14 September 2008

UV AUVA is most often associated with long term effects of photodamage and wrinkling of skin rather than the erythematous precursor of sunburn. UVA rays cause immediate and persistent tanning of the skin. While this is a suntan, it can be used as a marker for excessive UVA exposure. The method that is used most frequently is persistent pigment darkening (PPD), introduced by the Japan Cosmetic Industry Association (JCIA).

PFA = Minimal PPD (protected skin with sunscreen)

Minimal PPD (unprotected skin)
  • The determination of the protection factor for UVA (PFA-PA rated as +, ++, +++, the greater the number of +, the higher the UVA protection) was based on testing procedures proposed by JCIA.
  • Each of 10 subject’s minimal PPD dose of untreated, unprotected skin was determined by exposing test sites on the back to UVR.
  • The untreated, unprotected test area from day 0 served as the area for the minimal PPD determination on the actual test day (day1).
  • Five subsite were selected within the test site. The UVR doses selected were a geometric series representedby 1.25n, where each exposure time interval was 25% greater than the previous time. This PPD value was then used in calculating the actual PFA values.
  • The test drug and standard sunscreen control (5% avobenzone/3% octinoxate) test site were also divided into five subsites, each about 1 cm2.
  • Each of the test subsites was subjected to additional doses of UVR, determined using a geometric series of five doses, where the middle dose was placed to yield the expected PFA of the product.
  • Treated and untreated sites were examined for evidence of pigmentation at 3h after irradiation. Immediate response criteria were graded as present (1) or absent (0).
  • All sites were evaluated for PPD using the scale 0, 0.5, 1, and 2. The quantity of effective energy needed to achieve a score of 1 was considered the minimal PPD value.
  • The PFA was calculated using the minimal PPD of unprotected skin divided into the minimal PPD of protected skin. Label PFA was determined as per JCIA recommended methodology. The rating :
PA+ ---> PFA rating of <4> PFA rating of <8> PFA rating of >8

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