Testicles hang outside the body for a reason. Optimal sperm production requires temperatures that are a few degrees below body temperature. By dangling free, your balls get natural air conditioning that keeps them just the right temperature to build baby-makers. This is great if you are interested in having children right now, but what if you are more concerned about NOT having children?

As it turns out, exposure to heat can actually be used to reduce sperm count. Sperm are much more sensitive to heat than the rest of the body. Prolonged exposure to heat sources such as hot tubs is a well-known cause of reduced sperm count. Repeated and consistent exposure to heat can knock down sperm count so low that it can render a man temporarily infertile.Can a hot tub be used as contraception? How would men know if they could rely on it? Well, think about it. How you know if you spent enough time heating your balls? How do you check if it worked? What happens if you skip a day or two? Does it work for all men, or just some? I’ll have some answers for you later, but first I’ll try to explain how humanity found out that heat may be used to prevent unplanned fatherhood.

A History of the heat method

It has long been observed that men who work in professions that expose them to heat in the nether regions: bakers, cooks, steamworkers; have had a hard time fathering children. Interestingly, men in these professions were observed to start having children after retiring or finding a new job. Based on these observations, Dr. Martha Vogeli ran a long set of experiments starting in the 1940’s in India. After trying all possible combinations, Dr. Vogeli found a consistent method for inducing temporary infertility in men by a series of hot baths. In short, men who sat in hot water for 45 minutes a day for 3 weeks were protected for at least 6 months.

To achieve 6 months of birth control, the water had to be hotter than the typical hot tub (100-104⁰F). According to Dr. Vogeli, it had to be 116⁰F, similar to a 30 minute old cup of coffee. Lower the temperature to a more comfortable 110F (like a hot shower), and the men were good for at least 4 months.

Dr. Vogeli became a lifelong advocate for the method, and apparently made this a locally popular method of birth control around her test site in India. However, the lack of easily accessible technology to maintain the required temperature, and the inconvenience of sitting in hot water for 45 minutes a day made this method a tough sell. As a woman of the 1940s and 50s, Martha Vogeli also found it difficult to get skeptical men to take her research seriously. The approval of the first female birth control pill in 1957 probably contributed to the lack of popular uptake. Dr. Vogeli’s research was largely forgotten until researchers revisited the link between heat exposure and unexplained male infertility decades later.

A second method for getting the required heat is to get it from the body. This method saw some scientific research in the 1980s and 90s. Remember that sperm production requires temperatures LESS than your core body temperature. Researchers found that underwear that pushed the balls up into the body (aka suspensories) were effective in significantly reducing sperm count. Sperm counts could be suppressed as low as 3 million per milliliter (for comparison, the threshold for male sub-fertility is 15 million per milliliter), and most of these cells could no longer swim. When applied consistently, the method proved to be effective at preventing pregnancy. The catch was that the special underwear had to be worn during all waking hours: about 16 hours a day to be effective.

Wearing funky underwear never caught on as a birth control technique. Men are famously loyal to their favorite style of undies, not to mention suspensories sound uncomfortable.

Why sperm are sensitive to heat

For unknown reasons, developing sperm are much more sensitive to heat than all of the rest of the cells in your body. Temperatures above about 95⁰F activate a protein called Heat Shock Factor in developing sperm. If activated for a sufficient amount of time, Heat Shock Factor will cause the developing sperm to die before they are finished. In comparison, other cells require sustained temperatures in excess of 105⁰F for activation of Heat Shock Factor. This difference in temperature sensitivity is what allows heat exposure to reduce sperm count while leaving the rest of the body unharmed.

Sperm take about 70 days to fully develop within the testicles. Any interruptions during this development process can reduce sperm count. However, sperm cells that are nearly complete appear to be more temperature resistant than immature cells. For this reason, it takes at least 3 weeks for heat exposure to have an effect on semen quality as the mature cells are cleared out. This is also the reason why a sustained period of heat can have a contraceptive effect for months after exposure. If most developing sperm cells are disabled by heat, it takes some time for the sperm cells to repopulate.

Is it safe to regularly heat your testicles?

Most methods of birth control come with risks and side effects. Applying heat does not involve introducing chemicals into your body or surgery. Preliminary evidence suggests that the various heat methods are safe. All of the men enrolled in Dr. Vogeli’s studies and in the suspensory studies were able to father children later, and none of the children were born with abnormalities. None of the men developed problems with libido (sex drive), and seemed to remain in good health. This suggests that testosterone levels remained normal. The amount of time required to fully recover fertility was between 6 – 18 months, depending on how long the method was employed so coming off of heat-based birth control would take more forward thinking than for some alternatives. A subset of men have been exposed to heat as part of their profession for many years, and there has been no evidence of lasting effects.

That said, there have not been large scale studies to support the safety of the heat method. It is possible that a small number of men would develop problems after continuous use. In one instance, a man who had used the suspensory technique for 8 consecutive years on his own initiative did not fully recover his sperm count for 2 years after discontinuing (although he had a residual count of about 20 million per milliliter). Although evidence suggests that testosterone levels remain normal, long term effects have not received sufficient study. Finally, there is the obvious risk of applying water that is a bit TOO hot to your privates and getting a burn where you don’t want one.

The bottom line: The heat method appears to be safe relative to other methods of birth control, but we need larger studies to say for sure. In the meantime, if you use this method it is at your own risk.

Can heat be used reliably as a form of birth control?

The preliminary data is encouraging. Dr. Vogel and the suspensory researchers both reported 100% contraceptive effectiveness when their methods were applied consistently. However, the number of men who participated in these studies numbers in the dozens in total, so we do not know if it is equally effective for all men. We know that condoms are 98% effective when used as directed, but at this moment cannot put a similar number to the heat method.

That said, the biology behind these techniques seems to be solid. Unlike female fertility, it is possible to check whether a man is fertile by doing a semen analysis. A sperm count below 1 million per milliliter was used as threshold for effective male contraception in a recent study on a potential birth control pill for men. A few adventuresome men have employed a heat method at home, bought a microscope, and reported their results to the world over time. It appears that these men were able to reduce their sperm counts to near zero by dedicated adherence to their respective methods. The recent proliferation of home sperm testing kits may make applying these techniques, and seeing if they worked, more feasible.

Considerations for implementing DIY heat based birth control

To re-iterate, there have not been large scale studies to prove that the heat methods are safe for long term use. Nonetheless, there are few dedicated men who have reported their experiences with heat methods online. These enterprising do-it-yourselfers have reported a variety of techniques ranging from programmable warmers (such as a programmable coffee warmer) for Dr. Vogel’s hot water method to custom undies for the testicle suspension method. A means of testing sperm count at home is also essential equipment for these enthusiasts because it would otherwise not be obvious if the technique was actually working. The tools and information are obviously out there, but it is an experimental technique that you try at your own risk.

There is a great need for more research to see if a heat method could be workable contraception for more men. Not every woman can tolerate extended hormonal birth control, and the side effects are severely underrated. For instance, there is at least one report of a man controlling his fertility for the sake of his hormonal pill-intolerant girlfriend through a rigorous monthly ritual of hot baths. In addition, not every man who wants to control his fertility is ready to take the surgical option and get a vasectomy. Perhaps one day researchers will put in the resources to prove the method to be safe and reliable on a larger group of men.