It helps to boost the immune system and improve blood circulation. Rosemary is rich in antioxidants, which play an important role in neutralizing harmful particles called free radicals. Rosemary contains an ingredient called carnosic acid that is able to fight off free radical damage in the brain. It enhances memory and concentration - blood levels of a rosemary oil component correlate with improved cognitive performance. Research shows rosemary may significantly help prevent brain aging. Rosemary has differential anti-proliferative effects on human leukemia and breast carcinoma cells.