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Fever, Flu, COVID, and Sperm: Can Being Sick Temporarily Affect Male Fertility?

A significant fever can temporarily worsen sperm count, motility, morphology, and DNA integrity. That does not mean permanent infertility — and it can explain a surprising semen analysis weeks later.

Updated September 29, 2026•11 min read•Primary-source grounded
Quick answer

High fever can temporarily affect sperm production because developing sperm are temperature-sensitive. Studies have documented semen changes appearing weeks after febrile illness and recovering over the following months. A recent fever is important context for a semen analysis, not a reason to assume permanent infertility.

Where are you right now?

The timeline matters because sperm develop over months

Planning aheadNo need to delay TTC because you once had a cold. Focus on recovering normally.
Trying nowA high fever may temporarily lower semen quality, but couples do not automatically need to stop trying.
Abnormal semen testTell the clinician about significant fever or acute illness in the prior roughly three months before interpreting the result as baseline.

Why fever can affect sperm after the illness is over

Sperm production takes place over a long developmental cycle. Heat-sensitive germ cells can be affected during a febrile illness, and the semen changes may not be obvious until the affected cells reach later stages.

That is why a man can feel completely recovered while the semen analysis several weeks later looks worse than expected.

What studies have found

Small prospective and case-report studies have documented temporary declines in sperm concentration, motility, morphology, and DNA-integrity measures after significant febrile illness.

In one detailed case, count and several sperm-quality markers worsened after a high fever and substantially recovered over subsequent weeks to months. Another study following men longitudinally found that fever timing during spermatogenesis was associated with lower sperm concentration and worse motility or morphology.

The evidence is not precise enough to predict what a particular flu, COVID case, or other infection will do to one person's fertility.

Is it the virus or the fever?

Both can matter, depending on the infection. This article is specifically about the well-described thermal effect of significant fever on spermatogenesis.

Some infections can also affect reproductive tissues, inflammation, sexual function, or overall health independently of temperature.

Should you stop trying for three months after a fever?

Not as a universal rule.

A transient reduction in semen parameters is not the same as a known genetic or fetal risk from conception after fever. Couples may reasonably continue trying unless a clinician gives a specific reason not to.

The stronger practical implication is for testing: if a semen analysis is unexpectedly poor shortly after a significant fever, repeat testing after recovery may be more informative than treating one result as permanent.

What counts as “significant fever”?

Research showing substantial sperm effects generally involves genuine febrile illness rather than a temperature of 99°F for an evening.

Duration and height of fever appear to matter, but there is no consumer-friendly threshold that perfectly predicts sperm impact.

What if you are scheduled for IUI or IVF?

Tell the fertility clinic about recent high fever before sperm collection or treatment. Depending on timing, baseline semen history, available frozen samples, and the treatment plan, the information may affect counseling or whether repeat testing is useful.

The reassuring part: Heat-related semen impairment from acute fever is usually discussed as temporary. A low result after illness should be interpreted with the illness timeline attached.

Frequently asked questions

Can the flu lower sperm count?

A significant febrile illness can temporarily reduce sperm concentration and other semen parameters, regardless of which infection caused the fever.

How long can fever affect sperm?

Changes can appear weeks later and may recover over the following months because sperm development is a long process.

Should a semen analysis be repeated after fever?

If the result is abnormal and significant fever occurred in the preceding months, repeat testing after recovery may help distinguish a transient change from a persistent issue.

Sources & guidance

Medical disclaimer: This is educational information, not individualized medical advice. Do not stop prescribed medication, delay needed treatment, or make pregnancy-timing decisions solely from a consumer article. Review your specific medical history, medications, exposures, and pregnancy plans with qualified healthcare professionals.