Scientists are warning that heatwaves could be contributing to a global decline in male fertility, as research suggests sperm quality is worsening worldwide. A study published in 2022 found that average sperm counts fell by 1.2% per year between 1973 and 2018, from 104 to 49 million per millilitre of semen. Experts say that below 40 million per millilitre, fertility problems become more likely.
Male infertility now accounts for about half of all infertility cases and affects 7% of men, yet it remains under-discussed due to social stigma. For many men, the cause of their fertility problems is unexplained, leaving them suffering in silence. Factors such as pollution and rising temperatures are increasingly being linked to declining sperm quality.
Sarah Martins Da Silva, a clinical reader in reproductive medicine at the University of Dundee, described sperm as 'exquisite cells' that are highly specialised. She noted that even small changes can affect their ability to fertilise an egg. Key aspects of sperm health include motility, morphology, and count.
One couple from Yorkshire, Jennifer and Ciaran Hannington, experienced the emotional toll of male infertility firsthand. After trying for a baby for two years, tests revealed Ciaran had a low sperm count and poor motility. He described feeling 'shock, grief, and denial', and said he felt he had let his wife down. His mental health deteriorated, leading to panic attacks and alcohol use.
While global population growth has slowed due to social and economic factors, researchers warn that declining fecundity—the physical ability to reproduce—may also be playing a role. Rising rates of testicular cancer, erectile dysfunction, and low testosterone in men suggest a broader reproductive health crisis that could have significant societal impacts.
