The effect of pre-phototest sun exposure on minimal erythema dose and minimal melanogenic dose among skin phototypes III, IV and V

BACKGROUND: Ethnicity, skin phototype and colour influenced minimal erythema dose (MED). Sun exposure has been postulated to increase MED. We determined immediate pigment darkening dose to UVA (IPDDA), MED and minimal melanogenic dose (MMD) for UVB and UVA, and investigated factors affecting these doses.

METHODS: Skin phototype was determined using Fitzpatrick phototype quiz, DSMII ColorMeter measured skin colours, sun exposure quantified using an index (SEI) and phototest performed with MEDlight-Multitester.

RESULTS: A total of 167 healthy volunteers participated. There were 110 (66%) females and 56 (34%) males; 124 (74.7%) were Malay, 27 (16.3%) Chinese and 14 (8.4%) Indians. One hundred and nine (65.7%) skin phototype IV, 30 (18.1%) phototype III and 27 (16.3%) phototype V. IPDDA ranges from 6 ± 1.5-5.7 ± 1.4 J/cm2 . MED-UVB were 96.9 ± 17.6, 124 ± 29.3 and 118.6 ± 27.4 mJ/cm2 for phototype III, IV and V, respectively. All MED-UVA were outside the tested dose range of 3.6-11 J/cm2 . MMD-UVB were 106 ± 18.2, 134 ± 25.6 and 136 ± 31.1 mJ/cm2 while MMD-UVA were 4.1 ± 4.1, 4.9 ± 3.8 and 5.7 ± 3.7 J/cm2 respectively for phototypes III, IV and V. MED-UVB, MMD-UVB and MMD-UVA did not depend on skin phototype. Facultative skin whiteness (L*), erythema (E) and melanin content (M) correlated significantly with MED-UVB while constitutive skin colours were significant for L*, yellowness (b*), E and M. Sun exposure did not significantly correlate with MED-UVB and MMDs, however, an inverse relationship with MED-UVB was demonstrated.

CONCLUSION: Minimal erythema doses in our cohort were slightly different from other regional countries. Constitutive and facultative skin whiteness, erythema and melanin content correlated with MED. There was no association between skin phototype and sun exposure with MED or MMD.