Solar radiation spans the wavelengths between 200 and 4000 nm and includes ultraviolet, visible and infrared radiation.
UVB 290-320nm, UVA 320-400nm.
Ultraviolet wavelengths are 100 to 400 nanometres (nm, billionths of a meter) and are divided into three bands: A, B and C.
UVA wavelengths are the longest, 315 to 400 nm; UVB are 280 to 315 nm, and UVC wavelengths are the shortest, 100 to 280 nm.
Ultraviolet radiation (UVR) is part of the electromagnetic spectrum, just beyond visible light.
UVA associated with tanning, skin aging and skin cancers.
UVA accounts for 95% of sun’s radiation with UVB making up the majority of the remainder.
UVA rays have longer wavelengths and can deeply penetrate the dermis.
The rays damage existing collagen, which causes increased elastin production.
UVA exposure,causes fine lines and wrinkles around the eyes, mouth, and forehead, as well as age spots, sometimes called liver spots.
The adverse effects of ultraviolet radiation are the cellular generation of reactive oxygen species, damage to lipid bilayers, and cellular macromolecules such as DNA, and immune suppression.
About 95% of the UVR that reaches the earth from the sun is UVA and 5% UVB;, while no appreciable UVC reaches the earth.
Due to the presence of blood vessels in the dermis, UVA rays can lead to dilated or broken blood vessels which are most commonly visible on the nose and cheeks.
UVA can also damage DNA indirectly through the generation of reactive oxygen species (ROS), which include superoxide anion, peroxide and singlet oxygen.
ROS damage cellular DNA as well as lipids and proteins.
UV exposure can also lead to inflammation and vasodilation which is clinically manifested as sunburn.
UVA and UVB radiation are carcinogenic, inducing DNA double stranded breaks and formation of cyclobutane pyrimidine dimer and pyrimidine photoproducts, respectively.
UVB associated with sunburns and skin cancers.
UVB much more important in the induction of skin cancer and actinic keratoses than UVA.
In general, UVB rays burn, while UVA rays age the skin, but there is considerable overlap in the damage these rays cause.
UVR causes local and systemic immunosuppression, a potential underlying mechanism for the development of skin cancer.
UV radiation is the most important known modifiable risk factor for the development of skin cancer including melanoma.
Whole exam sequencing of primary and metastatic melanoma find 76% of primary melanomas and 84% of metastatic melanomas have an ultraviolet signature mutation.
UV of pain from indoor tanning equipment is similar to or exceeds the dose of radiation typically received from the sun over any similar period of time, character of the radiation is similar.
The demographic group with the heaviest exposure to indoor UV tanning is a young women, a group with an increase in the incidence of melanoma.
It is suggested that the widespread use of indoor UV by teenage girls and young women will have important public health consequences.
Ambient UV radiation exposure is associated with a higher risk of HZ in men but not in women.
A history of severe sunburn is associated with a modest increase in risk of HZ in men and women, possibly because of immunosuppression from over exposure to the sun (Kawai K).
In transplant recipients high UVR is associated with increased risk of reactivation of varicella virus and herpes simplex virus.
To reduce UVR measures include: seeking shade, wearing hats and protective clothing, avoiding outdoor activities during peak sunlight hours, and regularly using sunscreen.