The story
Unknown, but probably via Scandinavian forms such as Swedish mässlingen (“pustules, measles”), Danish mæslinger (“measles”), Icelandic mislingar (“measles”), etc. combining the Germanic roots related to blood blisters with the suffix -ing. In reference to delamination, possibly a separate derivation from measle + -ing under influence from the dialectal name for the disease.
Etymology from Wiktionary, CC BY-SA 4.0.