We really don't know why cabbage leaves are helpful, but it is
apparently not just because they are cold.
See Journal of Human Lactation 11(3), 1995, pp191-194.
"A Comparison of Chilled and Room Temperature Cabbage Leaves in Treating
Breast Engorgement" by Kathryn Roberts, Maureen Reiter, and Diane
Schuster.
"There was no difference in the post-treatment ratings for the two
treatments; mothers reported significantly less pain with both
treatments."
Catherine Mallon, LLLL
Sherwood Park, Alberta, Canada