Are sperm counts and testosterone really falling? Experts weigh the evidence
September 27, 2026 · 17 min read
Epidemiologist Shanna Swan points to endocrine-disrupting chemicals and microplastics as drivers of a global fertility decline. Urologist Michael Eisenberg takes a more cautious look at whether testosterone is truly declining and what else, like obesity, explains it. Knowing where the evidence is strong and where it is contested helps readers act without panic.
The rules, numbers and steps worth keeping in front of you.
- Swan: the 50% drop in sperm count over 50 years survived every confounder she modeled.
- Eisenberg: the sperm data are disputed; the testosterone decline is more convincing.
- Eisenberg: obesity explains about a 10% decline out of a reported 50%.
- Swan: below about 40 to 45 million sperm per milliliter, the chance of conception drops steeply.
- Swan: exposure in the womb cannot be reversed; an adult smoker can quit and recover.
- Swan: fragrance is a major phthalate source; if you can smell it, it is probably affecting your hormones.
- Swan: never put plastic in a microwave; replace non-stick pans with iron.
- Swan: labels saying BPA free often hide similar chemicals.
- Huberman: one serving of canned soup a day for five days raised urinary BPA more than a thousand percent.
- Huberman: microplastic findings in humans are correlations, not proof of cause.
- Huberman: sperm take about 90 days to reflect a change; avoid heat such as seat heaters.
- Eisenberg: you cannot judge testosterone or sperm quality by appearance; test.
- Eisenberg: about 15% of men have low semen quality, often without knowing.
- Fertility concerns or low testosterone symptoms: see a urologist or reproductive specialist.
This is the short form. The full insight has every expert's reasoning, their own words and the sources.