A high concentration of oxygen damages cells.
[16] Higher than normal concentrations lead to increased levels of
reactive oxygen species (ROS),
[46] and while not all mechanisms of damage are understood, the process of
lipid peroxidation is known to cause damage to
cell membranes.
[47] ROS form as a natural byproduct of the normal
metabolism of oxygen and have important roles in
cell signaling. However, during times of environmental stress ROS levels can increase dramatically, which can result in significant damage to cell structures. This cumulates into a situation known as
oxidative stress.
[16][48] One example is that oxygen has a propensity to react with certain metals to form the ROS
superoxide, which attacks
double bonds in many
organic molecules, including the
unsaturated fatty acid residues in cells.
[49][50] High concentrations of oxygen are also known to increase the formation of
free radicals which harm
DNA and other structures (see
nitric oxide,
peroxynitrite, and
trioxidane).
[16][51] Normally the body has many defense systems against such injury, such as
glutathione,
catalase, and
superoxide dismutase, but at higher concentrations of free oxygen, these systems are eventually overwhelmed, and the rate of damage to cell membranes exceeds the capacity of the systems which control or repair it.
[52][53][54] Cell damage and cell death then result.
[55]