When it comes to conceiving a child, there are lots of things that can go wrong—sperm allergies, poor egg quality, and ineffective sperm. Of the approximately 1 in 10 couples who are infertile, it has been estimated that male factors alone contribute to 30% of these cases.

Though men produce millions of sperm a day (compared to the 300–400 eggs that women release during their lifetime), external factors (like temperature) can affect the health of these little swimmers. And because sperm cells take about 75 days to grow to maturity, harming them can affect your fertility.

Here are 10 surprising factors that may affect a man’s sperm.

• Overheating

• Hot tubs

• Laptops

• Briefs

• Varicose veins

• Cell phones

• Obesity

• A party lifestyle

• Blockages& Genetic disorders

• Other detrimental factors