Oxygen is toxic to sperm and leads to decreased sperm function and death. This is in addition to the detrimental effects of air on sperm as the semen dries when the ejaculate is exposed to the environment.
Effect of Oxygen on Sperm Survival
Sperm is a complex cell that is vulnerable to a number of conditions including exposure to oxygen. According to a 1998 article in an Oxford journal, Human Reproduction, it has been known since 1943 that when sperm is exposed to oxygen, the molecule interferes with several vital sperm functions. Researchers now know oxygen causes generation of free radicals in sperm, and these molecules are extremely damaging to sperm and its survival.
The Effects of Oxygen-Generated Free Radicals
Oxygen reacts with lipids in the sperm and mitochondrial cell membranes to produce oxygen-containing free radicals, also known as reactive oxygen species (ROS). When sperm is exposed to an excess of these species, the results are:
- Damage to and decreased motility of the sperm tail (flagellum)
- Damage to the sperm head and sperm DNA
- Decreased ability of the sperm to fertilize an egg
- Sperm death
ROS generation occurs immediately on exposure to oxygen and the toxic effect on sperm function and survival occurs rapidly.
Exposure of Sperm to Air
When sperm is exposed to air, it can be assumed the oxygen in the air will react with the sperm in a lethal manner and diminish or abolish the chance of fertilizing an egg. However, it is likely that even more lethal is the drying effect of air on semen and therefore the sperm. Semen dries quickly on exposure to air and within seconds to a few minutes, the sperm will be dead depending on how fast the semen dries.
Sperm cannot survive unless it is in semen, fluid in a woman's genital tract such as the fallopian tubes, or in culture medium during preparation for in vitro fertilization (IVF). Even in these fluids, the lifespan of the sperm is limited. For example, in culture medium the sperm is vulnerable to reactive oxygen species, so antioxidants are added to the medium according to an article in Seminars in Endocrinology.
Sperm Is Susceptible
Sperm is especially susceptible outside of the protective environment of semen and with exposure to oxygen or other environmental factors, it will die. It is packaged for the single goal of delivering its DNA to the egg and has no tools or chance to repair itself when exposed to oxygen or other detrimental factors.