with each kilometer of altitude.

Do cancer creams helpDo sunscreens protect against cancer?

Science and medicine do not yet have an unambiguous answer to this question.

Optimism is hampered by the fact that the incidence of skin cancer, including melanoma, is growing in the world. Although, it would seem, it should decrease, because people are now using sunscreens much more.

According to the World Health Organization (WHO), more than 130 thousand cases of melanoma and 66 thousand deaths from melanoma and other forms of skin cancer are registered annually in the world. Compared with the middle of the last century, by the beginning of the XXI century, the incidence of melanoma increased sixfold. The highest level is observed in those countries whose population has fair skin and where it is customary to sunbathe in the sun: in Australia, New Zealand, North America and Northern Europe. In Norway and Sweden, the annual incidence of melanoma has more than tripled over the past 45 years, in the United States it has doubled over the past 30 years. The highest rates of melanoma were recorded in Australia, where many residents are from Northern Europe and live in a climate with significantly more solar radiation.

Experts have three hypotheses explaining why people use sunscreens more often, and melanoma is growing.

Firstly, this type of skin cancer develops slowly, its latent period is 20-40 years. So, perhaps, the current victims of melanoma received a dangerous dose of radiation in their early youth, when sunscreens were not yet so popular. And the fashion for tanning began in the 1950s, when tanned skin became a sign of well-being and prosperity.

Secondly, the ozone layer of the earth's atmosphere becomes thinner, which reduces the effectiveness of its protection from ultraviolet radiation. Perhaps this is the answer to the question, but how did we all live before, going out in the sun without any creams? The sun was less aggressive.

The third hypothesis is the most unpleasant: perhaps sunscreens not only protect against cancer, but also provoke it themselves. Feeling safe, people, smeared with cream, spend much more time in the sun, while they may not apply the cream on the whole body or less than necessary, or wash it off with water (experts say that waterproof products are a myth). Thus, they receive a large exposure to UV-A radiation along with the risk of getting cancer.

Finally, those substances that work in sunscreens and sprays may themselves be unsafe. They include physical UV absorbents that reflect and scatter the sun's rays, such as zinc oxide and titanium dioxide. Another group of protective substances are chemical UV filters that reduce the effect of radiation on cells. If you read their list on the package, few people will like the names: paraaminobenzoic acid (PABA), although many manufacturers have already abandoned it, since it can cause allergies; octyl methoxycinnamate, benzophenone-3, 4-isopropyldibenzoylmethane, etc. They penetrate the skin, and how they act with prolonged use, has not really been studied yet. For example, a 2001 report issued by the Environmental Working Group (EWG) states that many popular sunscreens contain ingredients that may be carcinogens.

Studies that have tried to objectively prove whether sunscreens protect against cancer give contradictory results.

Here is what is said in the European recommendations for the fight against malignant tumors, which are given on the website of the Cancer Society of Russia: "These drugs can serve as protection against squamous cell carcinoma, but currently there is not enough convincing evidence that they have a protective effect in the case of basal cell carcinoma and melanoma. When using them, it is very important to avoid increasing the duration of exposure to the sun, which can lead to an increased risk of developing melanoma."

American scientists from Memorial Sloan-Kettering Cancer Center, having analyzed the relationship between the use of sunscreens with squamous cell carcinoma, basal cell carcinoma and melanoma, say: the products protect against these types of cancer and do not lead to vitamin D deficiency, but only when applied correctly to the skin.

According to the data provided by an oncodermatologist, experts representing the International Agency for Research on Cancer studied the preventive effect of using sunscreen on the development of skin cancer. They found that the use of a protective cream can prevent erythema and squamous cell carcinoma. For basal cell carcinoma and melanoma, this effect has not yet been determined due to the difficulty of studying a long latency period. Paradoxically, there is conflicting evidence that the use of sunscreens can increase the risk of developing melanoma with increasing time in the sun.

Of the 15 studies, only 3 showed a significant reduction in the risk of melanoma, 4 showed no significant effect, and 8 showed an increase in risk.

Solar circle – the sky aroundHow to protect children from the sun is a separate issue.

Dermatologists emphasize that excess ultraviolet radiation in childhood is most dangerous for the risk of developing melanoma during life. The child has a very thin epidermis, and melanocyte cells that produce melanin begin to work only by the end of the second or third year of life.

Is it worth smearing children with sunscreen cosmetics? Spanish scientists who have studied this issue claim that an oil-based emulsion containing physical filters is best suited for children. Although it is also impossible to do without chemical filters in order to achieve the SPF-50 protection factor, which is recommended for children. But at the same time, oxybenzone and octocrylene should be avoided in the composition.

And it is best to keep smaller children in the sun at noon and put on light cotton clothes and a panama hat on their heads. Russian pediatricians believe that a child should not be under the scorching rays of the sun at all until the age of three, and from the age of three – no more than 15 minutes.

And adults should remember that no protective cosmetics will replace the head on their shoulders. The sun in large quantities, like alcohol, is dangerous for your health.

Portal "Eternal youth" http://vechnayamolodost.ru01.07.2014