Everything you need to know about sperm

Reviewed by our clinical team

Half the people on our planet have bodies that produce sperm – but lots of us don’t really know how it works!

If you’d like to be more clued up about what sperm is, how much the average man has, and how it leads to pregnancy, read on for our answers to some frequently asked questions.

What do sperm do?

Let’s start with the basics! Sperm are male reproductive cells which are made and stored in the testes (testicles or ‘balls’) and released during ejaculation.

When a man has sex with a woman and ejaculates into her vagina, the sperm will travel up through the cervix (neck of the womb) through the uterus (womb) and into the fallopian tubes. If the timings are right, the sperm can fertilise an egg and begin the process of pregnancy. Chromosomes carried in the sperm will determine genetic characteristics and the sex of the baby. 

What do sperm look like?

Sperm have a distinctive tadpole shape, with a bulbous “head” and a narrow “tail”. They only measure about 0.05mm long, which means they’re far too small to be seen by the naked eye.

Semen – the substance that carries sperm – is normally cloudy white, or sometimes grey, with a slippery, jelly-like texture. It contains alkaline fluids, which protect the sperm in the acidic environment of the vagina – because of this it has a bleach-like smell.

If your semen (‘cum’) looks yellow or green, or has a strong, unusual smell, this can be a sign of a sexually transmitted infection – it would be a good idea to get tested for STIs.

Where are sperm produced?

Sperm are made and stored in the testes (testicles), although they also spend some time in a narrow tube connected to the testes called the epididymis.

Just before you ejaculate, sperm gets pumped from the epididymis through another tube (the vas deferens) and into the urethra (the same tube that carries urine out of your body). Along the way, the seminal vesicles and the prostate gland release the alkaline fluids which protect the sperm in the vagina. 

How many sperm are produced every second?

Once you’ve been through puberty, your testicles will start producing at least 1,000 sperm every single minute – so about 17 every second. 

How fast can sperm travel?

At the point of ejaculation, sperm are travelling pretty fast – around 28 miles per hour! Once inside the vagina they can move very quickly. Within five minutes of ejaculation, your sperm may have already reached the fallopian tubes. 

How long do sperm live in the body?

It may come as a shock but sperm can survive within the female reproductive system for a week. However, this is more likely if sex happens during the fertile part of your partner’s menstrual cycle, around the time the egg is released.  

Can you run out of sperm?

No, you can’t run out of sperm. Your testes are always making new sperm, which means you’ll have a constant supply even if you’re masturbating a lot and/or having sex every single day. 

Having said that, it is possible to have a “dry orgasm”. This is where you reach a sexual climax, but don’t ejaculate any semen. In younger men, this is normally a sign that your genitals have temporarily run out of seminal fluid. In older men, it might be a sign of retrograde ejaculation. 

How do I know if I have a low sperm count?

The only way to know if you have a low sperm count is to get a fertility test. The NHS recommends that you do this if you’ve been trying to conceive with your partner for at least a year, and haven’t had any success. In this instance, your partner should also get a test.

Your GP can arrange a semen analysis test. They will tell you how and when to produce the sample. You will need to ejaculate into a container and get the sample to the hospital or clinic immediately, ideally within 30-60 minutes. Because this not possible for most people, you will usually be asked to produce the sample on site in a private room. After that, you might be referred to a fertility clinic for help. 

Get help with your sex life from Online Doctor

Problems with erections and ejaculation are surprisingly common amongst men of all ages.

If you’re worried that you’re ejaculating too quickly or if you’re struggling to get erections sufficient for sex, it’s a good idea to see your GP so they can work out the cause. You can also get help from Online Doctor – visit our erectile dysfunction or premature ejaculation clinics to find out more.

References

https://www.menshealthforum.org.uk/size-isnt-everything
https://www.nhs.uk/conditions/low-sperm-count/
https://www.nhs.uk/conditions/ejaculation-problems/