Everyone uses a mobile phone these days, so it is difficult to realise that twenty five years ago they were rare and expensive items. Unfortunately, mobile phone use has crept up on the human race with such stealth we have not yet had a chance to think through the health implications fully. It is likely that we will need at least one generation and perhaps two to grow up using mobiles from childhood to old age, before we fully understand the risk that these devices pose.
The risk from mobile phones comes from the microwave radiation that they emit. The trouble with assessing the impact of radiation exposure is that it is only after a lengthy period of time that any side effects will become apparent. Just how long that time period is depends. But for the development of cancer, for example, it could be several decades.
For other side effects, the process can be faster. We know that daily exposure to mobile phone radiation causes men to produce fewer sperm, and poorer quality sperm. This only requires exposure over a period of weeks, not years. But whether this effect eventually causes cumulative damage on top of the reduction in fertility, is not yet clear.
It is precisely because of the uncertain impact of the radiation that mobiles emit, and the realisation now that they cause infertility, that it has become important for men in particular to keep their mobile phone in an anti-radiation phone case.