 A study by Tobi et al., in 2002 has linked ROS with cytotoxicity, apoptosis, mutations, and carcinogenesis.Mild hypoxia (1-5%) sensitized keratinocytes to UVB-induced apoptosis, while protecting melanocytes from environmental stresses.A study by Mark Schotanus, et al., has demonstrated that in addition to potential damage to keratinocytes and melanocytes, exposure to UVB radiation may also produce a loss of potassium ions, which may then cause the activation of apoptotic pathways in lymphocytes and neuronal cells as opposed to keratinocytes and melanocytes.