UVB rays

Ultraviolet radiation Invisible rays that are part of the energy that comes from the sun. UV radiation can damage the skin and cause melanoma and other types of skin cancer. UV radiation that reaches the earth s surface is made up of two types of rays, called UVA and UVB rays. UVB rays are more likely than UVA rays to cause sunburn, but UVA rays pass deeper into the skin. Scientists have long thought that UVB radiation can cause melanoma and other types of skin cancer. They now think that UVA radiation also may add to skin damage that can lead to skin cancer and cause premature aging. For this reason, skin specialists recommend that people use sunscreens that reflect, absorb, or scatter both kinds of UV radiation. [NIH]... 

Sunscreen preparations tend to contain substances that protect the skin against sunburn caused by ultraviolet B (UVB) rays. UVA rays are associated v/ith long-term skin damage. Sunscreen preparations contain a variety of sun protection factors but not necessarily a factor of 30. 

Cejkova, J., Stipek, S., Crkovska, J., Ardan, T. Changes of superoxide dismutase, catalase and glutathione peroxidase in the corneal epithelium after UVB rays. Histochemical and biochemical study. Histol Histopathol 15(4), 1043-1050... 

Solar UV rays are classified into three groups UVA rays have the longest wavelength and account for 90% of the total UVB rays have higher energy and are the most damaging UVC rays are filtered out by the ozone layer. 

The Sun Protection Factor (SPF) is the ratio of the amount of UVB radiation that is just enough to produce sunburn on protected skin to the amount that will produce the same effect on unprotected skin. For example, skin protected by a sunscreen with an SPF of 10 should be able to withstand a given intensity of UVB rays for 10 times as long as unprotected skin before burning. As no assessment of UVA protection is included, the SPF should not be used as the basis for recommending a sunscreen to a patient who is sensitive to UVA. 

The UV photons that have not been reflected or absorbed reach the basal layer of the epidermis, the papillary dermis and the reticular dermis. UVA rays that are emitted perpendicular to the skin penetrate deeply 66% get through the stratum corneum and 44% reach the basal layer. They have relatively little effect on the epidermis, but do severe damage to the dermis. Some 17% of UVB rays get through the stratum corneum and 3% reach the basal layer. They cause more damage to the epidermis than to the dermis. The thickness of the stratum corneum is therefore an important part of the skin s defenses, and treatments that damage it (dermabrasion, laser, AHA creams, peels, etc.) allow photons in and promote the free-radical damage described above. 

Wastewater treatment may also require the use of UVA-UVB rays as a mechanism to kill any unwanted cellular material. Unsparged photoelectrochemical... 

Gienerously apply sunscreen — Use about one ounce to cover all exposed skin 20 minutes before going outside. Simscreen shoidd have a Sim Protection Factor (SPF) of at least 15 and provide protection from both ultraviolet A (UVA) and ultraviolet B (UVB) rays. Reapply every two hours, even on cloudy days, and after sweating, following the apphcation directions on the bottle or tube. 

The association of facial creams with face shield can strengthen the protective barrier against chemical splash, moisturize, block UVA and UVB rays, and prevent dermatitis. 

UV radiation from the Sun that impinges upon the Earth s surface is in wavelengths between 290 and 400 nm. The UV rays that reach the Earth are classified as UVA (long length waves of 320-400 nm) and UVB (short length waves of 290-320 nm). 

People who use tretinoin often report that their skin is more sensitive to the sun and burns more easily. This photosensitization is better explained by the thinning of the stratum corneum rather than by a photochemical reaction between the tretinoin and the sun s rays. It is therefore essential to recommend the use of a sunscreen (SPF 25-50 UVA + UVB + HSP induction) to patients being treated with tretinoin. It should also be borne in mind that there is a potential risk of skin cancers developing as a result of the stratum corneum thinning and the enhanced penetration of the sun s rays. Nevertheless, it appears that patients on longterm tretinoin treatment do not have a higher incidence of skin cancers. Tretinoin has in fact proved to be effective in the treatment of photoaging and actinic keratoses. 

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UV rays derived from the skin induce an increased incidence of all skin cancers, including squamous cell carcinoma, basal cell carcinoma, and malignant melanoma of the skin. The wavelength of UV light most associated with skin cancer is UVB (280-320 nm), which forms pyrimidine dimers in DNA. This type of DNA damage is repaired by nucleotide excision repair pathways that require products of at least 20 genes. With excessive exposure to the sun, the nucleotide excision repair pathway is overwhelmed, and some damage remains unrepaired. 

Lin L-R, Chen SC, Reddy VN, Giblin FJ. Green tea polyphenols protect against H202, UVB and X-ray induced damage in cultured dog lens epithelial cells. Exp Eye Res 1998 67 S141. 

Precautions No sunscreen can completely block out the sun s damaging rays. Therefore, it is necessary to limit exposure and reapply after swimming and exercise. The sun s two ultraviolet rays UVA and UVB. UVA primarily causes premature aging and wrinkling UVB primarily causes sunburn and skin cancer, although both can cause aging and cancer. 

These PISs can initiate the photopolymerization of synthetic, as well as renewable, monomers/oligomers. A careful adaptation of the PISs to novel light sources avoiding the harmful mercury lamps emitting UVA and UVB or even UVC rays has been possible, and today, polychromatic visible light irradiation devices (Xe, Hg-Xe and doped lamps), quasi-monochromatic devices (LED arrangements) or monochromatic devices (laser diode arrays) can be safely used. 

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