beauty

Tan and Ultraviolet rays

The sun

In addition to the well-known ultraviolet rays responsible for tanning, the sun emits a large quantity and variety of electromagnetic radiations that originate from the thermonuclear reactions that take place at the level of its nucleus.

Fortunately, solar radiation is largely absorbed by the earth's atmosphere which acts as a real filter. If it were not so, life would probably not exist on Earth, or at least, not as we know it today.

However, the radiations that manage to cross this natural protective barrier are composed of three different types of light:

  • The one visible to the naked eye ranging from red to violet;
  • The infrared (ie, below the frequency of the red that is visible to the human eye), is an invisible radiation, but perceptible in the form of heat;
  • The ultraviolet one (ie, which lies beyond the frequency of the violet visible to the human eye). This radiation, with its different wavelengths, is the cause of the much sought-after tan.

The effects of these types of light on the organism are variable, just as the mode of absorption is different.

Types of Light

As mentioned, the electromagnetic radiations produced by the sun and able to cross the barrier formed by the earth's atmosphere are of three types: visible, infrared and UV.

The main characteristics of these types of light will be briefly described below.

Visible light

Visible light represents about 37% of the electromagnetic radiation that exceeds the atmosphere. It is not dangerous to health and does not attack the skin, but can sometimes cause irritating glare to the eyes.

Light is very important for the regulation of certain bodily activities such as the wake sleep cycle and the circadian pattern of hormones. It is also able to stimulate the production of serotonin, an important neurotransmitter, responsible, among other things, for a sense of euphoria.

Infrared rays

Infrared rays make up about 60% of the radiation that reaches the Earth beyond the atmosphere. For thermal effects that determine, they are artificially reproduced and used for therapeutic purposes. Their most important feature is the transmission of heat to the surface layer of the skin (stratum corneum). Therefore, excessive absorption can damage the skin due to hyperthermia and cause symptoms ranging from vasodilation to skin dehydration.

UV rays

UV rays are those that reach the Earth in less quantity (about 3%), but not for this reason they are less important, indeed, as we will see in the next paragraph, they can be as useful to our body as they are harmful.

Most UV rays are reflected by the superficial horny layer and only a small amount reaches the deeper layers of the epidermis. Depending on the wavelength, they are divided into UV-A, UV-B and UV-C.

Their most important feature is the wavelength that determines the depth of skin penetration.

Ultraviolet rays

Ultraviolet rays can in turn be classified into three groups according to the wavelength they possess.

We can therefore distinguish:

  • UV-A rays , represent about 98% of the UV rays that hit the Earth and have a wavelength of 320 - 400 nm.

    UV-A, have excellent effects on tanning (even if lower than UV-B) and moderate on skin damage.

    Given their high wavelength they are nevertheless able to penetrate deep into the dermis destroying capillaries, collagen and elastin, causing erythema and damaging the skin, even in the long term.

  • UV-B rays, constitute 2% of the ultraviolet radiation that exceeds the atmosphere and have a wavelength of 280 - 320 nm.

    UV-B rays have a lower penetration capacity and cannot overcome the more superficial structures of the skin. The deleterious effects are however important because the UV-B rays are able to alter the genetic material contained in the DNA increasing the risk of appearance of skin tumors.

    UV-B radiation is much more effective than UV-A radiation in causing erythema.

  • UV-C rays, are the most dangerous ultraviolet rays and have a wavelength of 100 - 280 nm. UV-C rays are particularly harmful to health because they have a high carcinogenic power. Fortunately, they are retained by the ozone layer and therefore have no particular effects on the skin.

    The risk of exposure to these rays increases at high altitude.

Did you know that ...

While it is true that UV rays can cause various damages to the skin and the body more generally, on the other hand it is also true that ultraviolet radiations are necessary for carrying out some physiological processes and can bring various benefits.

In fact, ultraviolet rays:

  • They promote trophism and bone growth by stimulating the synthesis of vitamin D;
  • They perform a disinfectant action at the level of the skin;
  • They promote circulation and consequently stimulate the activity of white blood cells;
  • They accelerate the piliferous proliferation (perhaps this effect is not fully appreciated, especially by women);
  • They promote the pigmentation of the skin by stimulating the production of melanin (in truth, this is a defense mechanism implemented by the body to protect cells from possible UV rays damage; however, nowadays, a tan is considered a synonym of beauty and for this, skin browning is a much sought after factor).

Sun damage

Although ultraviolet rays can, at least in part, be considered useful for the body, excessive and uncontrolled exposure leads to the inevitable occurrence of undesirable effects and the appearance of various types of damage that can occur both in the short and in the long term. Among the most serious damages we find without a doubt skin tumors. On the other hand, skin discolouration (sun spots), wrinkles or sunburn are less serious.

Erythema is nothing but the classic sunburn that occurs with common symptoms: rupture of small vessels, blisters, edema, peeling, leakage of fluid and skin aging in general (structural sagging, wrinkles, etc.). Responsible for these effects is local hyperthermia caused by the absorption of heat transmitted by UV rays.