Major skin-relevant contributors to oxidative stress: 1. UV - sun exposure - sunburn - tanning beds 2. Environmental - pollution - cigarette smoke - some chemicals 3. Inflammation - inflammatory skin disease - injury - wound healing - illness 4. Internal metabolism - mitochondria naturally produce ROS - ageing alters oxidative balance 5. Lifestyle/systemic factors - smoking - excessive alcohol - significant chronic stress - poor sleep - some medications/drugs Oxygen isn't bad and exercise isn't inherently oxidative damage. Exercise can transiently increase ROS but regular exercise also up-regulates antioxidant defence systems.

Your eyes tell you what the skin is doing; the history helps you work out why