Why Are My Testicles Shrinking? Causes of Testicular Atrophy, From TRT to Varicocele

It is one of the questions men are least likely to say out loud, and one of the most searched for in private. You notice that your testicles seem smaller than they used to be, or that one is noticeably smaller than the other, and your mind goes straight to the worst possibilities.

Sometimes there is a simple, harmless explanation. Sometimes it is a sign of something worth fixing, and occasionally it needs a doctor the same day. This guide goes through the real causes of shrinking testicles, from the most common to the rare, what each one means for your testosterone and fertility, and how to tell which situation you are in.

First, what is normal?

Adult testicles vary a lot in size. Doctors measure them by volume, either by comparing them with a string of graded beads called an orchidometer or with an ultrasound scan. A typical adult testicle is somewhere around 15 to 25 ml, roughly the size of a walnut to a small plum. Below about 12 ml is generally considered small.

It is also completely normal for the two to differ. The left one usually hangs a little lower, and one is often slightly larger. What matters is change: a testicle that has become noticeably smaller, softer or different from how it used to feel.

Not every change is shrinkage

The scrotum changes shape all day. In cold weather, in cold water, after exercise or when you are anxious, a muscle in the scrotal wall pulls the testicles up tight against the body so they look and feel smaller. In a warm shower they drop and look bigger. This is how the body keeps them at the right temperature, and it has nothing to do with true shrinkage.

Real testicular atrophy is a reduction in the size of the testicle itself, and it usually feels softer as well as smaller.

Why size is mostly about sperm, not testosterone

This is the single most useful thing to understand. Most of the volume of a testicle is made up of long, coiled tubes called seminiferous tubules, where sperm are made. The Leydig cells that produce testosterone sit in the small spaces between those tubes and take up only a fraction of the space.

So when a testicle shrinks, it is usually because sperm production has dropped. Testosterone may or may not be affected, depending on the cause. Small testicles can mean low fertility with normal testosterone, low testosterone with low fertility, or occasionally neither. Working out which needs a blood test and sometimes a semen analysis.

The common causes

1. Testosterone therapy and anabolic steroids

This is one of the most common reasons for both testicles to shrink in men under 50. When you take testosterone from outside the body, whether prescribed TRT or steroids bought online, your brain detects high levels and switches off the signals it normally sends to the testicles: luteinising hormone (LH) and follicle-stimulating hormone (FSH). Without them, the testicles stop making both testosterone and sperm, and they shrink, often by a noticeable amount within a few months.

This is expected, not a sign that something has gone wrong with the treatment. But it has two important consequences. First, TRT stops sperm production in most men, so while it is not a reliable contraceptive, it makes conception much less likely. Second, after stopping, the testicles need time to restart.

Men who want to keep testicular size or fertility on TRT are sometimes given hCG, a hormone that mimics LH and keeps the testicles working. Our guides to TRT side effects and to anabolic steroid side effects cover this in more detail.

Will they go back to normal?

Often, yes, but not always, and not quickly. After stopping testosterone or steroids, recovery of the hormone signal can take several months, and sperm production takes longer, because each cycle of sperm takes around 74 days to mature. The longer and heavier the use, the slower and less certain the recovery. Our article on testosterone recovery after steroids explains what is involved.

2. Varicocele

A varicocele is a group of swollen veins in the scrotum, similar to varicose veins in the legs. It affects around 15% of men and is much more common on the left. It often feels like a soft lumpy bag, sometimes described as a bag of worms, above the testicle, and it may ache after standing for a long time.

Varicoceles warm the testicle and can slowly reduce its size and sperm production. In teenagers, a testicle on the varicocele side that is falling behind in growth is one of the main reasons doctors recommend treatment. In adults, it is linked with lower sperm counts and, in some men, lower testosterone. Our full guide to varicocele and testosterone covers when repair helps.

3. Ageing

Testicles become a little smaller and softer with age, alongside a gradual fall in testosterone and sperm production. This is usually modest and happens slowly over decades. A sudden or one-sided change should not be put down to age.

Causes that need attention

Mumps orchitis

Mumps in childhood rarely affects the testicles, but in teenagers and adult men it causes painful testicular swelling, known as orchitis, in a sizeable minority. In some of those men, the affected testicle later shrinks, sometimes permanently. When both sides are affected, fertility can be reduced. Mumps outbreaks still happen in young adults who missed the MMR vaccine, which is a good reason to check your vaccination if you are not sure.

Torsion: the one that cannot wait

Testicular torsion is when a testicle twists on its cord and cuts off its own blood supply. It causes sudden, severe pain, often with swelling, nausea and vomiting, and it is most common in teenagers and young men, though it can happen at any age.

The testicle can usually be saved if it is untwisted within about six hours. After that, the chance falls quickly, and a testicle that has lost its blood supply will shrink and may need to be removed. Sudden severe testicular pain is an emergency. In the UK go to A&E or call 999; in the US go to the emergency room or call 911. Do not wait to see if it settles.

Injury

A hard blow to the testicles, from sport, a fall or an accident, can damage the testicle and its blood supply. Most minor knocks heal completely, but significant injuries can lead to shrinkage later. Any injury that causes swelling, bruising or pain lasting more than an hour should be checked.

Cancer treatment

Chemotherapy and radiotherapy can damage the cells that make sperm and, less often, testosterone. Men who have had treatment for testicular cancer, or for other cancers in the pelvis, may notice smaller testicles afterwards. Our article on testicular cancer and testosterone explains what happens to hormones after treatment.

Testicular cancer itself more often causes a lump or a testicle that feels firmer and heavier, rather than smaller. Any new lump should be checked by a doctor, even if it is painless.

Rarer causes worth knowing about

• Klinefelter syndrome. Men born with an extra X chromosome typically have small, firm testicles, often under 4 ml, along with low testosterone and very low sperm counts. Many are not diagnosed until adulthood, often during fertility tests. See Klinefelter syndrome.
• Pituitary problems. A pituitary tumour, a raised prolactin level or damage after a head injury can cut the hormone signal to the testicles.
• Iron overload. Haemochromatosis can deposit iron in the pituitary and lower the signal to the testicles.
• Heavy drinking and liver disease. Long-term heavy alcohol use and cirrhosis damage the testicles directly and raise oestrogen, both of which can lead to shrinkage.
• Oestrogen and some medicines. Oestrogen treatments, some prostate cancer drugs and long-term opioid use can all lower the hormones that maintain the testicles.
• An undescended testicle in childhood, even after surgery, may stay smaller.

How a doctor works out the cause

A GP or urologist will usually start with a few questions: when you noticed the change, whether it is one side or both, any pain, injury, mumps, medicines, supplements, testosterone or steroid use, and whether you are trying for children. Be honest about steroids. Doctors are not there to judge, and it changes the whole interpretation of the tests.

Then come:

• An examination, sometimes with an orchidometer to measure size
• An ultrasound scan, which measures volume accurately and checks for varicocele, lumps and blood flow
• Early morning blood tests: total testosterone, LH, FSH, and often prolactin and SHBG
• A semen analysis if fertility is a concern

The blood test pattern is what separates the causes. If testosterone is low and LH and FSH are high, the problem is in the testicles themselves, as in Klinefelter syndrome, mumps or past injury. If LH and FSH are low, the problem is the signal from the brain, which is what happens with TRT, steroids, pituitary problems and some medicines. For reference, UK specialist guidance treats a total testosterone below 12 nmol/L (about 350 ng/dL) as possibly low. Our guide to reading blood test results explains the rest.

When to see a doctor

Same day, emergency: sudden, severe pain in a testicle, with or without swelling or vomiting.

Within a week or two: a new lump or hard area, a testicle that feels heavier, or a visible change in size or shape in one testicle.

Routine appointment: a gradual change in size on both sides, especially with low sex drive, tiredness or fertility problems; shrinkage after stopping steroids or TRT that has not improved after several months.

The bottom line

Testicles that look smaller in the cold are normal. Testicles that have truly shrunk are telling you something, most often that the hormone signal from your brain has been switched off by testosterone or steroids, or that sperm production has been damaged by a varicocele, infection or injury.

Because testicle size mostly reflects sperm production, shrinkage is first of all a fertility question, and only sometimes a testosterone one. A simple ultrasound and an early morning blood test usually make the cause clear. Get sudden pain seen immediately, get any lump checked promptly, and do not let embarrassment stop you asking.

Common questions

Can testicles shrink and then grow back?

Yes, when the cause is reversible. After stopping TRT or anabolic steroids, size often recovers over several months as the hormone signal returns, though heavy or long-term use can slow or limit recovery.

Does a smaller testicle mean low testosterone?

Not necessarily. Most of a testicle's volume is sperm-producing tubes, so shrinkage usually reflects lower sperm production first. A blood test is the only way to know whether testosterone is affected.

Is it normal for one testicle to be smaller?

A small difference is very common and normal. A testicle that has become noticeably smaller or softer than it used to be should be checked, as varicocele, past infection or injury are possible causes.

Does TRT always shrink the testicles?

Most men on testosterone therapy notice some shrinkage, because the brain stops sending LH and FSH. Some doctors add hCG to keep the testicles working, particularly in men who want children.

Can a varicocele make a testicle shrink?

Yes. A varicocele can slowly reduce the size of the testicle on that side, which is one of the main reasons for repairing it in teenagers.

Sources: Sakamoto H et al., Testicular volume measurement: comparison of ultrasonography, orchidometry, and water displacement, Urology 2007;69(1):152-7 · Patel AS et al., Testosterone is a contraceptive and should not be used in men who desire fertility, World J Mens Health 2019;37(1):45-54 · Kohn TP et al., Age and duration of testosterone therapy predict time to return of sperm count after hCG therapy, Fertil Steril 2017;107(2):351-7 · European Association of Urology, Guidelines on Sexual and Reproductive Health (varicocele, hypogonadism) · Masarani M et al., Mumps orchitis, J R Soc Med 2006;99(11):573-5 · NHS, Testicular torsion · Educational only, not medical advice.

Keep reading: Varicocele and testosterone · Will TRT make you infertile? · Sperm count: what lowers it · Klinefelter syndrome · Testosterone recovery after steroids · Testicular cancer and testosterone