If it takes just one sperm and one egg to create a baby, why must men make so many sperm? And how many sperm are considered normal? How long do sperm live? Can they survive outside the body? Do men stop making sperm as they age? Is there anything you can do to increase sperm production or improve the health of your sperm?
WebMD takes a look at the facts about sperm and answers these and other frequently asked questions.
By Abigail Haworth
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The answer depends on a number of factors, the most important of which is where the sperm are located. On a dry surface, such as clothing or bedding, sperm are dead by the time the semen has dried. In water, such as a warm bath or hot tub, sperm will likely live longer because they thrive in warm, wet environments; however, the chances sperm in a tub of water will find their way inside a female bather and cause her to become pregnant are extremely low.
Inside a woman's body, sperm can live for up to five days depending on the conditions. If you have unprotected sex even a few days before your partner ovulates, there is a chance of achieving a pregnancy.
How many sperm do you need to achieve a pregnancy?
It takes just one sperm to fertilize an egg and achieve a pregnancy, but for each sperm that reaches and fertilizes an egg, there are millions that don't. The average ejaculation contains close to 100 million sperm; according to the World Health Organization, men who have fewer than 20 million sperm per milliliter of semen may be at risk for having infertility issues.
Why are so many sperm released if it takes only one to make a baby? To meet the waiting egg, the semen must travel from the vagina to the fallopian tubes, an arduous journey that few sperm survive. For those that complete the trip, penetration of the egg is far from a sure thing. The egg is covered by a thick layer that makes fertilization difficult. Experts believe this process may be nature's way of allowing only the healthiest sperm to fertilize the egg, thereby providing the best chances to produce a healthy baby.