Minimal erythema dose after multiple UV exposures depends on pre-exposure skin pigmentation
Version of Record online: 6 JUL 2004
Photodermatology, Photoimmunology & Photomedicine
Volume 20, Issue 4, pages 163–169, August 2004
How to Cite
Henriksen, M., Na, R., Ågren, M.S. and Wulf, H.C. (2004), Minimal erythema dose after multiple UV exposures depends on pre-exposure skin pigmentation. Photodermatology, Photoimmunology & Photomedicine, 20: 163–169. doi: 10.1111/j.1600-0781.2004.00104.x
- Issue online: 6 JUL 2004
- Version of Record online: 6 JUL 2004
- Accepted for publication 12 May 2004
Background/purpose: Phototherapy consists of multiple ultraviolet (UV) exposures. Most previous studies have focused on erythema following a single UV exposure in fair-skinned persons. Although it is well known that phototherapy lowers the daily UV-threshold dose for erythema in clinical practice, this is insufficiently documented under controlled experimental conditions. The purpose of this study was to quantify the change in the daily threshold for a dose specific erythema grade after 1–4 consecutive daily UV exposures.
Methods: Forty-nine healthy volunteers (skin type II–V) with varying pigmentation quantified by skin reflectance. Two UV sources were used: a narrowband UVB (Philips TL01) and a Solar Simulator (Solar Light Co.). Just perceptible erythema after 24 h was chosen as the minimal erythema dose (+); besides + and ++ were assessed.
Results: We found a positive and significant exponential relationship between skin pigmentation and UV dose to elicit a specific erythema grade on the back after 1–4 UV exposures. After repetitive UV exposures the UV dose had to be lowered more in dark-skinned persons compared with fair-skinned persons to elicit a certain erythema grade. This applied to both UV sources and all erythema grades.
Conclusion: In the dark-skinned persons the daily UV dose after the 4 days UV exposure should be lowered by 40–50% to avoid burns compared with the single UV exposure. For the most fair-skinned persons essentially no reduction in the daily UV dose was needed. Our results indicate that the pre-exposure pigmentation level can guide the UV dosage in phototherapy.