Ultraviolet

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Ultraviolet (ultra-violet radiation, UVR) is light just beyond the high frequency end of the visible spectrum and progresses from the near ultraviolet to the far ultraviolet. Beyond the far ultraviolet are X-rays which are not produced by thermal radiation. It is important as exposure can be both therapeutic as in phototherapy and toxic as in sunburn and its effects on the immune system or in promoting cataract formation.

Contents

Physics

The spectrum is often divided into:

  1. Ultraviolet A (UVA, long wave, black light)
    • As used diagnostically with Wood's light and therapeutically with PUVA
    • Does contribute to indirect DNA damage so factor with malignant melanoma
    • Wavelength 400 nm – 315 nm
  2. Ultraviolet B (UVB, medium wave)
    • Allows production of vitamin D in the skin so definitely in moderation therapeutic
    • More damaging as can cause direct DNA damage, so as well as sunburn you can get the skin cancers such as squamous cell carcinoma that are associated with this.
    • Wavelength 315 nm – 280 nm
  3. Ultraviolet C (UVC, short wave)
    • Germicidal and potentially dangerous.
    • Wavelength 280 nm – 100 nm

Benefit

Can be significant as with vitamin D production, with insect screens and light sterilization and treating psoriasis.

Issues

The recommendations with regard to ultraviolet exposure have considerably tightened over the last few decades as a result of greater appreciation of its role in skin ageing and direct and indirect DNA damage leading to an epidemic of skin cancer partially mediated by over promotion of the benefits of sun exposure and inadequate precautions against sunburn. As with most radiation there is no true safety threshold and acute exposure has different consequencies to chronic exposure. There are also concerns about exposure from fluorescent lamps. At the most extreme are ultraviolet C radiators such as used in fish tank sterilization which should not be switched on in air close to the unprotected. At the other extreme are the low levels of radiation that some low energy bulbs radiate so that at 2 cm the UVR level can be equivalent to that experienced outside in the UK on a sunny day in the summer which is significant enough to need precautionary warnings[1]. Domestic fluorescent lighting does not represent a significant health hazard[2]. The use of sunbeds and sun lamps has been officially discouraged since about 2002[3].

References

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