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Heat Methods of Male Contraception

The deleterious effect of heat on male fertility has been known since ancient times and is mentioned in Hippocratic writings from the fifth century B.C. (Hippocrates & Adams, 1939 p. 312). Much as aspirin was "discovered" in the 1800s from a bark that Native Americans had long been accustomed to chewing to relieve pain, heat methods have been "discovered" in the past century as a method of male contraception.

These methods derive their effectiveness from the simple fact that the testes must be several degrees cooler than normal body temperature in order to maintain proper spermatogenesis (Fukui, 1923; Moore & Oslund, 1923; Rock & Robinson, 1965; Watanabe, 1959). It is still a mystery why this is so, but one biological advantage has been hypothesized. Since men with high fevers are infertile until they are well again (Kandeel & Swerdloff, 1988), newborns will then be more likely to have healthy fathers, thus increasing infant survival rate.

The body provides cooling by enclosing the testes in the scrotum, which performs a twofold function: it keeps the testes outside the body wall; and it creates a heat exchange between incoming and outgoing blood vessels, much like the one in the coils of a refrigerator (Kandeel & Swerdloff, 1988). When this twofold function is impeded, fertility may be impaired.

Heat’s action on fertility is not completely understood, but at least part of the effect seems to be due to a heat shock factor (HSF) that initiates cell death in sperm above about 95 degrees Fahrenheit (35˚ Celsius), whereas in the rest of the body temperatures of about 108˚ Fahrenheit (42˚ C) are required to disable cells (Sarge, 1995; Sarge, Bray, & Goodson, 1995; Sarge & Cullen, 1997). Contrary to popular belief, men’s briefs do not raise temperatures above that threshold and thus are not a serious threat to fertility (Munkelwitz & Gilbert, 1998). For contraception, a more systematic approach is required, such as one of the following.

Simple Wet Heat

Simple wet heat in the form of hot water, which is inexpensive and available to everyone, was the first systematic contraceptive heat method discovered by the scientific community. In 1946 Dr. M. Voegeli , after more than ten years of experimentation with nine male volunteers, reported on this method. Although time-consuming, the method was perfectly effective and resulted in normal offspring after cessation (Corea, 1985 ch. 9).

Voegeli's program for temporary sterilization is as follows: "A man sits in a [shallow or testes-only] bath of 116 degrees Fahrenheit for forty-five minutes daily for three weeks. Six months of sterility results, after which normal fertility returns. For longer sterility, the treatment is repeated" (Corea, 1985 p. 179). Water at 116˚ Fahrenheit (46.7˚ Celsius) was found to reliably produce at least six months of sterility (Voegeli, 1956). Water at lower temperatures produced shorter periods of infertility; for example, water at 110˚ produced at least four months of infertility.

Voegeli, a Swiss doctor practicing in India, taught the method to Indian men, as well as to seven Western patients (two Englishmen, two Americans, two Scots, and one Austrian), between 1930 and 1950. The doctor saw no side effects and said the use of the method spread widely in that area of India during times of famine, with several hundred men using it (Voegeli, 1954). Children born later were normal, and because Dr. Voegeli practiced in one place for several decades, she was able to confirm that they developed normally as well.

Many men’s first reaction to hearing about the wet heat method is to wonder whether 116˚ water would be painful. They do not know exactly how hot 116˚ is but imagine that it could cause a burn.

For comparison, water heaters are often set at 140-160˚ (60-71˚ C). These are painful temperatures that make people jump and can cause a burn in one to six seconds (Bynum, Petri, & Myers, 1998). Public health authorities recommend setting water heaters at 125˚ in households with children. Temperatures below 120˚ are not dangerous for adults.

The adult pain threshold is often quoted as 118˚ (Long et al., 2001). Below 118˚, comfort depends on how much of the body is exposed, and each degree makes a big difference. Most people enjoy full-body baths and hot tubs at 100-103˚ (37.8˚ C to 39.4˚ C) and cannot tolerate 105˚ for long (Long et al., 2001); however, a hot shower is 108-110˚ Fahrenheit (up to 43.3˚ C) (Shouler & Griggs, 2003). Yet a bowl of water at that same temperature, 108-110˚, does not feel particularly hot, even when a delicate body part such as the testes is immersed. Although a bowl of water at 116˚ does feel decidedly hot, it is actually fairly pleasant. The man’s body quickly absorbs the heat away from the skin, and the body part is small enough that the whole body is not being overheated.

Heat tolerance and safety are temperature-dependent as follows:

Fahrenheit Celsius Typical usage Safety/Sensation on skin
commercial water heater temp. burns in 1 to 6 seconds; very painful
top recommended home temp. burns child in 2 minutes; painful
recommended home faucet temp. uncomfortable; can burn in 10 minutes
- pain threshold for adults
testes-only bath for contraception very hot but not painful
hot shower very warm but not hot
maximum tolerable bath temp. warm
comfortable bath or hot-tub temp. warm


Some of the men in Dr. Voegeli ’s studies reportedly supported temperatures up to 125˚. Unless men of the time had higher pain thresholds than modern men, it seems likely that the temperature may have been dipping a degree or two periodically, explaining their ability to tolerate temperatures reported as being 120˚ or above.

If the temperature was dipping periodically in Dr. Voegeli ’s experiments, this would mean modern men could get the same effect as reported with 116˚ from a reliably sustained 114˚ or 115˚. But whether or not this is the case, since even 110˚ produced four to seven months of infertility in Dr. Voegeli ’s tests, there seems to be significant room for lowering temperature to an individual comfort point below 116˚ if needed — especially given the substantially lower sperm counts of men today than men 60 years ago. Water at 110˚, which produced four to seven months of infertility, is not likely to be uncomfortable to any man, and 114˚ would be uncomfortable to very few.

Some might consider Voegeli's method inconvenient. However, it lasts six months, is separate from the sex act, appears to be safe and effective, and is readily available to all. Wet heat and all of the other heat-based contraceptive methods (with the exception of permanent ultrasound) are also easily reversible, nonsurgical, and reversible multiple times: all attractive features for a contraceptive.

For many years scientists greeted news of heat’s effects with great skepticism, probably not helped by the fact that Dr. Voegeli was female. Even researchers who did not dismiss the idea outright took pains with their word choice to show that they were not being gullible:

A seemingly drastic attack, but nevertheless of considerable interest, has been the study of heat influence on the testes… it is claimed that the method has been used successfully on nine volunteer subjects over a ten year period… Further, it is claimed that the method was put in practice in India between 1930 and 1950… This may sound fantastic, and in view of the fact that the report quoted contains no substantiating scientific evidence, one might be inclined to discount it summarily. However, recent investigations carried out on a scientifically controlled basis indicate that the heat treatment described would cause temporary male sterilization as claimed. In studies on men in the United States and Japan, the effect of heat on sperm production has been demonstrated very clearly. (Kiser, Milbank Memorial Fund., & Population Council., 1962)

In 1949, Voegeli began a 20-year campaign to publicize the heat method so that, if the results of further studies were favorable, the method could be widely used (Corea, 1985; Robinson, Rock, & Menkin, 1968). Voegeli’s impassioned pleas for the method make fascinating reading and show how in some ways, the plight of the poor has changed very little in the intervening 50 years. Her attempts to publicize this free contraceptive were generally unsuccessful, although in 1954 the Japanese government requested the information and conducted several successful experiments (Corea, 1985 ch. 9).

Though neglected as a contraceptive for humans, heat’s effects have long been studied in the veterinary and animal husbandry field. A senior researcher at Sydney University in Australia, who was given the 1997 Distinguished Andrologist award by the American Andrology Society, has gathered information on heat’s effects and has been publishing in the field since the 1960s (Setchell, 1998; Setchell & Thorburn, 1969; Waites & Setchell, 1964).

For humans, only when heat began to be recognized as a factor in unwanted infertility did it begin to receive greater research priority. By now the literature on heat is extensive. Studies have explained heat’s method of action (Hikim et al., 2003; Mann et al., 2002) and tested it in monkeys (Lue et al., 2002), while studies on occupational heat exposure have added further knowledge (Thonneau et al., 1998). Ever since 1988’s exhaustive review article in the respected journal “Fertility and Sterility” (Kandeel & Swerdloff, 1988), knowledgeable scientists can no longer be skeptical.

Ironically, simple wet heat has gained newfound respect in the past decade as it has been explored as a booster for hormonal male contraception (Lue et al., 2000). Respected scientists Drs. Christina Wang and Ronald Swerdloff of the University of California, Los Angeles have pursued this work despite little support from colleagues. However, no scientist has initiated systematic studies of the wet heat method based on Dr. Voegeli ’s formula.

The simple wet heat method currently in use by a few brave and dedicated men is not substantially different from what Voegeli developed in 1921, although various alternate combinations of temperature, time and heat source have been studied and in some cases patented. More research needs to be done in this area. For example, hot packs or heating pads may work instead of hot water, and treatment at a lower temperature with a booster treatment every three weeks may be effective (Kandeel & Swerdloff, 1988; Walston, 1991).

Wet heat remains a time-intensive method appropriate only for the most dedicated of men, yet in the past decade, the mechanics of it have become easier in prosperous countries. Various inexpensive, readily available small household appliances can be put to use for maintaining and confirming water temperature, and over-the-counter fertility tests are becoming more sophisticated. (For details on the types of tools available, click here.)

The tools are now available to make wet heat a fairly simple method. However, wet heat's implementation faces several challenges:

  1. Not enough research funds have been directed toward this method to accumulate the huge body of evidence of safety that is required for a method to be officially sanctioned.
  2. Research on it is not prestigious and often earns scientists derision from their colleagues.
  3. Since money can be made only from creative applications of the method (not from patenting the method itself), no large pharmaceutical firm will sponsor it.

All of these problems could be solved by backing and research efforts by government and not-for-profit agencies.

Artificial Cryptorchidism/ Suspensories

In the United States, among the few who picked up Voegeli's work were John Rock and Derek Robinson of Harvard University. Their work on the effect of insulated underwear (Robinson & Rock, 1967) and hot water (Rock & Robinson, 1965) on spermatogenesis forms the basis of a related method of contraception: artificial cryptorchidism, more commonly referred to as suspensories.

The idea of artificial cryptorchidism is simple. Researchers combined two pieces of information:

  1. Raising the temperature of the testes to body temperature (by using insulated underwear or hot water) results in subfertility; and
  2. Men with cryptorchid (undescended) or retractile testes are often infertile (Nistal & Paniagua, 1984).

By putting these two facts together, the pioneers in this area concluded that the testes can be raised to body temperature with less trouble than with insulated underwear by simply maintaining the testes close to the inguinal canal (the tube into which retractile testes withdraw) during waking hours (Mieusset et al., 1985).

Suspensory design
(a) testes in normal position; (b) testes raised to near inguinal canal;
testes held in place with (c) briefs with ring of soft rubber or
(d) ring alone. (adapted with permission from Mieusset & Bujan, 1994)

Drs. Roger Mieusset and Louis Bujan of France were the first to achieve effectiveness rates with artificial cryptorchidism that make it suitable for contraception (Mieusset et al., 1987). In Mieusset's method, during waking hours a man wears an under-brief that holds the testes snug against the body but doesn't enclose the penis.

When some of the men in his study refined the retaining underwear by adding a circle of soft material to keep the testes from moving away from the inguinal canal, effectiveness rates shot up, with an average sperm count of 3 million/ml and average motility of 15% (Mieusset et al., 1991), as opposed to values with the old method of 12 million/ml and 22-30% (Mieusset et al., 1987). Using a soft rubber ring was even better, with motile sperm counts consistently below 2 million/ml (average 0.12 million/ml) and the method being ready for contraceptive use sooner (generally within 2-3 months) (Mieusset & Bujan, 1994):

Average sperm count
Average motility
Average motile sperm count
12 million/ml 22-30% 3 million/ml
3 million/ml 15% 0.45 million/ml
- - 0.12 million/ml
Infertility diagnosis:
Below 10-20 million/ml 40-50% or below 4-10 million/ml or below

Since infertility is generally diagnosed when sperm counts fall below 10-20 million/ml and motility is below 40-50% (Makler, 1986; World Health Organization, 1999), the desired result is clearly being achieved. Starting in 1994 an additional five men used the technique for one to three years, with similar results (personal communication, Dr. R. Mieusset , Oct. 26, 2005).

The contraceptive effects of artificial cryptorchidism are reversible upon method discontinuation, with sperm counts returning to normal within 12-18 months (Mieusset & Bujan, 1994). Artificial cryptorchidism thus meets many of the criteria for an ideal male contraceptive: it is cheap, nonsurgical, nonocclusive, easily reversible, reversible multiple times, reversible nonsurgically, and separate from the sex act. It also appears to be effective and relatively convenient. However, large-scale tests of fertility return after long-term use would be reassuring. Short-term use (one to four years) appears to allow full return of fertility: the few tests in humans have all been favorable, as have tests of other heat methods in rats, dogs and monkeys (Kandeel & Swerdloff, 1988).

One concern regarding artificial cryptorchidism is potential cancer risk. Although nearly any proposed male method can be abandoned because of the suggestion that it might someday, somehow cause cancer, artificial cryptorchidism presents a more logical concern. Permanent, full-time, natural cryptorchidism since childhood is associated with increased risk of testicular cancer, although causation is not known (for example, both the cryptorchidism and the cancer are quite possibly the result of a third factor) (Giwercman, Muller, & Skakkeboek, 1988). Though artificial cryptorchidism is part-time rather than full-time, temporary rather than permanent, induced rather than from natural causes, and initiated in adulthood rather than childhood, these concerns will still be important to address.

On a more day-to-day level, many men fear that this method would cause the fungal infection commonly known as "jock itch." However, Mieusset's volunteers showed no signs of jock itch. A more likely limiting factor is that some men find the sensation of retracted testes uncomfortable, although most men don't mind or don't notice the sensation (Lissner, 2005b). No method will appeal to all men, so this should not hold back development of artificial cryptorchidism.

As for convenience, the only modification of habits required would be for men to wear slightly different underwear: briefs with an inner layer or ring for holding the testes (Mieusset et al., 1987). Since the materials are readily available, suspensories are already in use by some men. For example, after doing extensive research and making sure he felt comfortable with what is known and not known about artificial cryptorchidism, one man used himself as an experiment. He found that he could create the same effect as Mieusset’s special underwear by lifting the testes into position and then slipping an ordinary thick rubber band (i.e., the small blue type used on stalks of broccoli in supermarkets) around the scrotal skin (Jenks, 2004). He has been using testicular heating as contraception since 1998.

Though artificial cryptorchidism is clearly an effective method of contraception and is nearly free to the user, governments have not pursued it — and it is not likely to be pursued barring a change in the priorities of the international research community. Even the pioneers in this field, Drs. Mieusset and Bujan, are not able to attain the funding they need for further research. They hope to study the effects of artificial cryptorchidism on sperm DNA during and after treatment in order to more precisely evaluate the safety of the technique. Some of this work has already been done in rats, but not in humans (Tramontano et al., 2000). However, the funding for the technicians and the expensive diagnostic techniques has not been forthcoming (personal communication, Dr. R. Mieusset, Oct. 26, 2005). While awaiting funding, Mieusset and Bujan continue to publish about the deleterious effect of heat on fertility, and they seem to have found a more receptive audience in the infertility field (Thonneau et al., 1998).

Polyester Underwear

The polyester suspensory was similar to artificial cryptorchidism underwear but was looser and made of a different material. Its theoretical benefit over artificial cryptorchidism was the looser position of the testes, which would have allowed use by men who find the inguinal position uncomfortable.

Polyester suspensory research stemmed from a study that found that polyester underwear creates a greater "electrostatic potential" (i.e., more static electricity) than either cotton or half cotton/half poly underwear (Shafik, Ibrahim, & el-Sayed, 1992). Based on this, its developer concluded that the zero sperm counts obtained with polyester suspensories (i.e., a "jock strap" that holds just the testes) might be the result of both heat and static electricity across the testes (Shafik, 1992).

Many researchers reject this theory, saying that a static electricity field traveling all the way across the testes is not plausible, but speculate that Dr. Shafik 's findings could have been the result of an intensified heat effect, since polyester retains more heat. With the public’s interest in mind, several government agencies took the admirable step of planning a small study to answer these questions.

The study was conducted by Dr. Christina Wang at the University of California Los Angeles, a respected researcher. Dr. Wang did find a consistent small increase in temperature in the 21 men, but whether or not there was also an “electrostatic potential” effect, the end result was not enough to significantly affect sperm quality (Wang et al., 1997).

Some may argue that because the sling design was slightly different in Dr. Wang ’s study, hope for the method should not be abandoned. However, the original researcher has since published studies stating that unlike with cotton or wool underwear, men wearing polyester underwear had reduced potency (perhaps, the author speculates, because of electrostatic fields’ effect on intrapenile structures) (Shafik, 1996). Since a contraceptive that reduced potency would be highly unpopular, the approach is clearly dead.

Policymakers at the United States Agency for International Development (USAID), the World Health Organization, the National Institutes of Health, and the Contraceptive Research and Development Program are to be commended for proposing and funding Dr. Wang ’s study. Only by testing and confirming results can we learn which methods deserve further focus.

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