The air we inhale contains 21% oxygen that instantly combines with haemoglobin(in RBC) itself that reaches various cell that helps to produce energy. However some inhaled oxygen turned into free radicals that is highly unstable and can be harmful. Our body produces antioxidants that nutralise free radicals .
But if we consume pure oxygen for long time then number of free radicals increases and it become difficult for antioxidants to nutralise them.Then free radicals combines with various protien of RBC and change their structure. As a result our immune system doesn't recognize RBC and begins to kill them. Besides this free radicals can lead damage to DNA which can lead to cancer.
