Beauty

There are also products that make it possible to quickly and easily get an even tan, and even those that make dark skin lighter.

Today, moderately tanned skin is considered the most beautiful. It is still accepted that such a tan speaks of the health of its owner and is considered unconditionally attractive. Most people sunbathe during their holidays, and they tend to go to places where the sun shines almost all day, so they often choose the Mediterranean or Caribbean coasts, Australia, Southeast Asia, California and Florida for their holidays. But by doing so, they not only put themselves at risk of getting skin cancer, but they also get skin damage that does not heal for a long time, which ultimately leads to violations of its texture and the appearance of the so-called chapped skin. Ultraviolet rays, namely ultraviolet B rays, are to blame for all this. These rays can penetrate deep into the skin and cause cancer by damaging nuclear DNA and suppressing the immune system.

Visible light is made up of six spectral colors that are easily visible to the eye: red, orange, yellow, green, blue and violet. Red corresponds to wavelengths from 740 to 620 nanometers (nm), orange — from 620 to 585 nm, yellow — 585-575 nm, green — 575-500 nm, blue — 500-445 nm and violet — 445-400 nm. The human eye does not perceive light with a wavelength shorter than 400 nm, followed by waves with a wavelength of 400-320 nm, called ultraviolet A, and further with a wavelength of 320-280 nm, which are called ultraviolet B. A large proportion of the rays of this invisible part of the spectrum do not reach to the Earth’s surface, because in the upper atmosphere they are absorbed by ozone.

Although we can’t see either UVA or UVB, these rays can invisibly damage our eyes and affect our skin: under UVA, the skin gradually turns brown, while under UVB, the process is much faster, and the skin takes on a fiery red color. UV-A is sometimes called aging rays due to their ability to accelerate skin aging, and UV-B is called scorching rays, as they dilate the blood vessels of the integumentary tissues and increase their blood supply, which leads to an increase in skin temperature and redness.

Human skin cells themselves are colorless, but in the process of evolution they have developed a mechanism for protection against sunlight, which is based on the formation of special molecules. These molecules can be found in the superficial layer of the skin, the epidermis, and are capable of absorbing ultraviolet rays. Most defense molecules are amino acids such as tryptophan and tyrosine, plus urocanic acid, which is synthesized from the amino acid histidine. Urocanic acid has the ability to suppress the immune system, and this, of course, cannot please us. Once the immunosuppressive (immune suppressive) effect of urocanic acid was discovered, it was first added to cosmetics as a moisturizing agent, and in the sixties it became known about the sunscreen properties of this substance. But now the use of urocanic acid in cosmetic preparations is prohibited.

The most effective natural UV filter is the pigment melanin, which is produced in the upper layers of the skin by special cells called melanocytes. (Melanin gives dark color to hair, feathers, and fur.) Cells begin to produce this pigment when exposed to UV-A rays, while synthesizing it from the amino acid tyrosine. Tyrosine molecules bind to each other and form the melanin polymer.

The more UV-A that hits the skin, the more melanin is produced and the darker the skin becomes. Some organisms also use melanin to protect themselves from the sun, including almost all types of mammals, insects, some plants, fungi, and even bacteria. Africans already at birth have a high level of melanin, this level is maintained throughout their lives. Fair-skinned people need time for melanin to develop, so when exposed to the sun, they have little protection against ultraviolet radiation at first.

All representatives of our species are divided into four groups according to skin type. The first group is most susceptible to sunburn, the fourth group is the least sensitive. The ancestors of the Celts, now living in Northern Europe, belong to the first and second types, they are most susceptible to sunburn, they do not manage to tan well, because their body is not capable of intensive production of melanin. At the same time, people whose ancestors inhabited the Mediterranean belong to the third and fourth types, they quickly tan and rarely burn in the sun. Red-haired people burn easily in the sun, despite the fact that their skin produces melanin, but their pigment is not able to create full protection.

Some people have so few melanocytes that their skin becomes hot and red when exposed to the sun, so people need to wear artificial sun protection regularly if they want to go outside. Such individuals are called photosensitive. Photosensitivity can develop as a side effect of certain medications.

Sunscreens. Part 2

Sunscreens. Part 3

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

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