Causes, effects and molecular mechanisms of testicular heat stress.

Plain-language summary

This review gathers what is known about why heat harms sperm production, and how. It sets out the things that raise testicular temperature, from the surroundings a man is in to conditions inside his own body, and then follows the damage down to the level of individual cells. The routes it describes are damage to the DNA inside developing sperm cells, cells switching on their own death program, and cells digesting their own contents when stressed, and it holds that these end in the death of developing sperm cells. Its argument is that sperm production works properly only slightly below core body temperature, so anything that defeats the body's cooling of the testicles has a route to harming sperm. It is a narrative review, so it gathers and interprets rather than pooling results, and it reports no numbers of its own.

Key findings

• Sperm production runs properly only at temperatures a little below the body's core.
• Raised testicular temperature harms both sperm production and the sperm that result.
• The damage runs through DNA damage in developing sperm cells, cells switching on their own death program, and cells digesting their own contents.
• Those routes end in the death of developing sperm cells.
• Both the surroundings a man is in and conditions inside his own body can raise testicular temperature.