Related Experiment Video
Updated: May 30, 2026

Minimal Erythema Dose (MED) Testing
Published on: May 28, 2013
Water immersion does not alter the minimal erythema dose
Michael Caswell1, Caryl Wood, Elizabeth Maly
1Consumer Product Testing Company, Inc., Fairfield, NJ 07004, USA.
Abstract:
To determine the water resistance of a sunscreen, the COLIPA method requires the determination of two minimal erythema doses (MEDs): a static MED (MED(US)) and a wet MED (MED(UW)) (1). The MED(US) is used in calculating the static SPF; the MED(UW) is used in calculating the SPF after water immersion. Herein, we report that in the 107 subjects examined, the mean MED(US) (21.0±0.55 mJ) is not different from the mean MED(UW) (21.0±0.61 mJ). This shows that water immersion does not alter the minimal erythema dose and strongly suggests that the determination of two MEDs is unnecessary and that one should be eliminated. Eliminating one of the two MED determinations would increase the benefit/risk ratio of the COLIPA sunscreen water-resistance efficacy testing without harm to efficacy.
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