While tight underwear may slightly increase testicular temperature, current research does not strongly link them to infertility.

The testicles function best at a temperature slightly lower than body temperature, which is why they are located outside the body in the scrotum. Some studies suggest that prolonged exposure to heat (e.g., hot baths, saunas, or frequent laptop use on the lap) may impact sperm quality, but the effect of underwear alone appears to be minimal.

For optimal fertility, lifestyle factors such as a balanced diet, regular exercise, and avoiding smoking or excessive alcohol have a much greater impact than the type of underwear worn.