The light as regards the bodies that receive it can behave of three ways: it can be reflected, transmitted or absorbed across the body on which it affects. Only the absorbed light will develop his energy and will have, therefore, some photobiological effect.
These effects are realized on a cromóforo that is a molecule capable of absorbing the light.

Our ambience is formed by two concentric air layers: the immediate one to the Earth named Troposfera, with a thickness of approximately 15.000 meters and on the outside of her, wrapping it, the Stratosphere from 15.000 meters to 50.000 meters. The Stratosphere realizes the fundamental filter function, absorbing almost the totality of the UVC and enclosed report of the radiations of minor wavelength of the UVB, but without any action on the GRAPE. The principal cromóforo for it is the system oxygen - ozone.

The called ozone layer is not a real layer since the ozone is dispersed in the immensity of the stratosphere in very small proportions, 10 parts for million, I hold also to form and to decompose continuously.
From the decade of 1970 one begins detecting a reduction of the proportions of the stratospheric ozone, especially in the Antarctic. Such reductions would not be explained only by the natural cycles and one found that between the possible causes it might be for the action of the compounds halogenados spilled in the ambience corresponding to the group of the clorofluorocarbonados, short chains of carbon containing chlorine and fluorine. The chlorine destroys the ozone in a catalytic reaction in which that one does not wear out. To this he adds to himself that the clorofluocarbonados are very stable, with an average life from 75 to 120 years, with what only one radical chlorine in the stratosphere is capable of destroying 100.000 ozone molecules.

At present the industry has carried out a drastic reduction of these compounds used as propellents of sprays and refrigeration, replacing them with other gases. The consequences of a theoretical disappearance of the ozone would be catastrophic for the life in the Earth, but it is necessary to warn several attenuants: an entire disappearance of the ozone is not easy, since his source is the oxygen; although there were important ozone reductions, there would stay a minimum that might be sufficient to leak the UVC, although yes it might increase the proportion of UVB of short wavelengths, with what the aggressiveness of the light of the Sun would be major. The effects of the loss of ozone are not sufficiently clear, we cannot know if the composition of the light that comes to us is different from that of hace fifty or more years since it was not measured. The problem will clear up in the next years.

The solar light produces infrared beams (heat), visible light (color), ultraviolet (GRAPE, UVB) that there produce the bronze-colored one and the cellular changes that they predispose to the cancer. This radiation is major between 10 of the morning and 4 p.m. At these hours the level of radiations UV is major and more aggressive and carcinogenic. For it we should sunbathe out of these hours.
The bronze-colored one is a mechanism of defense of the skin, since he exercises an effect of filter of beams UV. The exhibition to the sun in normal skins must be realized increasing 10 minutes of exhibition every day, from the first one that must not exceed 15 minutes, avoiding the hours of the midday. To 10 days the skin will be prepared to support the sun without problems except those of accumulation of solar radiation (important to prepare the leather cancer).

It is necessary to bear in mind that type of skin has each one, red-haired and fair-haired are had by very little aptitude to tolerate the solar radiation, the chestnut-trees can be considered to be normal, and those of dark skin tolerate major speed in the capture of the sun.
The factors of solar protection only offer an increase in the tolerance time to the solar beams (especially for beams UVB), but in fact they can allow to take a normal life.
They are demonstrated useless in wide bogeys of action and to leak beams GRAPE and visible light (except the filters of entire physical screen by means of titanium dioxide. The protection factors must apply 30-45 minutes to themselves before the exhibition begins to the sun, being eliminated by the perspiration and the water.

The protection indexes are the factor for which it is necessary to multiply to know how long it protects us, example: A protection factor 20 allows to exhibit to the sun 20 minutes as if 1 minute was alone. The filter 50 allows 50 minutes as if it was 1. We will be able to find filters from factor 2 up to factor 50 or more that they are called entire or screens.
It is necessary to bear in mind that the water increases at least 10 % the absorbed beams, it does an effect magnifying glass, in addition to which it sweeps the effect of the solar protectors.
As well as the clouds leak the infrared beams and those of visible light but not the UV, for it the apparent protection effect is an enemy, it is not hot so... and it is not like that. The clear surfaces, sand, snow are very reflecting and they increase the solar radiation, taken care.

The photosensibility reactions ó lucitis can split in:

• Solar hives
• Light polymorphous eruption.
• Photopoisonous reactions, aspect of intense solar burn, eritema, blister, increase of color of the skin.
• Photoallergic reactions, with formation of hives, eczema or other forms of cutaneous reaction.
• Other reactions produced by illnesses aggravated by the sun (lupus eritematoso systemic, simple herpes, rosy, eritema multiform, pénfigo, etc.) edema and bustles. For example, porfiria cutaneous it is late or fitofotodermatitis.

The treatment is by means of antiallergic, cortisone, antimaláricos, betacaroteno, used alone or in combination depending on the cases.

• Go out outdoors only before 9 a.m. and after 4 p.m.
• Use clothes and a hat of wide wings that does not allow the penetration of the light
• Avoid the exhibition prolonged to the fluorescent lamps
• Protect his face and hands with the highest solar protection factor that finds.
• Use sunglasses
• Do not enjoy speaking with his friends in the street
• Place opaque protections to the ultraviolet beams in the glazing of his car
• Use solar filters

TO SEE ALSO

• Leather cancer
• Exanthemas for the Sun

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