Sunscreens. Part 3


Sun protection is only possible in a few basic ways. We invite you to get to know each of them in more detail.

How to protect your skin from the sun?

There are three ways we can protect our skin from UV rays: make them reflect, deactivate them, and finally repair or repair the damage they cause. Chemistry allows you to go any of three ways. In the United States and Europe, people spend about $200 million annually on creams with physical and chemical filters. However, most consumers are unaware that applying a sunscreen oil or cream in the morning may not be enough to provide long-term UV protection, as it is likely that the product will be washed off during the day, either through sweat during intense exercise or water during bathing. When, being in a cool pond, we feel invigorating freshness, this does not mean that ultraviolet rays do not affect us, this type of electromagnetic radiation easily passes through the water. Silicone oils, which are inherently water-repellent, are added to some creams to provide long-lasting protection for those who exercise in the sun or swim in open water on sunny days.

A good sunscreen should contain titanium dioxide or zinc oxide to protect the skin from UV-A rays and organic ingredients to protect against UV-B; it should be easy to apply to the skin, create long-lasting protection and be invisible. Sunscreen should not be sticky and should not be washed off while swimming, but it should be easy to wash off in the shower with soap or gel. Bacteria should not grow in the cream, and it should smell good. And, of course, the product must provide reliable and long-term sun protection with a coefficient (SPF — sun-protection factor) of at least 15.

SPF protection factor

The protection factor is the degree to which a sunscreen protects the skin from UV rays, and ranges from 2 to 30 or more. The coefficient is calculated from the ratio of the time required for the occurrence of a burn on the skin protected by the agent, and the time for which the burn is formed on the unprotected skin. For example, if a burn occurs on unprotected skin after two hours, and on protected skin after twelve hours, then the protection factor of the cream can be calculated by dividing 12 by 2, and it will be equal to 6. Thus, the protection factor allows you to evaluate the degree to which sunscreen limits UV exposure to the skin. At a factor of 2, ultraviolet radiation is reduced by 50%, and at a factor of 4, only 25% of the UV rays reach the skin, while 75% of the radiation is absorbed, at a factor of 10, ultraviolet rays are absorbed by 90%, and at a factor of 25, by 96% and penetrates into the skin only 4% UV. Theoretically, it is possible to achieve a protection factor of 50, a product with this coefficient will block 98% of UV rays, but for now, manufacturers can offer us creams with a maximum protection factor of just over 30.

Initially, sunscreens with a factor of 10 were considered reliable protection from the sun, but today some restless consumers use products with a factor of 30, as a result, during a two-week vacation, subject to regular use of a sunscreen, such people receive a lower dose of ultraviolet radiation than during a one-day exposure to the sun with unprotected skin. Protection factor values ​​can be misleading, some people might think that a cream with a factor of 30 protects the skin twice as effectively as a cream with a factor of 15. This is not true, in this example, a stronger agent is only 4% more effective in protecting the skin compared to a more weak. A cream with an SPF of 30 will absorb 97% of UV rays, while a cream with a SPF of 15 will absorb 93% of UV rays.

A standard sunscreen lotion contains 5% titanium dioxide, 5% some kind of chemical filter, 10% various oils, 5% emulsifier, and the remainder is distilled water. The role of the emulsifier in this mixture is to prevent the water and oil from separating into two layers. The lotion also requires the presence of a preservative to protect it from microorganisms.

Reflection of the sun’s rays

The best way to achieve reflection of UV rays from the skin is to apply a layer of zinc oxide (ZnO) or titanium dioxide (TiO2) on it, both of these white substances are part of the “zincy” ointment, which serves to protect the most vulnerable skin areas from the sun, such as the nose, cheekbones and lips.

Those who need to spend a lot of time in the sun, such as farmers, builders, athletes, use similar ointments. Thanks to the efforts of pharmacists, less noticeable forms of these drugs have been created, and zinc oxide and titanium dioxide are added to sunscreens, but in such proportions that they remain invisible.

The trick with titanium dioxide is to use micrometer or nanometer particles of this substance, which are invisible to the naked eye, the optimal size for them is considered to be 50 nm. When chemical and physical filters are used together, these substances enhance the effect of each other, so it turns out that a smaller amount of each of them is required. However, some sunscreens can interfere with each other, for example, a number of organic sunscreens cause microparticles to stick together, thereby weakening their protective potential, and at the same time make the sunscreen visible on the skin due to the formation of large white metal oxide clusters. The addition of silicone oil to sunscreen prevents caking by holding titanium and zinc oxides in microparticulate form. Another way to counteract the whitening effect of titanium dioxide is to bind it to the mica particles, which will keep your skin’s natural color when sunscreen is applied.

Sunlight absorption

The second way to protect the skin is to create a transparent protective film on its surface that would absorb and neutralize dangerous UV rays. There are many different UV absorbers, all of which neutralize sunlight in different ways. For example, ortho-hydroxybenzophenone absorbs the energy of electromagnetic radiation with a wavelength of about 330 nanometers, due to this energy one of the hydrogen atoms of the absorber molecule passes from its oxygen atom to the neighboring oxygen atom of the same molecule. As a result, the molecule is in an unstable high-energy state, then the reverse transition occurs with the release of energy in the form of heat, which does not harm the skin.

Other substances act according to a similar mechanism, in which an electron excited by ultraviolet passes to the outer orbital of the atom, from which it soon returns to its original position, transferring the absorbed energy into the energy of a mechanical vibration. In order for the described transformations to take place, the absorber molecule must contain a special chemical structure called a chromophore.

More than 6000 tons of sunscreens are produced annually, these include derivatives of aminobenzoic acid, camphor, cinnamic acid, they are mainly effective against UV-B, while benzophenone and dibenzoylmethane derivatives block UV-A rays.

The listed substances belong to chemical filters of an organic nature, since the structure of their molecules is based on a carbon skeleton. All of them are highly soluble in oil, although sometimes the solubility is insufficient for their use in cosmetics, in such cases it is increased by adding simple sugars to the molecules. But even in this case, some of the chemical solar filters cannot be used, as they lose their properties when exposed to the sun or diffuse into the wall of the plastic container.

Skin restoration

The third way to protect is to repair the damage caused by UV rays, for this, so-called free radical scavengers are used. The fact is that UV rays have sufficient energy to break chemical bonds, as a result of such a break chemically highly active fragments of molecules are formed — free radicals. Free radicals can interact with almost any chemical structure they encounter along the way, including DNA. The most active radicals are formed from oxygen. When ultraviolet rays hit the molecule of this substance, the so-called singlet oxygen is formed, which is extremely harmful to any biological structures.

sun protection

Our bodies can easily deal with free radical damage to DNA, but UV also damages the immune system, whose function is to detect molecular damage and trigger repair mechanisms. As a result, the likelihood that a DNA mutation will remain undetected is greatly increased. Our body produces special “cleaners” that are able to provide adequate protection against free radicals. Molecules that protect us from free radicals also include vitamins C and E: Not surprisingly, they are added to sunscreen lotions along with other antioxidants, such as polyphenols obtained from grape seeds.

So what do we need to do to protect our skin from the harmful effects of ultraviolet radiation? The best advice is to avoid sun exposure between eleven and fifteen o’clock. For the rest of the day, if you plan to be at the beach or swim in open water, use sunscreen with a factor of 15. If you want to walk, play sports, work in the garden in sunny weather, wear closed clothing and a hat. Clothing is the best protection from the sun. The German chemical company BASF has even released a nylon fabric in which particles of titanium dioxide are embedded. Closed clothing made of such material can be an effective means of protection from the sun.

Sunscreens. Part 1

Sunscreens. Part 2

Source: based on materials from John Emsley’s book «On the benefits and harms of the products we love to buy»

Article protected by copyright and related rights. When using and reprinting the material, an active link to the healthy lifestyle portal is required!


Добавить комментарий

Ваш адрес email не будет опубликован. Обязательные поля помечены *