Mobile phones emit radio frequency electromagnetic waves. These waves could have certain detrimental effects on the nervous or cardiovascular system, but also on male fertility.
The radiation emitted by mobile devices can lead to an increase in reactive oxygen species (ROS) and thus oxidative stress. Oxidative stress has negative effects on male fertility by increasing sperm DNA fragmentation and affecting sperm motility.
On the other hand, mobile phone use may also lead to a decrease in testosterone levels, as Leydig cells are affected.
However, more research is needed to clarify the actual mechanism by which this type of radiation may affect male fertility.