Because they lie outside of the body, the testis are cooler than other organs, a condition that is important to sperm survival; conversely, heat is toxic to sperm production. The scrotal sac normally keeps the testes at a temperature of between 94 and 96 degrees Fahrenheit. At temperature above 96 degrees F, sperm production is greatly inhibited or stopped completely. Typically, the mean scrotal temperature of infertile men is significantly higher than fertile men. Reducing scrotal temperature in some men will be enough make them fertile.
Medical opinion is divided on how important the following are – soaking in a hot bath, Jacuzzi or sauna; long hours of sitting; using a laptop on the lap. In addition, the following exercises can raise scrotal temperature: rowing machines, simulated cross-country ski machines, treadmills, cycling and jogging.