White, brown or red?

For many people summer is synonymous of beach and tan. But there are people who are not tan during winter. Some people prefer to use UVA tanning booths a few months before, and others take the sun without protection to catch some colour. What consequences can this have? Then I will talk about the skin and the effect of radiation on it.

OUR SKIN

The skin is the largest organ of our body, has an area between 1.5 and 2m2 of surface and a weight around 3.5-5kg. Their functions are:

  • Protection: protects the internal organs from trauma and prevents the loss of water and electrolytes from the inside.
  • Thermoregulation: the blood vessels increase or decrease the temperature of the skin. When it is very hot the sweat refreshes the skin surface.
  • Sensitivity: the perception of touch, pressure, temperature, pain and itching is done through the skin.
  • Secretion: the skin protects the body from dehydration.
  • Excretion: through the skin we eliminate about 350ml per day of water, which we have to recover by moisturizing. In certain diseases you can get rid of a lot of protein and sulfur.

The skin has two basic cells: keratinocytes (80%) and melanocytes (10%). The melanin, which gives the tan, is found inside the melanocytes and accumulates in some bags (melanosomes). When it does not touch the light it remains in deep strata, whereas when it touches the sun goes up by the keratinocytes (Figure 1).

melanocitos
Figure 1. Melanin (arrows) rising towards the keratinocytes (Source: Salud del Siglo XXI)

Tan is the synthesis of new melanin. Not all people produce the same amount of melanin. We all have the same number of melanocytes, but the difference is in the number of melanosomes.

Our skin is formed by 3 layers that are, ordered from superior to inferior, epidermis, dermis and hypodermis (Figure 2).

capes pell
Figure 2. Skin layers: A) epidermis, B) dermis and C) hypodermis (Source: MedlinePlus)

The tanning process passes into epidermis, which is the top layer of the skin. Epidermis is 0.2mm thick and subdivided into 4 or 5 layers, depending on the body part. For example, the palms of the hands and soles of the feet are formed by 5 layers, where the extra layer gives more resistance. The thickness of the skin in these areas is 1-2mm, in contrast, in other areas, as in the eyelids, is lower (0.004mm). In the inner or deep layers, the cells are younger and more active, and along the cycle, they ascend to the outer or superficial area, becoming dead cells, without nucli and formed basically by keratin (dead skin).

Below, there is dermis that gives elasticity to the skin, where you find the nerves and blood vessels and is where the hairs and nails grow. Finally, hypodermis is below everything and is where the glands are.

RADIATION FROM OUR SKIN

The sun emits radiation with wavelengths ranging from 0.1 to 17,000nm. But only the radiations between 280 and 3,000nm arrive to the Earth (the others remain in the ozone layer).

Radiation that affects living organisms involves spectrum of 280-800nm (UVB, UVA, visible light and a part of infrared) (Figure 3).

e
Figure 3. Electromagnetic spectrum (Source: J. E. Martin Cordero. Agentes Físicos Terapéuticos (2009))

Not all radiation penetrates in the same way on our skin. Table 1 shows the level of penetration:

Table 1. Penetration according to the different radiation.

Type

Wavelenght

Level of penetration

Ultraviolet

UVC

100-280nm

UVB

280-315nm

Epidermis

UVA

315-400nm

Dermis

Visible light

VL

400-700nm

Dermis

Infrared IR >700nm

Hypodermis

It is important to know that prolonged exposure, without taking precautions, can not only produce skin cancer, but can also have other effects. UVB radiation is the most common cause of sunburn, erythema or redness. It is also the most common cause of skin cancer. In contrast, UVA radiation rarely causes burns, but is responsible for most photosensitization (abnormal increase in skin sensitivity to UV radiation) and may be carcinogenic in the presence of certain substances that enhance its effect. In addition, it causes aging of the skin (Figure 4).

In tanning booths 30% of the radiation is UV. Mostly it is UVA radiation, but there is also UVB radiation (albeit to a lesser extent). The remaining percentage is infrared radiation and visible light.

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Figure 4. UVA (aging) and UVB radiation (burns) effects (Source: Antirughe.info)

The amount of irradiation is greater when the more near is the Earth of the Sun (zone of the Equator, between the Tropics of Cancer and Capricorn, or between 12 and 16 hours). This irradiation can damage our DNA, causing breaks in the DNA strand that can cause mutations.

UV rays easily pass through clouds and water vapor, but are partially absorbed by atmospheric pollution. It has been seen that in areas where there are holes in the ozone layer the incidence of skin cancer is higher. This is because the damage caused in the ozone layer allows the passage of more amount of UVB rays. Here the importance of not damaging the ozone layer, as it protects us from these rays.

WE NEED TO PROTECT OUR SKIN

Since the light can be reflected by several substances, it is necessary to take into account that, to direct rays of the sun, can be added those that arrive tangentially on a bright day and that are reflected by sand, water, soil, gel, snow…

Radiation doses are cumulative and may add to the effects of ionizing radiation (X-rays). The presence of skin cancer can be observed many years after an acute burn. This has been observed in American sailors who were in the Pacific during World War II, and who were exposed for months or years to high intensity solar radiation. These sailors have developed over the years different types of skin cancer.

For this reason it is very important to take the correct sun protection measures: use photoprotectors, avoid long periods in the sun, especially in hours of maximum solar intensity; and moisturize often.

REFERENCES

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