Low sperm count: causes and what to do next.

A sperm count is called low when it falls under the World Health Organization's 2021 lower reference limit of 16 million sperm per mL, or 39 million in the whole sample. That limit is the 5th centile of men whose partners conceived within a year, so it marks the bottom of the fertile range rather than a line between fertile and infertile: a 2001 New England Journal of Medicine study of 1,461 men (765 from infertile couples and 696 from fertile couples) found extensive overlap between fertile and infertile men on every measure. Roughly 30 to 40% of low counts have no identified cause, and the most common ones that do are varicocele (found in 35 to 40% of men seen for infertility), hormonal problems, genetic causes, and testosterone or anabolic steroid use. The changes with the best evidence are stopping smoking, getting to a healthy weight if you carry extra, and stopping any testosterone or steroids. NICE advises repeating an abnormal test about three months later, and sooner if no sperm or very few were found.

What counts as a low sperm count

Your report is compared against the WHO's 6th edition reference limits, published in 2021 and drawn from more than 3,500 men across 12 countries whose partners took a year or less to conceive. Two lines describe how many sperm there are:

• Sperm concentration: 16 million per mL. How crowded the sample is.
• Total sperm number: 39 million per ejaculate. Concentration multiplied by volume, and the more useful of the two, because a large sample of dilute semen can hold plenty of sperm.

The rest of the report has its own limits: volume 1.4 mL, total motility 42%, progressive motility 30%, vitality 54%, normal morphology 4%. The UK's NICE guideline lists the same set, plus a pH of 7.2 or above. The semen analysis guide goes through every line, and the checker compares your numbers with the limits. The morphology guide covers the line men worry about most.

The words a clinic may use come from the European Association of Urology's guideline rather than from WHO, which dropped most of them in 2021:

• Oligozoospermia: under 16 million per mL.
• Severe oligozoospermia: under 5 million per mL.
• Azoospermia: no sperm found at all, confirmed after spinning the sample down.

A result under the limit is not a diagnosis

This is the part most pages skip. The WHO manual says the percentiles "do not represent distinct limits between fertile and subfertile men", and makes the point that a semen analysis on its own is not prognostic: it is the fertility of the couple together that decides the outcome. The American Urological Association puts it the same way: values above or below the limit "do not by themselves predict either fertility or infertility". The 2001 study that compared fertile and infertile men directly concluded that "none of the measures, however, are diagnostic of infertility".

Two practical consequences. First, one test is not a result: NICE says an abnormal first analysis should be repeated. Second, a count a little under 16 million tells you much less on its own than it does alongside motility and volume, which is why clinics combine the three into a total motile sperm count.

How common is this

In the WHO's multi-country study of 8,500 couples across 25 countries, infertility was due to male factors alone in 18.7% of cases, to both partners in 26.3%, to female factors alone in 30.6%, and no cause was found in 10.8%. On those numbers a male factor contributed wholly or in part to 45.1% of cases. The AUA's guideline gives a similar split: solely responsible in about 20% of couples, contributory in another 30 to 40%. So a low count is roughly as likely to be part of the picture as anything on your partner's side, and it is very often not the whole picture.

What causes a low sperm count

In a series of 12,945 men seen for infertility, the European Association of Urology recorded no identified male cause in 30% of cases, varicocele in 14.8%, hypogonadism in 10.1% and undescended testes in 8.4%. The guideline's summary is that "in 30 to 40% of cases, no male-associated factor is found". That is worth saying plainly: unexplained is the single largest category, and it is not a failure of the testing.

The causes that are found group like this.

• Varicocele. Enlarged veins in the scrotum, present in about 15% of men generally, 25% of men with an abnormal semen analysis, and 35 to 40% of men seen for infertility. Thought to work partly through heat.
• Hormonal. Hypogonadotropic hypogonadism, where the signal from the brain to the testes is missing, is one of the few causes with a treatment that works well: NICE says to offer gonadotrophin therapy for it. Raised prolactin is also checked for.
• Genetic. Klinefelter syndrome (an extra X chromosome) is found in 13.7% of azoospermic men and 2.6% of unselected men seen for infertility. Y chromosome microdeletions are found in 8 to 12% of men with azoospermia and 3 to 7% of men with oligozoospermia, almost all of them under 5 million per mL. This is why NICE asks for a Y microdeletion test at a concentration under 1 million per mL, and a karyotype for unexplained azoospermia.
• Obstruction. A blockage, including after a vasectomy, means sperm are made but do not reach the ejaculate. NICE offers surgical correction or sperm retrieval for obstructive azoospermia.
• Medication and drugs. Testosterone and anabolic steroids are the big ones and have their own section below. Chemotherapy and radiotherapy suppress sperm production, often for one to four years. Sulfasalazine lowers semen quality, and semen improved in the original case series after it had been stopped for more than two months. Finasteride, at the 1 mg dose used for hair loss, has mixed evidence; the testosterone guide covers the studies. Long-term opioid use suppresses the hormonal axis: a 2020 meta-analysis of 3,250 patients found hypogonadism in 63%.
• Infection. Treatable when there is one, but NICE advises against antibiotics for white cells in the semen unless an infection is actually identified, because there is no evidence it improves pregnancy rates.
• Lifestyle. Smoking, weight, heat and heavy drinking, covered next.

What the evidence says helps

Ranked by how good the evidence is, not by how often you see it recommended.

Stopping smoking. A 2016 meta-analysis of 20 studies and 5,865 men found smokers' sperm counts were 9.7 million per mL lower (95% confidence interval 6.1 to 13.3 lower), with motility 3.5 points lower and morphology 1.4 points lower. The gap was larger in heavier smokers and in men already being seen for infertility. NICE notes the association while saying the effect on fertility itself is uncertain. The smoking and vaping guide has the detail.

Getting to a healthy weight. A meta-analysis of 21 studies and 13,077 men found the odds of a low or absent sperm count rose with BMI: 1.11 times for overweight men, 1.28 times for obese men and 2.04 times for morbidly obese men. Better than that association, a 2022 randomized trial followed 56 men through a low-calorie diet: their weight fell by an average of 16.5 kg, and sperm concentration rose about 1.5 fold and total count about 1.4 fold. The gains held at 52 weeks in the men who kept the weight off, and not in the men who regained it. Note what the trial measured: semen numbers, not pregnancies. The weight guide covers the rest.

Keeping alcohol within the guidelines. NICE's position is that excessive drinking is detrimental to semen quality, and that staying within the UK's 14 units a week, spread across several days, is unlikely to affect it. The alcohol guide has the dose curve.

Keeping heat off. NICE records an association between raised scrotal temperature and reduced semen quality, while saying it is uncertain whether loose underwear helps. A small experiment is the clearest picture we have: 10 men who took two 15-minute saunas a week for three months had a strong drop in count and motility, and the effect was completely reversed six months after they stopped. Ten men is ten men, but the reversal is the useful part. The heat guide covers saunas, hot tubs, laptops and cycling.

Cannabis is genuinely unclear. A 2021 meta-analysis found the relative risk of any abnormal semen parameter among cannabis users was 1.16, with a confidence interval from 0.84 to 1.60 that comfortably includes no effect. The authors would not rule an effect out either, given how few and how varied the studies were. Anyone telling you the answer is settled in either direction is ahead of the evidence. The cannabis guide goes through the studies.

Testosterone and anabolic steroids

This is the one cause where the fix is unambiguous and the advice often goes the wrong way. Testosterone taken from outside the body switches off the signal that drives sperm production. NICE is blunt: "do not offer androgens to treat semen abnormalities". The AUA guideline says clinicians should not prescribe testosterone to a man interested in current or future fertility at all.

Recovery is usual but slow. The best data come from an analysis of 30 trials of testosterone-based male contraception: the median time for sperm to return to 20 million per mL was 3.4 months, with 67% of men back at that level by 6 months, 90% by 12 months and effectively all by 24 months. Two honest caveats. Those were supervised, time-limited, physiological doses in healthy volunteers, which is not the same as years of high-dose steroid use. And in a series of 66 men who became infertile after taking testosterone, 30% still had a total motile count under 5 million a year after stopping, even with hCG and a selective estrogen receptor modulator to restart production; older men and longer users took longest. So: expect recovery, expect it to take many months, and do not treat it as guaranteed. The testosterone and fertility guide goes through the options for men who need treatment for low testosterone and want to keep their fertility.

Varicocele: worth treating, within limits

The 2021 Cochrane review is the careful answer. On pregnancy, treatment "may improve pregnancy rates compared to delayed or no treatment", a relative risk of 1.55 (confidence interval 1.06 to 2.26), which the authors rate low certainty: couples with no treatment had about a 21% chance of pregnancy, and treated couples somewhere between 22% and 48%. On live births, the honest summary is that "we are uncertain whether surgical or radiological treatment improves live birth rates", because the trials were too few and too small to tell.

Guidelines land in the same place. NICE says to consider radiological or surgical treatment for a varicocele found on examination, in men who are trying to conceive naturally and have reduced semen parameters. The EAU recommends treating men with a clinical varicocele, abnormal semen and otherwise unexplained infertility, and recommends against treating a varicocele that only a scan can find, or one in a man with a normal semen analysis. WHO's 2025 guideline suggests surgical repair over watchful waiting for men with a varicocele and abnormal semen parameters, as a conditional recommendation on very low-certainty evidence. If a doctor can feel it and your semen analysis is abnormal, it is a real option worth discussing; if it turned up only on an ultrasound, it is not.

Supplements: what the trials actually show

The 2022 Cochrane review of antioxidants pooled 90 randomized trials and more than 10,000 men. It found antioxidants may raise live birth rates (odds ratio 1.43, confidence interval 1.07 to 1.91) but graded that very low certainty, and the effect stopped being statistically significant once trials at high risk of bias were excluded (odds ratio 1.22, confidence interval 0.85 to 1.75). Clinical pregnancy showed a clearer signal at low certainty. Stomach upset was about 2.7 times more common on antioxidants than on placebo.

Worth noticing how that conclusion has moved: the 2019 version of the same review reported a larger live-birth effect and still called the evidence inconclusive, and the estimate has shrunk as more trials have been added. NICE advises against offering supplements or antioxidants to improve sperm DNA integrity, and the AUA tells clinicians to counsel patients that their benefit is "of questionable clinical utility". The supplements guide goes ingredient by ingredient.

What about the headlines saying counts have halved

They come from real papers. A 2017 meta-regression of 185 studies and 42,935 men reported a 52.4% fall in sperm concentration among Western men between 1973 and 2011, and a 2023 update covering 223 studies and 57,168 men put the worldwide fall at 51.6% between 1973 and 2018, with the yearly rate of decline roughly doubling after 2000, from 1.16% a year to 2.64%.

They are also contested by researchers in the same field. A 2022 review in Nature Reviews Urology concluded that the available data "do not enable us to conclude that human semen quality is deteriorating worldwide or in the Western world", pointing to changes in laboratory methods and in who gets tested across five decades. A separate 2021 analysis made the point that matters most here, that declining sperm counts do not predict declining fertility, because the relationship between a population average and any individual couple's chance is not proportional. Useful context for a national debate. Not information about you.

When to see a doctor

NICE NG257, published in March 2026, replaced the 2013 guideline. It advises assessment after a year of unprotected sex without conception, and referral straight away if the partner trying to conceive is 36 or over, or if either partner has a known or suspected cause of infertility or a history that predisposes to it. The NHS gives the same rule of thumb: a year, or six months if your partner is 36 or over.

On the test itself:

• An abnormal first analysis gets a repeat confirmatory test.
• The repeat comes ideally three months later, so it measures sperm made since the first.
• If the first test found no sperm or very few, the repeat happens as soon as possible rather than in three months.
• After two abnormal analyses, NICE advises an examination of the scrotum and testes, and considering testosterone and gonadotrophin blood tests.

The retesting guide covers the timing, and the UK sperm test guide covers the NHS route, clinic prices and home kits.

Two tests NICE says to skip

Worth knowing before a clinic offers them. NICE NG257 says "do not carry out testing for sperm DNA integrity (fragmentation)", on the grounds that the link with subfertility is not established and there is no agreement on which test or threshold to use. It also says not to offer supplements, antioxidants or medical treatments to improve DNA fragmentation. European guidance differs on the testing question in specific situations such as recurrent miscarriage, so it is a fair thing to ask a specialist about, but in the UK it is not part of a standard work-up and you should not be paying for it as one. The DNA fragmentation guide covers what the test shows and where the guidelines differ.

How long a change takes to show

Sperm take roughly two to two and a half months to make. Heller and Clermont's 1963 tracer study put the process at about 64 days; their 1964 paper revised it to about 74 days, which became the textbook figure. In 2006 Misell and colleagues had 11 men drink heavy water for three weeks and tracked the label into their sperm: it appeared after an average of 64 days, with a range of 42 to 76 days, covering the passage through the epididymis as well. The commonly repeated 90 days is a rounding, not a measurement.

That is the whole reason NICE puts three months between tests, and why the 74-day timeline tool gives you the first date a retest can reflect a change you start today. The how-long guide covers which changes show fastest.

Can you still conceive with a low count

Often, yes, and the honest framing is about odds rather than about a yes or no. Lower counts are linked to a lower chance each month and a longer time to conceive; except in azoospermia, they are not a statement that conception cannot happen. NICE's own baseline is that over 80% of couples conceive within a year when the woman is under 40, and about half of the rest conceive during the second year. Regular sex every two to three days is what NICE says optimizes the chance.

If treatment is needed, the options run from IUI through IVF to ICSI, where a single sperm is injected into an egg. The HFEA lists a very low sperm count, poorly shaped or poorly moving sperm, and sperm collected surgically as the usual reasons to use ICSI. For azoospermia, NICE offers surgical sperm retrieval and says to consider micro-TESE, except where a Y chromosome AZFa or AZFb deletion has been found, since retrieval does not succeed in that case.

What to do

• Treat one low result as a prompt to retest, not as an answer. Ask for the repeat about three months out, or straight away if very few sperm were found.
• Ask for your total sperm number and total motile count, not just concentration. They say more together than any one line does.
• Stop any testosterone or anabolic steroids, and tell the doctor you are taking them. Expect months, not weeks.
• Stop smoking, and work toward a healthy weight if you carry extra. These two have the most evidence of anything you control.
• Keep alcohol within 14 units a week spread across several days, and keep heat off the testes.
• Ask your GP to examine you for a varicocele. A palpable one with an abnormal semen analysis is worth discussing; one found only on a scan is not.
• Ask before paying for a DNA fragmentation test or an antioxidant protocol. NICE advises against both as routine.
• Have sex every two to three days rather than saving up for the right day.

Common questions

Related guides

• Every factor ranked
• Reading a semen analysis
• Improving motility
• Testosterone and fertility
• When to retest
• Male infertility statistics

Sources

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Correction, 8 October 2026. A sentence on finasteride gave figures without a source. It now points to the testosterone guide, which cites the studies.