The relation between sun protection factor and amount of suncreen applied in vivo

@article{Faurschou2007TheRB,
  title={The relation between sun protection factor and amount of suncreen applied in vivo},
  author={Annesofie Faurschou and Hans Christian Wulf},
  journal={British Journal of Dermatology},
  year={2007},
  volume={156}
}
Background  The declared sun protection factor (SPF) is based on the use of a sunscreen layer of 2 mg cm−2. However, only around a quarter (0·5 mg cm−2) of this amount is applied by sunbathers. Theoretical calculations have suggested that the effective SPF is related to sunscreen quantity in an exponential way but this was not confirmed in vitro and has not been studied in vivo. 
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People typically apply around 0·8 mg cm−2 and use sunscreen daily for holidays and such use results in erythema, which is a risk factor for skin cancer.
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