A number of factors can play a decisive role in some couples' inability to conceive, which may lead them to turn to fertility treatments like IVF or IUI.

But before couples get to that point, they often seek advice from specialists. In women common infertility issues are associated with ovulation disorders, fallopian tube damage or inhospitable conditions of the uterus, according to Mayo Clinic. 

In men, most infertility issues are associated with vitality and quantity of sperm produced; and whether those sperm will live long enough or experience issues while trying to reach an egg within the female reproductive tract. "All sperm are not equal and even in men with proven fertility, it is common for nearly half of sperm to be dead when they're ejaculated," explains Timothy Moss, an associate professor of obstetrics and gynecology at Monash Health in Australia. "There are numerous health conditions that affect the viability of sperm, their ability to move, or even whether they are produced at all," he adds. 

It can be helpful to understand what some of these conditions are and for how long sperm can generally be expected to live. 

What is sperm?

The first thing to understand is that despite the words "sperm" and "semen" often being used interchangeably, they are actually different things. "Semen is a cocktail produced at the time of ejaculation that consists of sperm (produced in the testes) and fluid from the prostate and seminal vesicles," explains Dr. Paul Turek, a men’s fertility physician and the director of the Turek Clinic in San Francisco.

The sperm portion of that consists of developed or mature male sex cells that can fertilize a mature female sex cell - called an ovum or an egg, explains Moss. "A normal semen volume starts around 1.5 milliliters and a normal sperm count is somewhere between 12 and 16 million sperm per milliliter of semen," he adds. 

What is the main function of the sperm?

Like other cells in the body, sperm cells are produced and developed with a specific objective or design. "Sperm are highly specialized cells that have one purpose: to deliver genetic information from a male parent into the egg of a female parent," says Moss. 

Turek says semen helps sperm fulfill this function in two ways: by helping sperm cells propel themselves to where they need to be within the female reproductive tract, and by "keeping the sperm healthy, energized and buffered from the surrounding hostile vaginal fluid."

How long does sperm live?

Once sperm is deposited during sexual intercourse, "sperm can survive from 1-2 days," says Turek. In some cases, motile sperm can survive within the female reproductive tract for up to 5 days, "but the work environment needs to be ideal for them to do their job successfully," he says.

Most sperm won't live long enough to do so, however. Moss says that most sperm die "within about 12 hours," so it's only a small percentage of them that remain viable long enough for conception to occur.

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