An experimental male contraceptive method involves heating the testicles so that they cannot produce sperm. Sperm are best produced at a temperature slightly below body temperature. The muscles around a male's scrotum involuntarily tighten if the man's body temperature drops, and they loosen, allowing the testes to hang, if the body temperature rises. This is the body's way of keeping the sperm at an ideal temperature. Although research has not addressed methods of applying heat, sperm production can be disrupted with increased temperature. Some suggest exposure to high temperatures (116°F) can affect fertility for months.
Methods used include hot water applied to the scrotum, heat generated by ultrasound, and artificial cryptorchidism (holding the testicles inside the abdomen) using specialized briefs. Initial experiments suggest it is effective, safe, and reversible, though there have not been long-term studies to determine if it has any side effects on the body or quality of sperm after reversal. The optimal heat level and time period of exposure are not known.
One method under investigation is ultrasound, which involves the application of high-frequency sound waves to animal tissue, which in turn absorb the sound waves’ energy as heat. The possibility for ultrasound’s use for contraception is based on the idea that briefly heating the testes can halt sperm production, leading to temporary infertility for about six months. Additionally, ultrasound could affect cells’ absorption rates of ions, which itself could create an environment unfavorable to spermatogenesis. Its extremely localized effects on animal tissues make ultrasound an attractive candidate for research, but so far studies have only been performed on non-human animals, such as dogs.