Board Thread:Questions and Answers/@comment-26021614-20150408210349/@comment-26292657-20150408215359

Sickness just affects the REC stat, which will reduce healing. Not many bosses have self healing, and a lot that do are immune to it. So its a pretty useless stat against most enemys. Curse stops the enemy from using BB for how ever long its applied, usually more useful than sickness. Again some bosses are immune, so it doesnt always work.