i found this little blurb on the web at
it provides a partial answer to your question.
Lactation consultants frequently suggest cabbage leaves to reduce swelling in moderate to severe engorgement. References to cabbage compresses for swelling and engorgement date back to the early 1800's. Cabbage compresses have been used to reduce the swelling in sprains and broken bones. Research data is sparse but published studies and anecdotal reports seem to support its value in reducing breast engorgement.
The common green cabbage (Brassica capitata) is used for engorgement therapy. Cabbage is known to contain sinigrin (allylisothiocyanate) rapine, mustard oil, magnesium, oxylate and sulphur heterosides. Herbalists believe that cabbage has both antibiotic and anti irritant properties. It is theorized that this natural mixture of ingredients helps decrease tissue congestion by dilating (opening) local capillaries (small blood vessels) improving the blood flow in the area.
Cabbage compresses should be used with other engorgement treatment routines