The main component of reactive oxygen species, free radicals are very reactive molecules with unpaired electrons that harm cells and cause oxidative stress. They have a substantial impact on conditions like cancer, neurodegeneration and cardiovascular disorders. Different characteristics and reactivities are displayed by free radicals, including superoxides, hydroxyl radicals, nitric oxide and peroxyl radicals. Every kind of free radical affects inflammation, oxidative stress and the aetiology of illness in a different way. Deciphering the specific characteristics and effects of different free radicals can inform the development of targeted therapeutic strategies to mitigate oxidative damage and promote cellular health. Reactive oxygen species exhibit dual roles as both deleterious and beneficial molecules, influencing various cellular processes. Their properties and molecular effects modulate signalling pathways, impacting cell growth, differentiation and survival. It activates the key signalling pathways, like MAPK/ERK, PI3K/Akt, NF-κB, Jak-STAT, PKC, P53 and Nrf2/Keap1, influencing cell fate decisions. These pathways orchestrate responses to oxidative stress, regulating inflammation, survival and antioxidant defences, with implications for disease mechanisms and treatment strategies.