UV radiation and its effect
Science divides sunlight into different wavelength sections. In this respect, the short-wave energy-rich ultraviolet radiation has the most severe effect on human health.
Apart from the visible light (780 - 400 nm) and the more long-wave infrared radiation there is also the more short-wave, more energy-rich ultraviolet radiation (400-100 nm, nm= nanometre). Within ultraviolet radiation one differentiates in analogy to their different effects on organisms between UV-A radiation (400-315 nm), UV-B radiation (315-280 nm) and the most energy-rich UV-C radiation (280-100 nm). Whereas the UV-C radiation is completely absorbed by the atmosphere, about 10 % of the UV-B radiation and the most part of the UV-A radiation pierces through to the earth’s surface.
Neither can humans – as opposed to some insects for example – see in the UV range, nor can they perceive UV radiation with any other sensory organ, as opposed to the infrared radiation of the sun, which humans cannot see either, but feel as heat on the skin.
This is exactly why UV radiation can become dangerous. If, in the case of intensive sun radiation, the heat sensation disappears, for example due to slight wind, you quite easily forget about the effect of the persistently effective UV radiation.
Effects on Humans
Moderate UV radiation has also positive effects on humans. UV radiation is necessary for the formation of vitamin D3 in human organisms; however, for this purpose mild sunlight for considerably less than one hour per day is sufficient.
However, due to the changed leisure time behaviour in the course of the past few decades people have become more and more aware of the harmful effects on excessive UV radiation.
The most well-known acute harmful effect is sunburn; in this case inflammatory reactions lead to erythema and itching.
On the long run, frequent exposure to UV radiation results in premature skin aging. In the course of this process, the skin loses its elasticity, which results in the formation of wrinkles and in a damage to the connective tissue. As to premature skin aging UV-A radiation plays a considerable role.
As the most dangerous consequence of UB radiation, skin cancer is to be mentioned. A clear correlation between exposure to UV radiation and the frequency of the occurrence of cases of cancer exists with basalioma and spinalioma. Even if the mortality rate is very low the therapy of these carcinoma especially occurring in the face, on the scalp, and on the forearm can be problematic from the cosmetic point of view.
The malignant melanoma constitutes a special danger, for which there are only good chances of healing in case of early detection. Frequent sunburns in childhood and youth are considered to be risk factors; in general, there seems to be a correlation between the frequency of melanomas and frequently recurring exposure to UV radiation.
However, it is not only sunlight that contains a share of UV radiation. In addition, artificial light sources can emit UV radiation. In this context solariums, which are used for cosmetic purposes, have the most severe effects on human health.
The eye, too, reacts on UV radiation. Very high radiation can lead acutely to conjunctivitis, corneal inflammation and, in extreme cases even to snow blindness. Such diseases are painful, but they heal up without leaving permanent damage.
However, on the long run UV radiation increases the probability for the occurrence of cataract.
It is also assumed that the UV radiation can weaken the human immune system. This increases the vulnerability for all kinds of infections.