Minimal erythema dose, minimal persistent pigment dose which model for whitening products evaluation is better?

Background/aims: How to select a suitable method in whitening products evaluation is still under discussion. Here, we compared two different artificial pigmentation models and explored an ideal UV dosage for skin whitening products evaluation model establishment.

Methods: Thirty five healthy volunteers with type IV human skin were recruited and the skin minimal erythema dose (MEDs) and minimal persistent pigment dose (MPPDs) were measured. All volunteers were simultaneously exposed to six increasing doses of radiations from different ultraviolet sources on lower back bilateral flattening area: 95% UVA/5% UVB with the radiating doses of 0.75, 0.94, 1.17, 1.46, 1.83, 2.29 MEDs was used on the left side; meanwhile 99% UVA/1% UVB with radiating doses of 6.0, 7.5, 9.4, 11.7, 14.6, 18.3 MPPDs were used on the right side. Observations and pigmentation measurements were carried out before and after UV radiation for 24 weeks.

Result: 1.83 MED and 2.29 MED induced medium depth pigmentation by 95% UVA/5% UVB irradiation. 1.83 MED dose causing minimal photo-damage on skin was selected as the most suitable dose. With 99% UVA/1% UVB irradiation, 9.4 MPPD and 11.7 MPPD induced medium depth pigmentation. 9.4 MPPD dose causing minimal photo-damage on skin was selected.

Conclusion: These findings potentiate advanced understanding of UV model establishment and selection for skin whitening products evaluation as related to dermatopharmacology and dermatotoxicology.