For how we live.
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.
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.
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.
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.
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.