Thermal contraception

Thermal contraception uses your body’s own heat to put sperm production on pause. It involves no hormones and no surgery, and a simple lab test, the semen analysis, tells you at every stage whether it’s working. The results of the studies are very encouraging, but more data is still needed.

Already familiar with the method? Skip straight to the step-by-step practical guide.

🗺️ Where does the method come from?

The first observations go back to the 1930s. In India, a Swiss doctor, Marthe Voegeli, described daily hot baths that lowered fertility for a while¹. She reported nine cases, in a manuscript that no journal ever published.

In France, clinical research began in the 1980s at Toulouse University Hospital. Dr. Roger Mieusset and his team lifted the testicles of male volunteers using briefs with an opening cut into them. Their 1994 study followed nine couples, and among the six couples who stayed until the end, the team saw no pregnancies over 117 cycles². It’s a proof of concept: the group is too small to measure how effective the method is. In 2012, Roger Mieusset and Jean-Claude Soufir published the practical guide that is still the reference for the protocol⁴.

The method then made its way out of the hospital through activist groups. Sewing workshops let anyone make their own jockstrap, and then came silicone rings, which several collectives make today.

🌶️ Why “thermal”?

Spoiler: the ring doesn’t heat up. Your body does all the work.

First, a quick anatomy lesson.

The testicles make sperm in the scrotum, outside the body, at a temperature 2 to 4°C (roughly 4 to 7°F) lower than the rest of the body⁵. This process, spermatogenesis, takes about 74 days⁵.

When the testicles move up inside the body, into the inguinal canals, they gain one to two degrees Celsius². One review estimates that each extra degree Celsius in the testicle lowers sperm production by about 14%⁵. Day after day, sperm concentration goes down, until it falls below 1 million sperm per milliliter of semen. That’s the threshold andrology societies set for hormonal contraception, and we use the same one for the thermal method⁹.

🪄 So, how do you do it?

You hold your testicles up, at the base of the penis, near the entrance to the inguinal canals: that’s testicular elevation⁴. Before birth, the testicles came down into the scrotum through these same canals.

Several tools can hold the testicles in this position: the silicone ring, the hand-sewn jockstrap, or the briefs designed in Toulouse. Our rings are prototypes without CE marking.

With a ring, you first slide your penis through it, then the skin of your scrotum. Sitting at the base of the penis, the ring keeps the testicles up. It has to stay in place without ever squeezing. Feel gently around your pubic area to check that the testicles are up.

Articles on the subject often talk about “heated briefs.” That’s a misnomer: the Toulouse briefs and the jockstrap lift the testicles, just like the ring, and don’t warm them any more than it does. There are also devices that really do heat, above body temperature, and they belong to a different method. We explain the difference on the heated briefs page.

📆 Do I have to lift my testicles every day?

Yes. The Toulouse guide asks for 15 hours of elevation a day, every day⁴, during waking hours². In practice, you put the ring on when you get up and take it off when you go to bed.

Lifting your testicles every day can feel daunting at first. Once you’re used to it, it becomes as automatic as putting on your socks in the morning.

To start, you build up wearing time in steps over one to two weeks: one hour, then two, four, six, then the whole day. This gradual start comes from the community, and no study has tested it.

What if you take a break? If you stop for more than 24 hours, the effect is no longer guaranteed⁴. In that case, you restart the protocol and use another method of contraception until a new semen analysis, done at least a month after the break, comes back below the threshold.

✅ Does it really work?

No contraceptive method is 100% effective in real life, not even vasectomy. With the thermal method, semen analyses let each person check the effect for themselves: everyone runs a small scientific protocol of their own.

The TESTIS survey asked 970 people who had been using the method for more than six months. Of the 966 counted for the Pearl Index, 6 unplanned pregnancies were reported, which gives an index of 0.53: roughly one pregnancy per 190 years of combined use⁶. The survey only counts people who had used the method for more than six months, so its numbers are optimistic by design⁶.

In clinical trials, the Pearl Index goes up to 2.9, or about one pregnancy per 35 years of use⁸. Those trials used devices other than the silicone ring: no clinical trial has looked at the ring yet, and what we know about it comes from surveys and self-reported follow-up⁷.

Not everyone gets below the threshold. In the CRT-REVERS follow-up, 54 of 66 people reached it, or 81.8%⁷, and the studies don’t say whether the others reach it later. When fertility doesn’t drop enough, we first look at how well the testicles are held up, for example by changing ring size.

With no large trials yet, the European and American andrology societies have recommended since 2024 not using heat as contraception for now, while acknowledging that it has prevented pregnancies⁹. You can read the studies, one by one (in French).

🩺 What about my health?

At 15 hours a day, the Toulouse team saw no major change in testosterone, or in the hormones that control the testicles. Testicle volume drops by less than 20% and returns to normal within a year of stopping³. At 24 hours a day, on the other hand, testosterone drops by about 40%, while staying within the normal range, and testicle volume by about 35%³.

Side effects mostly affect the skin. In TESTIS, 94.8% of respondents report at least one⁶, and depending on the study, skin irritation affects 27 to 53% of people⁸. At first, elevation can also cause discomfort or mild pain. In our experience, this discomfort fades with time, a bit like when you take up a new sport.

The studies also describe a few isolated, more serious cases, including a penile vein thrombosis, a case of priapism, and three cases of testicular induration (0.3%)⁸. If you notice a side effect, take the ring off and ask a healthcare professional for advice: a general practitioner, a urologist, or an andrologist.

And testicular cancer? As far as we know, no study has measured this risk with the thermal method, so we don’t know.

As a precaution, since there are no studies, the guide advises against the method in several cases⁴: a testicle that didn’t descend normally (cryptorchidism, ectopic testis), whether or not it was operated on; an inguinal hernia, operated on or not; testicular cancer; a grade 3 varicocele; and severe obesity.

🧭 Where do I start?

A healthcare professional and a first semen analysis. An appointment with a doctor (general practitioner, urologist, andrologist) lets you rule out contraindications, and if you or your partner see a midwife, they can point you in the right direction too. The guide then asks for a normal semen analysis before you start⁴. Get it before you wear the ring, or your fertility will already have dropped: this first result tells you where you’re starting from, and you’ll compare every later one to it. A low result at the start doesn’t mean you can skip contraception, so talk it over with your doctor before you begin¹⁰. Ask for a repeat prescription for the follow-up semen analyses too. The contraception map helps you find a healthcare professional who knows the method. Most of them are in France.

An information session to find your size. If it’s too small, the ring leaves marks and squeezes. If it’s too big, it slips and lets the testicles drop back down. The only way to find your size is to try rings on: after an information session, we send you a trial kit with twelve sizes¹¹.

Follow-up semen analyses. The Toulouse guide asks for one a month until the sixth month, then one every two months⁴. We suggest at least one every three months, and more often to lower the risk. To compare your results with each other, keep the same number of days of abstinence before each test. Everything about the semen analysis: where to get one, what it costs, how to read your results.

The day you want to stop. You take the ring off, production starts again, and you need another method of contraception from day one⁴. In CRT-REVERS, across all 179 respondents, the median time to a pregnancy after stopping was 5 months. Of the 66 people whose semen analyses were reviewed, 9 were still below normal values more than three months after stopping⁷. If you want a child, plan when you’ll stop and talk it through with a healthcare professional. The guide also recommends not going beyond 4 years of use, the length of time over which reversibility has been observed⁴.

💞 How does it work as a couple?

Consent is the foundation of any romantic and sexual relationship. With the thermal method, the person who makes the contraception work isn’t the one who takes the risk of pregnancy. Contraception is something you choose, check, and decide together, and your partner has every right not to trust testicular contraception.

You have to use another method of contraception, condoms for example, until a semen analysis has shown a concentration below 1 million sperm per milliliter. What counts is the test result, not how long you’ve worn the ring: three months of wearing it isn’t enough without a semen analysis below the threshold.

Before having unprotected sex, a second semen analysis, three weeks after the first, checks that the first wasn’t a one-off result. That’s the criterion of the Toulouse guide, which considers the threshold reached after two semen analyses below one million, three weeks apart⁴.

After that, it’s a choice you make together. The thermal method can absolutely be combined with other contraceptive practices, for extra security. It’s not about replacing other methods of contraception, but about developing an alternative, to use in addition to or alternating with other methods.

To set the level of risk that works for both of you, we suggest four settings:

1. Testing. You decide how often to get semen analyses, and how many matching results you want before having unprotected sex. The more tests you do, the more confident you can be in the method: a first test below one million after three months doesn’t give the same confidence as five or six matching tests over two years.
2. Wearing time. Wearing the ring less than 15 hours a day isn’t recommended. If you do it anyway, more frequent semen analyses will tell you whether fertility stays below the threshold.
3. The fertility level you aim for. The lower the fertility, the more effective the method, and you can aim below one million to give yourselves some margin.
4. Combining methods. With two methods, both would have to fail at the same time for a pregnancy to happen, and the risk drops sharply.

These settings can change along the way, and you can revisit them as soon as one of you no longer feels confident. We go into this in more depth in Managing contraception as a couple (in French).

The thermal method doesn’t protect against any sexually transmitted infection, so it doesn’t replace condoms. And even though testicular methods let you share the contraceptive burden, they don’t erase the mental load for partners. Quite the opposite.

💍 What about Otoko’s rings?

For now, our rings are prototypes: they have neither CE marking nor a marketing authorization from the ANSM, France’s health products regulator. The ring should not be considered a contraceptive ring: it has no active contraceptive ingredient, and neither its contraceptive properties nor its safety have been demonstrated. It can be used as a cockring shaped for testicular elevation, with full awareness of the associated risks.

Our rings are cast in platinum-cure silicone, a type also used for medical devices. Our manufacturing methods are open, and other collectives make their own rings too.

🚪 What’s next?

To get rings, the first step is a pay-what-you-can information session, on your own or as a couple. In English, it’s a video call with Sam, wherever you are; the sessions in Pantin, next to Paris, are in French. We talk about the protocol, semen analyses, contraception as a couple, and your size, and you can ask all your questions. Outside France? After the video session, the trial kit ships to you too. Only the shipping changes, and you’ll see the cost for your address on the start page.

Book an information session

If you’d rather make your own rings, workshops take place in Pantin and with collectives in several cities, all in French: see all the workshops.

Want to go deeper, at your own pace? The step-by-step practical guide.

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