Peer-reviewed research on testicular temperature, thermal exposure, scrotal cooling, and their observed relationship with male reproductive health.
This study looked at how occupational heat exposure and fertility-related stress might affect semen quality. It compared 485 men, split into groups with normal and low semen quality based on…
This study set out to see if sperm quality changes with the seasons in Denmark and Florida, and whether outdoor temperatures play a role. It looked at semen samples from…
This study measured how outdoor temperature tracks with semen quality, using records from 5,114 men attending a reproductive medicine centre in Wenzhou, on China's east coast. The measure it used…
This review looked at whether the underwear a man wears, tight versus loose, actually affects his fertility. The testicles work best a little cooler than the rest of the body,…
Researchers followed 1,220 men at a Utah fertility clinic and matched the outdoor heat and humidity each man lived through while his sperm were forming against a molecular measure of…
This review gathers recent evidence on what damages male fertility and how much of it can be undone. Smoking raises sperm DNA fragmentation (breaks in the genetic material inside sperm)…
This study asked which workplace exposures matter most for men's reproductive health. It took 80 men working in an automobile parts plant, measured their exposure to magnetic fields, electric fields,…
This study looked at how lifestyle and hormones affect semen quality and sperm DNA health in men. It examined 278 Indian men aged 21 to 50, measuring sperm count, movement,…
This study looked at how the smallest blood vessels in the skin respond to a hot bath, and whether that differs by ethnicity. Thirty-one healthy young men (10 White-European, 10…
This study measured what happens to scrotal temperature during a run. Eleven trained long-distance runners ran on a treadmill for 60 minutes at 60% of their maximum aerobic capacity, in…
This study tested whether making training harder by adding heat, thin air, or both improves short-burst cycling power. Eighty untrained young men were split into five groups of 16: no…
This study followed 2,575 Finnish men aged 42 to 61 for a median of 27.8 years and asked whether sauna habits change how dangerous high blood pressure is. Over that…
This is a narrative review, which means the authors gathered and discussed existing work rather than running a study of their own. It asks whether the damage COVID-19 does to…
This meta-analysis set out to work out how high ambient temperature affects sperm quality. It pooled nine studies covering 356 men in Iran, Italy, Thailand, China and Egypt, comparing men…
This study looked at whether adding sauna sessions after exercise affects gut bacteria, intestinal barrier function, and inflammation in young men. Fifteen untrained men were split into two groups: one…
This study asked whether a man's heat exposures affect how quickly his partner conceives, which is a harder and more useful question than whether they affect a semen sample. It…
This meta-analysis set out to see whether repeatedly getting the body used to heat raises HSP70 (heat shock protein 70, a protein cells make to protect themselves from heat damage)…
This study set out to find which stage of sperm production is most sensitive to mild heat. Five healthy volunteers wore a specially designed underwear that held the testicles up…
This study looked at whether plunging into cold water after weight training costs a man muscle growth or strength. Sixteen men trained three times a week for seven weeks, half…
This study asked what a mild, sustained rise in testicular temperature does to the chromosomes inside sperm. Five fertile volunteers wore specially designed underwear that held the testicles up against…
This review pulled together what is known about how everyday life affects a man's fertility, covering age, psychological stress, nutrition, physical activity, caffeine, scrotal temperature, hot water and mobile phone…
This study set out to see if regular sauna use is linked to lower inflammation and oxidative stress over time. It tracked 2269 middle-aged men for 11 years, measuring markers…
This study set out to review the evidence on whether sauna could help people with heart failure. It pooled data from nine studies, seven of which were included in a…
This systematic review set out to test the health claims made for regular dry sauna use, because the claims are common and the evidence behind them had never been gathered…
This is a history of forty years of French research into male contraception (hormonal, chemical and thermal) summarising clinical trials involving thousands of men and couples. Those trials established that…
This study set out to see whether regular sauna use might lower the risk of developing high blood pressure. It tracked 1,621 middle-aged Finnish men without hypertension at the start,…
This study set out to see if regular sauna use might lower the risk of respiratory diseases like chronic obstructive pulmonary disease (COPD), asthma, and pneumonia. It followed 1,935 middle-aged…
This experiment followed what whole-body heat does to sperm as they are made, in laboratory mice. Adult males were held at 37 to 38 degrees Celsius (98.6 to 100.4 degrees…
This study set out to see what repeated heat does to sperm. Twenty men with normal semen results were randomly split into two groups, and both had their testicles warmed…
This study set out to see what sustained scrotal heating does to semen and to the sperm's genetic material in fertile men. Nineteen healthy volunteers wore a warming belt at…
This study looked at what sustained scrotal heating does to semen and to the sperm's genetic material in already fertile men. Twenty-five healthy volunteers wore a warming belt at 40…
This paper reports two separate experiments on whether cold water after strength training blunts the adaptation to it. In the first, 21 physically active men trained for 12 weeks, twice…
This study set out to see whether how often a man used a sauna tracked with his chance of dying, of heart disease or of anything at all. It followed…
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…
This study set out to see how regular sauna use affects sperm health in men whose sperm counts were normal to begin with. Ten men used a Finnish sauna twice…
This review set out to see whether sweating clears toxic metals from the body. It pooled 24 studies that measured arsenic, cadmium, lead and mercury in sweat, compared those levels…
This study set out to see whether heat on its own triggers some of the same responses in the body as exercise. Twenty-five healthy young adults, 13 men and 12…
This experiment asked whether heat reaches sperm that have already been made, rather than only the ones still forming. Fourteen C57BL/6 mice (a laboratory strain bred so that individuals within…
It has been suggested that cycling warms the testicles as a ride goes on, and that this in turn harms semen quality. This study tested the first half of that…
This study looked at whether stopping hot tubs, hot baths and whirlpools improves semen quality in infertile men. Eleven men with a regular wet heat habit were assessed before and…
This experiment asked whether heat makes sperm worse at their actual job, or simply leaves fewer of them. Male mice were held at 36 degrees Celsius (96.8 degrees Fahrenheit) for…
This study set out to measure how much using a laptop on your lap raises scrotal temperature, a known risk factor for male infertility. Researchers measured scrotal temperature in 29…
This study looked at what a fever does to semen quality in healthy men. Twenty-seven men with a median age of 24.4 years gave a semen sample every month and…
This study asked why men differ so much in how warm their testicles run. Scrotal skin temperature was logged every five minutes for 24 hours in 48 men, made up…
This study set out to find which parts of an ordinary day actually move scrotal temperature. A thermistor (a small temperature sensor) was clipped to the underwear of 101 men…
This study asked whether the ordinary, everyday variation in scrotal temperature is enough to matter for sperm. Sixty men from a group of couples planning their first pregnancy wore a…
This lecture is the field's own summary of why the testicles sit outside the body and what happens when they get warm. It sets out the evidence that the testes…