Water immersion does not alter the minimal erythema dose

Area of Science:

• Dermatology
• Photobiology
• Cosmetic Science

Background:

• The COLIPA method for sunscreen water resistance involves measuring two minimal erythema doses (MEDs): static (MED(US)) and wet (MED(UW)).
• MED(US) is used for static Sun Protection Factor (SPF) calculation, while MED(UW) is used for SPF determination after water immersion.

Purpose of the Study:

• To evaluate the necessity of determining both static and wet minimal erythema doses (MEDs) in sunscreen water resistance testing.
• To determine if water immersion significantly alters the minimal erythema dose (MED) required for sunscreen efficacy assessment.

Main Methods:

• The study involved 107 human subjects to assess sunscreen water resistance.
• Two minimal erythema doses (MEDs) were determined: a static MED (MED(US)) and a wet MED (MED(UW)) following the COLIPA method.

Main Results:

• The mean static MED (MED(US)) was 21.0±0.55 mJ.
• The mean wet MED (MED(UW)) was 21.0±0.61 mJ.
• No statistically significant difference was observed between the mean MED(US) and mean MED(UW).

Conclusions:

• Water immersion does not alter the minimal erythema dose (MED).
• The determination of two separate MEDs (static and wet) in the COLIPA method is redundant.
• Eliminating one MED determination would streamline sunscreen water resistance testing without compromising efficacy, improving the benefit/risk ratio.