Ultraviolet radiation (UV radiation) is electromagnetic radiation with a wavelength below that of visible light (100 nm to 400 nm), but longer than that of X-rays. Ultraviolet means as much as beyond the violet (Ultra from lat. : beyond). Violet is the visible light with the shortest wavelength. Ultraviolet radiation is no longer perceived by the human eye.Because of the ozone layer, essentially only UVA and UVB radiation reaches the earth’s surface, with 95% of natural UV radiation in the UVA range. According to the international classification, the International Agency for Research on Cancer (IARC) assigns UV radiation of different wavelengths (UVA, UVB, UVC) to the so-called Group 1 – the group with the best evidence of carcinogenicity (cancer production). The UV index (UVI) is a normalized measure of sunburn-effective solar irradiance (ultraviolet radiation). In general, the UV index is considered to be a measure of the strongest solar irradiance around noon (peak of the day).
| UV index | Rating | Protection |
| 0-2 | low | no protection required |
| 3-5 | moderate | Protection required: headgear,t-shirt, sunglasses, sunscreen |
| 6-7 | high | Protection needed: headgear,T-shirt, sunglasses, sunscreen WHO recommends seeking shade at midday. |
| 8-10 | very high | Additional protection needed: avoid being outdoors if possible!WHO recommends avoiding being outdoors between 11 a.m. and 3 p.m.; even in the shade, sun-proof top, long pants, sunscreen, sunglasses, and a wide-brimmed hat are part of sun-safe behavior. |
| ≥ 11 | extreme | additional protection required: avoid staying outdoors if possible! WHO advises staying in the shelter of a house between 11 a.m. and 3 p.m., and outside this time, be sure to seek shade. Even in the shade, a sun-proof top, long pants, sunscreen, sunglasses and a wide-brimmed hat are considered essential. |
What is the importance of location on the intensity of UV radiation?
Depending on the location, UV rays are different in intensity, but are amplified by the weather and the environment: water reflects 5% UV radiation, sand 17%, snow 85%, even through a parasol still penetrate about 10 to 15% of the rays, grass 3%. This explains why you can get a sunburn even under a parasol. A heavily overcast sky absorbs two thirds of the radiation. Humidity also plays a special role, the drier the climate, the more intense the radiation.
What do UV-A rays do?
UV-A radiation – wavelength of 320-400 nm UV-A radiation is a long-wave, low-energy radiation that causes rapid tanning. These rays are filtered by the skin only to a small extent, which means that they penetrate deep into the skin and attack the elastic fibers (collagens). About 55% penetrate into the epidermis and about 40% into the dermis. In contrast to sunburn, the resulting cell damage (oxidative damage to DNA including double-strand breaks) is neither visible nor noticeable. For this reason, frequent exposure to UV-A radiation results in premature skin aging (skin dryness, pigment changes) and wrinkling, as well as an increased risk of skin cancer* .Studies in recent years have also shown that not only natural radiation from the sun, but also artificial light sources, such as those found in solariums (UVA high-intensity emitters), contribute to carcinogenesis (cancer development). Consistently, UV radiation has already been classified as a class 1 carcinogen by the World Health Organization (WHO).
What do UV-B rays do?
UV-B radiation – wavelength of 280-320 nm UV-B radiation is a short-wave, high-energy radiation that causes slower tanning. A large part of these rays is blocked by the horny layer of the skin. Another part penetrates into the epidermis. Due to its energy, UVB radiation is able to break down the double strands of DNA and cause lasting damage to the skin. UVB radiation is responsible for the tanning of the skin, but also for sunburn, which is dangerous to health (risk of skin cancer* ). Notice.* Sun protection for skin cancer prophylaxis, i.e. avoidance of acute and chronic UV damage – because of actinic keratosis (cancer precursor; risk factor for squamous cell carcinoma), squamous cell carcinoma of the skin, basal cell carcinoma (BZK; basal cell carcinoma; 10 times more frequent than malignant melanoma), malignant melanoma.
An important biological significance of UVB radiation is the formation of calciferol (vitamin D3) from cholesterol in the skin. It has the function of a prohormone in the body and is converted via an intermediate stage to the hormone calcitriol. The vitamin D system has essential autocrine functions in a wide variety of tissues:
- Cell differentiation
- Inhibition of cell proliferation
- Apoptosis (programmed cell death)
- Immunomodulation
- Control of other hormonal systems
Vitamin D deficiency is an independent risk factor for:
- Autoimmune diseases (such as type 1 diabetes mellitus, Crohn’s disease, multiple sclerosis (MS), systemic lupus erythematosus, SLE).
- Skin diseases such as psoriasis (psoriasis).
- Infectious diseases such as tuberculosis
- Hypertension (high blood pressure)
Furthermore, it is considered that vitamin D and calcium is protective with respect to colon cancer (colon carcinoma).
What do UV-C rays?
UV-C radiation – wavelength of 200-280 nm UV-C radiation is a very short-wave, high-energy radiation. It is practically completely absorbed by keratinized skin already at the surface and is therefore less effective in damaging deeper cell layers than UV-B light, which is absorbed more weakly and thus penetrates to the deeper cell layers. The biological effect of UV-C rays is to damage nucleic acids. The best-known representative of nucleic acids is deoxyribonucleic acid (DNA), the storehouse of genetic information. In addition to their role as information stores, nucleic acids can also serve as messengers (signal transducers) or catalyze biochemical reactions.
