UVA and UVB Sun protection factor

UVA and UVB Sun protection factor

UVA andUVB Sun protection factor

SPF is Sun Protection Factor. The number is determined experimentally indoors by exposing human subjects to a light spectrum meant to mimic noontime sun. The SPF number only relates to UVB protection. UVA is measured by the other definition. UVA protection is not measured through SPF numbers. 
PA is the Japanese measurement of sun protection. It is one of protection grade of UVA . UVA is based on the Persistent Pigment Darkening (PPD) reaction reading at 2-4 hours of sun exposure.  PA is a protective level of strength to mark the three PA+, PA++ and PA+++.

SPF(sun protection factor)
  • Standard: ISO 2444: 2010 cosmetic sun protection test method in vivo determination of SPF (sun protection factor)
  • Test by erythema
  • Minimal dose: MED (minimal erythema dose)
  • Process: exposure to the UV (wave length 290-400nm)
  • Test skin type: type I~ III (ITA0>280)
  • Duration: 16-24hrs after exposure

UVA-PF (UVA protection factor)
  • Standard: ISO 24442: 2011- cosmetics-sun protection test methods-in vivo determination of sunscreen UVA protection.  
  • Test by PPD (persistent pigment darkening)
  • Minimal dose: MPPDD (minimal persistent pigment darkening dose)
  • Process: exposure to the UV (wave length 320-400nm). calculate the UVA parameter by statistics.
  • Test skin type: type II~ IV (200<ITA0>410)
  • Duration: 2-4hrs after exposure

PA (Protection Grade of UVA)
PA+     = 2<UVA-PF<4
PA++    = 4<UVA-PF<8    
PA+++   = 8<UVA-PF
PA++++  = 16<UVA-PF

PA+ provides some UVA protection with a factor of PPD 2-4. It protects skin against low to medium UV radiation.
PA++ provides moderate UVA protection with a factor of PPD 4-8. It protects skin exposure to medium UV radiation.
PA+++ provides good UVA protection with a factor of PPD > 8. It is the strongest grade of UVA protection now available. It protects skin exposure under very strong or direct UV radiation.

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