You probably know from basic high school biology that one sperm and an egg will make a baby. But you might not know that sperm can only survive for a few minutes outside of the body, unless they’re ejaculated into a thick enough cervical mucus that helps them stay moist and warm.
Factors Affecting Sperm Survival
Sperm survival varies depending on the environment in which they are released. For example, sperm on dry surfaces like bed sheets or clothing will typically die within 15 to 30 minutes due to the lack of moisture, which is essential for their survival. When ejaculated sperm land on moist surfaces such as the skin of your partner or in a bath, they can survive longer since they thrive in warm, wet environments.
In the vagina, sperm can live up to five days in the protective, sperm-friendly cervical mucus. When a woman is in her fertile window, meaning the days leading up to and including the day of her ovulation, the thickness of the mucus barrier thins, allowing sperm to move freely through the female reproductive tract, cervix, and fallopian tubes.
The sperm-friendly pH levels of the vaginal fluid are also crucial for sperm survival. While the normal pH level of the vagina is slightly acidic and therefore hostile to sperm, during ovulation, this shifts to an alkaline pH level that can help increase sperm survival and fertilization rates.
To get pregnant, a man’s sperm must make it to the egg and fertilize it. This requires sperm to be able to swim through the seminal fluids that comprise the female reproductive tract, cervix, uterus, and fallopian tube. The ability to do this is known as sperm motility, and it can be impacted by factors such as health, age, diet, and how frequently a woman engages in sexual activity.
Cervical Mucus
Sperm can survive in a woman’s cervical fluid for up to five days, which means it is possible for sperm to get into her uterus and fertilize an egg. However, once sperm is exposed to air and becomes dry, such as on clothing, bed linens or toilet seats, they die very quickly. Similarly, sperm left in the water of a hot tub or warm bath will only survive for a few minutes before they are dead.
To survive, sperm needs warmth and moisture, which is why the cervical mucus is a sperm-friendly environment. The cervical mucus has a sticky texture that protects sperm while still allowing them to move around the body. The texture of the cervical mucus changes throughout a woman’s menstrual cycle, which allows her to track the right time for her ovulation. Knowing the right time for a fertile window (the few days leading up to and including the day of ovulation) is crucial for pregnancy success.
This is why many people believe that it’s possible to become pregnant from unprotected sex that took place during the woman’s fertile window. Unfortunately, it’s not that simple. In reality, for sperm to make it into the uterus and fertilize an egg they must first be ejaculated. Sperm can only survive in the vagina and uterus for up to five days, so it is highly unlikely that sperm that was ejaculated a few hours before ovulation will make it to the uterus in time to fertilize an egg.
pH Levels
Most sperm die within 24 hours of being released into the cervical fluid. But if the conditions are right, sperm can survive in the cervical fluid for up to five days, until they reach the fallopian tubes and the egg.
Women’s pH levels in the vagina are normally acidic, and this environment is optimum for sperm to swim in. When a woman’s fertility is high, her system produces a form of cervical mucus that allows this to happen. This forms a protective barrier that shields the sperm and facilitates their journey to the fallopian tubes.
But if sperm is exposed to room air on clothing, bed linens or toilet seats, it loses its motility and dies rapidly. And if it’s deposited into the vagina, it can also dry out and lose its ability to fertilize the egg.
The best way to prevent this is by using a condom whenever you have sex. This will protect you from STDs and prevent alkaline semen from disrupting the vaginal pH balance. You should also avoid douching and use a gentle soap for vaginal cleaning, and make sure you change your tampons every four to eight hours. Lastly, a healthy diet can help keep your vaginal pH balanced too. Try to eat plenty of fruits, vegetables, fish, whole grains and low-fat dairy.
Frequency of Sexual Activity
Sperm can only survive for a few minutes outside of the body. The environment in which they are released and their destination also affects how long sperm can live. In warm water, such as a hot tub or a bath, they will die quickly. But if they are frozen under ideal conditions, they can live indefinitely.
When a man is sexually aroused, millions of sperm mix with seminal fluid to create semen. This sperm is then discharged through the vas deferens and into the urethra for ejaculation. Most sperm die in the urethra, and the few that make it through are usually killed by natural barriers in the female reproductive tract, such as the abrupt constrictions of the cervix.
The sperm that does survive are then released into the fallopian tubes where they can swim to the egg and fertilize it. While the exact number of sperm that makes it to the egg can vary, it’s estimated that most pregnancies are a result of intercourse occurring during the “fertile window” between two days before and one day after ovulation.
While most people know that a sperm and egg must join to make a baby, many don’t understand the details of how this happens. Understanding the factors that influence sperm survival — from cervical mucus to pH levels — can help you optimize your chances of getting pregnant.
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