In another 10 percent, factors in both the man and woman contribute to infertility. Problems with sperm production result in a reduced sperm count. A reduced sperm count may be caused by a number of factors, including hormonal changes, medications, drug use, alcohol use, excessive caffeine, cigarette smoking and testicular injury. These same factors might also cause a lowered motility.
Motility is determined by the percentage of sperm that are moving or swimming.
Sperm motility is also affected by temperature. If the testicles are too warm, the sperm motility and possibly the sperm count may be reduced. Increased scrotal temperature may be caused by use of waterbeds, hot tubs and saunas, as well as wearing tight underwear and tight pants. Increased numbers of abnormal sperm may also result from medications, drugs and alcohol, as well as testicular injury, and environmental exposure to chemicals or heavy metals. It is generally thought that these abnormal sperm are not capable of fertilization.