title: The sun--our friend or foe?
abstract: OBJECTIVE
  Sunlight is the major source of the energy on Earth. Visible light, ultraviolet and infrared radiation are necessary to sustain life on our planet. However, besides the range of positive effects, such as photosynthesis in plants, warmth, vision, and synthesis of vitamin D, sunlight may also be responsible for negative biologic effects - sunburn, induction of photodermatoses or carcinogenesis. Ultraviolet is regarded as the major environmental, physical hazard to the human skin.
  The acute clinical effect of ultraviolet involves melanogenesis, i.e. tanning, which protects from sunburn if exposure is overdosed. A single exposure, as well as acute suberythemal irradiation, suppresses sensitization of the contact hypersensitivity. The chronic biological effects are photoageing and skin cancer, especially squamous cell carcinoma (SCC). Vitamin D synthesis is regarded as a benefit of natural acute and chronic exposure to ultraviolet. Ultraviolet also plays an important role in aetiology of the group of disorders characterized by photosensitivity. On the other hand ultraviolet is a known inducer of immunosuppression in the skin; therefore, phototherapy is a therapeutic option for patients with activation of dermal immunity.
  
  
  CONCLUSIONS
  Without sunlight, the existence of life on Earth is not possible. On the other hand, UVR radiation is regarded as representing one of the most important environmental hazards for human skin. For a better understanding of the mechanisms related to the influence of UVR on human skin, and the most dangerous chronic effects of carcinogenesis, it is necessary to undertake some protective activities. Moreover, UVR may become our ally in the treatment of selected skin disorders.
authors: Department of Dermatology, University of Medical Sciences, Poznan, Poland. agnieszka.osmola@wp.pl
authors: Agnieszka
authors: A
authors: Osmola-Mańkowska
authors: Wojciech
authors: W
authors: Silny
authors: Aleksandra
authors: A
authors: Dańczak-Pazdrowska
authors: Karolina
authors: K
authors: Olek-Hrab
authors: Bartosz
authors: B
authors: Mańkowski
authors: Krzysztof
authors: K
authors: Osmola
authors: Dorota
authors: D
authors: Hojan-Jezierska
authors: Leszek
authors: L
authors: Kubisz
mesh_terms: D006801:Humans; D010789:Phototherapy / Q000009:adverse effects; D012867:Skin / Q000528:radiation effects*; D012871:Skin Diseases / Q000209:etiology* / Q000473:pathology / Q000503:physiopathology / Q000517:prevention & control; D012879:Skin Physiological Phenomena / Q000528:radiation effects*; D013472:Sunlight / Q000009:adverse effects*; D014807:Vitamin D / Q000096:biosynthesis / Q000528:radiation effects
chemical_list: D014807:Vitamin D