What a semen analysis can and cannot tell a man about his fertility
It anchors every male-infertility evaluation, but its reference numbers come from a few thousand fertile men — and a normal result never rules fertility in or out.
Testosterone therapy suppresses sperm — the opposite of a fertility boost
Exogenous testosterone switches off the body's own signals to the testes. In a male-contraceptive trial, 95.9 per 100 men fell to near-zero sperm counts. The effect is usually, but not always, reversible.
At-home sperm tests count how many, not how well they swim or look
Consumer kits reliably estimate sperm concentration, and a smartphone assay matched lab classification ~98% of the time. But a normal count can't rule out the motility, shape and DNA problems a full analysis checks.
PFAS and semen quality: small associations, and only for two measures
A meta-analysis of 14 studies and 7,465 men found little for the conventional semen parameters, and something more consistent for sperm DNA fragmentation.
Boxers are linked to 25% higher sperm concentration. No study links them to babies.
The scrotal-cooling theory is sound and the semen findings are real. A 2026 review found the prospective data show no difference in pregnancy outcomes by underwear type.
Obesity and sleep disorders track with worse semen. Alcohol mostly does not.
An umbrella review graded 249 effect sizes across 67 risk factors for male infertility. More than half were rated very low certainty — and the review contradicts its own table on one of them.
The sperm count decline is real in one dataset and unproven in another
A 223-study meta-regression reports sperm concentration falling 51.6% since 1973. Two published critiques argue the method cannot support that reading. Both sides are peer-reviewed.