Why your heated car seat could be lowering your sperm count

Brass monkeys beware. When the mercury drops, some of the most common comforts we turn to in order to stay snug may be having a detrimental effect on male fertility.

Winter warmers such as heated car seats, electric blankets, saunas and even thermal underwear could be playing havoc with the crown jewels, warn experts.  

That winter could be bad for male fertility flies in the face of some research. While humans are not seasonal breeders, studies have found differences in sperm counts, with an average 30 per cent reduction in sperm counts in summer compared with winter. The science is not conclusive, however, and persistent cold could also be a problem – another study found that long-term exposure to cold could induce sperm DNA injury, although it does not affect sperm quality.

Problems arise when heat is applied to the testes indirectly through a range of winter devices. The testes work best when they are two to four degrees below body temperature. Any significant increase in testicular temperature for a prolonged period can damage sperm and reduce sperm count, meaning many of our favourite winter warming techniques could be out of bounds for men concerned with fertility.

Dr Jonathan Ramsay is a consultant urologist who deals exclusively with male fertility. He explains: “The testicles function optimally at temperatures of 32.5 degrees, because we were designed to run around naked. So, if you are sitting on a heated car seat wearing tight thermal underwear it’s going to be like sitting in a hot bath, which is not good. As a rule, uncommonly hot and uncommonly cold are not ideal. Winter is not a good season for sperm.”

Heated car seats

Warming up your back and posterior with a heated seat on the way to work on a frosty morning is one of life’s luxuries. But stewing your privates in your Peugeot for any prolonged period may not be doing your sperm count any favours.  

Dr Channa Jayasena, clinical senior lecturer at Imperial College London and consultant in reproductive endocrinology and andrology at Hammersmith and St Mary’s hospitals, explains: “Anything that heats up your testes for a sustained period is going to be bad for them. If you are driving very long distances using a heated car seat that makes your groin very hot for several hours, it will undoubtedly have an effect on your fertility.

“While we don’t have many direct studies on car seats, we do know how the testes work and we know that for brief periods there shouldn’t be a problem. Most men don’t use heated car seats in that way, so they are fine. But if you use one for hours and if you have contributing factors – if you are overweight, if you smoke, if you drink alcohol excessively, these things pile up.”