Is the Thermal Method Among the Natural Remedies to Prevent Pregnancy?
Key Points
- When it comes to pregnancy prevention, women have a suite of options to choose from. Men, however, get to choose between condoms and vasectomies.
- In the ongoing quest for male-centered contraceptives, scientists have developed various concepts, but few have made it past the first stages of clinical trials.
- Research suggests the thermal technique—one of a slate of natural remedies to prevent pregnancy—may decrease sperm count and motility by raising the testes' temperature.
From mango seed to the rhythm method, people have for centuries attempted to find natural remedies to prevent pregnancy. Unfortunately, these tend to be unreliable at best and—like the pill, IUDs and most other modern methods—they typically require women to shoulder the responsibility and consequences.
Enter the thermal method, which purports to give men an equal opportunity without the need for condoms, surgical intervention or impeccable timing.
What is the thermal method of contraception?
"Heat-based contraception relies on the fact that the testicles are sensitive to temperature changes," said Jagan Kansal, M.D., a Chicago-based urologist and the founder of Down There Urology. "That's why the testes are located outside the body. An average temperature of 93.2 to 95 Fahrenheit [34 to 35 degrees Celsius] is ideal for sperm production.
"Prolonged heat exposure can, over time, diminish sperm motility and production and potentially render a person infertile—at least temporarily."
Men have a few ways to practice the "thermal method," most of which fall into two categories, according to John Reynolds-Wright, M.B.Ch.B., Ph.D., a clinical lecturer at the University of Edinburgh's MRT Centre for Reproductive Health in the United Kingdom.
"One camp, the 'French approach,' involves separating the testes from the scrotum, tucking the former into the inguinal canals and holding them there for several hours at a time," he said. "Another option, mostly popular in the United States, involves taking multiple scalding baths a day."
The first technique raises the temperature of the testes by 1.8 to 3.6 degrees Fahrenheit [1 to 2 degrees Celsius], just enough to inhibit spermatogenesis, the sperm production and maturation cycle.
It initially made headlines with the invention of the "Toulouse Ball-Lifter," a pair of specialized underwear created by researchers at Toulouse University Hospital in France. The same team also developed a prototype of a rubber contraceptive ring held in place by straps.
A word on male contraceptive rings
Otoko Contraception and Thoreme used the same principles to develop rings purported to achieve the same ends with sleeker, subtler designs (and with less amusing names). These are made of silicone and stay in place independently.
The rings and the underwear must be individually fitted, worn for a minimum of 15 hours a day and washed regularly. They take up to three months to reach full effectiveness.
Samuel Flambard, the founder of Otoko Contraception, has used the thermal contraception method since 2021. After finding personal success with his hand-crafted ring, he began offering workshops to teach others how to make their own.
According to Flambard, the rings are easy and cheap to produce and comfortable enough that many users forget they're wearing them after one to two weeks, but that will vary from person to person.
It should be noted that the silicone contraceptive rings were suspended by the French National Agency for Medicines and Health Products Safety in mid-December 2021. They did not have a CE (Conformite Europeenne) marking to signify that they met European Union health, safety and environmental requirements. The French agency wants clinical trial evidence before certifying the rings.
The thermal contraceptive rings are still available for purchase but now as a "work of art."
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- How to Choose the Right Condom for You (and Your Partner): Wrapping it up remains the only way to prevent most STIs. Luckily, there are lots of options—from lambskin and latex to cola-flavored and glow-in-the-dark.
Does heat-based contraception work?
Proponents of the thermal method say research indicates it's 99.5 percent effective with correct use, comparable to the oral contraceptive pill or IUD. That's according to research from the late 1980s and early 1990s cited in a 2017 analysis of the history of thermal contraception. The study cited in the analysis, however, was very small, with only nine couples involved.
No large-scale studies have been carried out.
Since the 1994 Mieusset thermal contraceptive study, other researchers have taken an interest in the method:
- A 2021 study on mice appeared to suggest the method is effective–at least in rodents.
- A 2023 survey reported six unplanned pregnancies among 964 participants who had used the thermal method for at least six months, Flambard said. No pregnancies occurred after the contraceptive threshold—a sperm count below 1 million/mL—was reached.
As with any form of birth control, proper usage is crucial.
The longer someone goes without wearing the underwear or device, the more likely it is that some sperm will survive the first stages of maturation, Flambard said, so users should avoid keeping it off for more than 10 consecutive hours.
After 24 hours without wear, the method would be ineffective. At that point, the user would need to start the protocol over again while using backup contraceptives to prevent pregnancy in the meantime.
Regularly testing sperm count is also vital, according to Flambard. He advises taking a fertility test before starting the method, once more after three months, and then every one to two months thereafter.
More rigorous research is needed, according to Reynolds-Wright.
"Biologically, it makes sense that we know that if the temperature goes up, the sperm count will go down," Reynolds-Wright said. "But in terms of those methods, there are no robust studies that demonstrate how effective they are, how reversible they are, or what other safety considerations there might be."
For his part, Kansal said he "totally" recommends against the technique since there's no sufficient evidence that it works but reason to believe it could do more harm than good.
Why aren't there more male contraceptive options?
"Historically, women have borne the burden of pregnancy," Reynolds-Wright said. "So contraceptive methods that impede a person's ability to become pregnant have always taken priority over those that prevent folks from impregnating others. In terms of the latter, there aren't that many options aside from vasectomies, condoms and the withdrawal method."
Research suggests around 50 percent of pregnancies in the U.S. are unintended, according to data shared by the Office of Disease Prevention and Health Promotion (OASH). Similar numbers are estimated in the United Kingdom, Public Health England suggested.
That demonstrates an ongoing need for new and different contraceptive methods that meet needs unfulfilled by the existing suite of options.
"Reversible, effective male-centered options would enhance reproductive autonomy for all people," Reynolds-Wright said. "Current male methods are either irreversible or not highly effective. Condoms are good at preventing transmission of sexually transmitted infections [STIs] but, with typical use, fail 18 out of 100 times in preventing pregnancy. Vasectomies fail less than one in 2,000 times but are permanent."
Scientists have worked to develop methods analogous to female contraceptives since the 1950s and early 1960s, he said, but have faced several technological challenges in bringing them to market.
"There are biological challenges in that female contraceptives need to prevent ovulation, which happens once per month, whereas a male contraceptive has to prevent sperm production, which happens millions of times a day," he said.
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Also, studies on male contraceptives can be more challenging to devise because they require partners' participation.
"That is a technically more challenging study to do. It's more complicated. It's more expensive," Reynolds-Wright said. "So those end up not being attractive studies to perform for pharmaceutical companies."
Plus, multiple drug trials have been stopped in the early stages because the negative side effects were deemed too burdensome for men, even though the outcome would be perfectly acceptable for women.
Despite the overwhelming hurdles, scientists have not stopped working on a male birth control pill or other reliable method.
Reynolds-Wright is involved in developing a male contraceptive gel that's now in phase two clinical testing, having made it further than any of its predecessors. The topical gel essentially works by "turning off" the part of the brain that tells the testes to produce sperm, according to the Centre for Reproductive Health at the University of Edinburgh.
"If it passes phase two, it will need to complete one or two phase three studies to be eligible for FDA approval," Reynolds-Wright said, adding that the process may take another five to 10 years before the product will be available to consumers.
There's also been headway in the formulation of a male contraceptive pill. Earlier this year, a team at Weill Cornell published a paper documenting the preliminary success of a drug that temporarily stuns sperm. In the lab, the prototype prevented male mice from impregnating females for up to two hours.
"The current lack of options isn't indicative of a lack of interest," Reynolds-Wright said.
To the contrary, his and others' research suggests many cis men have been willing to share contraceptive responsibilities.
"We found that studies going back to the 1970s demonstrated a proportion of men who would be interested in and willing to use a male method, and their female partners were interested and willing to rely on that method, too," Reynolds-Wright said.
"That interest has increased in the past several years as perceptions around sex, reproductive health and gender roles have changed," Kansal said. "Within the past decade or so, the idea of the male being an equal part to fertility has become more widely accepted."
How long does it take for sperm to regenerate?
Semen—or seminal fluid—carries and protects sperm, helping it reach and fertilize an egg. In healthy men, each 0.034 fluid ounce [1 milliliter] of semen typically contains 15 million to 300 million sperm.
It is possible to ejaculate semen without sperm. This is a condition called azoospermia, which is usually a result of issues such as injuries, infections, blockages or hormonal imbalances affecting the testicles.
The thermal technique—like the male contraceptive gel or pill—doesn't cause azoospermia. It may, however, reduce the sperm count to below 1 million spermatozoa per milliliter of semen, which is thought to be low enough to prevent pregnancy.
The testicles produce several million sperm per day, or approximately 1,500 per second. By some estimates, the body can make up to 8 billion swimmers within one spermatogenesis cycle, which takes about 74 days.
Sperm count and health vary from one man to another, but for most, about 50 percent of sperm cells are viable.
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What should you know about heat-based contraception?
Unlike hormonal contraceptive pills, patches, injections and IUDs, the thermal technique doesn't produce side effects such as nausea, weight gain, fatigue, bloating, headaches, irritability, increased blood pressure, or an elevated risk of mood changes and blood clots.
That's not to say there are no downsides.
"Obviously, exposing testicles to red-hot temperatures could damage them and surrounding tissues," Kansal said. "But even the so-called French technique may have adverse effects. For one, although the thermal method's effects are considered reversible, it's unclear if long-term use could permanently impact the testes' ability to produce healthy sperm."
Consider, too, that the testes are located outside of the body for a reason.
"People with undescended testicles which are permanently trapped inside the body from birth are at risk of precancerous or cancerous abnormalities in the affected testicle if it is left inside the body for too long," Reynolds-Wright said. "It's unlikely that the thermal method would contribute to major risks like these, but there are no reliable studies to confirm it wouldn't."
Moreover, there's a chance the thermal method could impede testosterone production.
Low testosterone or low-T could have multiple adverse effects, including erectile dysfunction, fatigue, low libido, loss of lean muscle mass, excess fat accumulation and symptoms of depression, according to the Urology Care Foundation.
Plus, the thermal technique—like all other contraceptive methods besides condoms—doesn't protect against STIs.
The bottom line
Some research suggests the thermal technique has potential as a novel form of low-risk birth control. However, until more research can establish its safety and efficacy, Kansal and Reynolds-Wright suggest relying on other forms of contraception.
"There are lots of contraception options available to couples and there are lots of positives that come from using female methods of contraception, such as bleeding control, help with skin changes, help with mood changes," Reynolds-Wright said. "Also, female methods of contraception actually have clinical trial evidence to support their safety and effectiveness."
