**6. Conclusion**

This chapter briefly summarized types of antioxidants, and their mode of action. The harmful products formed during normal cellular functions are oxygen radical derivatives that are the most important free radical in the biological system. For normal physiological functioning, it is important to maintain a tolerated antioxidant status by increasing intake of natural antioxidants. Studies have shown that different types of antioxidants, including natural and synthetic antioxidants, can help in disease prevention. The antioxidant compounds may directly react with the reactive radicals to destroy them via accepting or donating electron(s) to directly remove the unpaired status of the radical. Moreover, they may indirectly reduce the production of free radicals by inhibiting the efficacy or expressions of free radical creating enzymes or by stimulating the activities and expressions of other antioxidant enzymes. Thus, it is essential to know the antioxidant mechanisms of action with the free radicals.

*Antioxidants*
