The scrotum keeps the testes' temperature a few degrees below body temperature. If it gets overheated or constricted, sperm production slows down and can even stop. Despatch riders tend to have lower sperm counts. Breathing in toxic fumes and sitting for hours in tight leather clothing can overheat the testicles. Toxins in cigarette smoke damage sperm.
Smoking also lowers testosterone levels, affecting the development of sperm.
A study at the University of Birmingham found that children whose fathers smoked more than 20 cigarettes a day had a 30 per cent higher risk of developing cancer. Alcohol interferes with testosterone secretion, reducing sperm production and decreasing male sex drive. An estimated 40 per cent of male fertility problems are linked to alcohol. Zinc and selenium play a major role in protecting sperm. Zinc also helps 'fuel' the sperm's journey towards the egg.