The production of sperm can be disrupted with a rise in temperature. Male thermal contraceptive methods (MTCs) involve heating the testicles inside the scrotum so that sperm production is slowed down. MTCs induce temporary infertility in men via a number of different methods, including applying hot water to the scrotum, generating heat on the testicles using ultrasound or heating pads, and creating artificial cryptorchidism (i.e., holding the testicles inside the abdomen) using specialized underwear.
The cremaster muscle is located between the internal and external layers of spermatic fascia, and thus it covers the testicles. It works involuntarily and its role is to lower the testicles if the scrotal temperature rises or to raise them closer to the body if the scrotal temperature drops. This process allows the muscle to regulate the temperature of the testicles in order to keep it several degrees lower than that of the body, which enables an ideal environment for spermatogenesis. When the temperature of the testis is raised, other effects in sperm have also been observed, such as a decrease in motility and an alteration in the structural characteristics of the spermatozoa that are produced. Some suggest that exposure to high temperatures (47 °C) can affect fertility for months, and one of the initial experiments resulted in partial infertility lasting more than four years.
These initial explorations into MTCs suggest it could be effective and safe, though there have not been sufficient long-term studies to determine if there are any side effects on the body after reversal, nor any indication in terms of how long any side effects may persist. The limited amount of research into these methods limits our collective understanding of the safety and efficacy of MTCs. Despite this, there is growing interest in these as next generation non-hormonal, reversible male contraceptives.
Male Contraceptive Initiative is investing in developers working on these methods in order to address this lack of research and to help ensure there is a diverse method mix for men and their partners in the future.