Table 3.

Endogenous and exogenous sources that generate FRs [48].

Endogenous Sources	Exogenous Sources
Inflammation	Exposure to contaminants
Ischemia	Exposure to heavy metals (Hg, Cd, Pb, Fe, and As)
Infection	Chemical solvents
Cancer	Food cooking (smoked meat and used oil)
Activation of immune cells	Medications (cyclosporine, tacrolimus, bleomycin, and gentamicin)
Excessive exercise	Cigarette smoke
Mental stress	Alcohol
Aging	Radiation

Hg: mercury; Cd: cadmium; Pb: lead; Fe: iron; As: arsenic.