Department of Biosciences at Novum, Karolinska Institute, Sweden and Päijät-Häme Central Hospital, Lahti Finland

Correspondence: Prof Kari Hemminki, Karolinska Institute, Novum, Huddinge 141 57. Email: Kari.Hemminki@cnt.ki.se

Received 3 June 2002; Accepted 11 July 2002.

Abstract

^{Sheehan et al (2002)} published a paper on UV-dimers in human skin and their repair with contradictions in their own data. In one experiment they applied two doses, 0.65 and 2 MED, but the apparent dimer levels, measured by a immunohistochemical technique, only increased in skin of type II (Fig 2a). The authors offered as explanation that the level of DNA damage would saturate. The dimer levels reached are at around 1 dimer per 1 million nucleotides, and there has been no evidence for saturation when a quantitative postlabeling technique has been used (^{Bykov et al, 1998}). There is no reason for saturation until most of the thydmidyl-thymidine positions would be occupied in DNA, which, based on literature with other intrastrand cross-linkers, would require dimer levels 1: 100 (^{Försti et al, 1989}), or 10,000 times higher levels of dimer than that obtained by an irradiation at a MED dose.