The odds of fathering a child have simply become worse than they were a generation ago.
A lo largo de medio siglo, la capacidad reproductiva masculina en España ha experimentado un deterioro silencioso pero profundo: la concentración espermática ha caído un 66% desde 1973, y las infecciones de transmisión sexual, los disruptores endocrinos y los hábitos de vida modernos siguen erosionando lo que queda. La reciente estabilización de los datos ofrece un respiro técnico, pero no una solución; en un país donde la maternidad se pospone cada vez más, la biología masculina y la demografía convergen en un desafío que apenas comienza a nombrarse.
- La concentración espermática media en España ha caído a 33,5 millones por mililitro, un 66% menos que en 1973, y el volumen del eyaculado se ha reducido un 17% en solo cinco años.
- Las infecciones de transmisión sexual detectadas en muestras de semen pasaron del 32% en 2019 al 42% en 2024, mientras que la morfología normal de los espermatozoides se ha desplomado del 7% a apenas el 3%.
- Pesticidas, disruptores endocrinos, estrés crónico, tabaco y sedentarismo forman un entorno que presiona silenciosamente sobre la fertilidad masculina sin que exista aún una respuesta preventiva coordinada.
- La estabilización reciente de los parámetros seminales es un alivio frágil: los especialistas advierten que los valores actuales ya representan una amenaza real para la fertilidad poblacional en España.
- La demanda de técnicas de reproducción asistida crece, pero los expertos reclaman un giro hacia la prevención: regulación ambiental, campañas de salud pública y una cultura que tome la salud reproductiva masculina tan en serio como la femenina.
Los hombres españoles producen hoy espermatozoides significativamente menos viables que hace cincuenta años. La concentración espermática media se sitúa en 33,5 millones por mililitro, frente a los 99 millones registrados en 1973, y el ritmo de caída se aceleró entre 2011 y 2026, cuando la concentración bajó otro 28% en apenas quince años. El fenómeno no es exclusivo de España: a nivel global, la concentración espermática ha caído un 51% desde 1973, con una tasa de deterioro que se duplicó a partir del año 2000. La OMS respondió revisando a la baja sus propios estándares de semen saludable, un reconocimiento implícito de que el punto de partida ha cambiado para toda la especie.
Más allá de la concentración, otros indicadores empeoran. El volumen del eyaculado ha caído un 17% en cinco años, y la morfología normal de los espermatozoides ha pasado del 7% a apenas el 3% en menos de una década, según el análisis de más de 8.000 muestras realizado por el Instituto Bernabeu. A esto se suma un aumento preocupante de las infecciones de transmisión sexual en las muestras: del 32% en 2019 al 42% en 2024. Los especialistas señalan un conjunto de factores: contaminantes ambientales, disruptores endocrinos, tabaco, drogas, estrés crónico, sedentarismo y ciertos medicamentos.
La única señal moderadamente alentadora es que el descenso parece haberse detenido. Los datos más recientes del Instituto Bernabeu muestran que concentración, motilidad y morfología se mantienen estables respecto a mediciones de hace dos años. Pero los especialistas advierten que estabilizarse en niveles tan bajos no equivale a recuperarse, y que la tendencia a retrasar la maternidad hasta los treinta o cuarenta años estrecha aún más la ventana para la concepción natural.
Las consecuencias se extienden al sistema sanitario y demográfico: la infertilidad masculina impulsa una demanda creciente de reproducción asistida, y las clínicas atienden cada vez más parejas que necesitan intervención para concebir. Los expertos reclaman medidas preventivas —regulación ambiental más estricta, campañas de salud pública, diagnóstico precoz de infecciones— y un cambio cultural que otorgue a la salud reproductiva masculina la misma atención que históricamente se ha dedicado a la femenina. Esa conversación, por ahora, apenas está comenzando.
Spanish men are producing less viable sperm than they did fifty years ago, and the recent leveling off of that decline offers little comfort to fertility specialists watching the numbers. The average sperm concentration among Spanish males now sits at 33.5 million per milliliter—a figure that represents a 66 percent drop from the 99 million per milliliter recorded in 1973. Even more alarming, the decline accelerated sharply in recent decades: between 2011 and 2026, concentration fell another 28 percent in just fifteen years, from 47.1 million to today's depressed baseline.
This is not a Spanish problem alone. Globally, sperm concentration has fallen 51 percent since 1973, with the rate of decline doubling since the year 2000. The World Health Organization responded by revising its standards for what constitutes healthy semen downward—a tacit acknowledgment that the baseline itself has shifted. A man now needs more than 16 million sperm per milliliter and adequate progressive motility to be considered in the optimal range under the WHO's 2021 manual. But as Dr. Eva María García of Instituto Bernabeu explains, the practical consequence is stark: the odds of fathering a child have simply become worse than they were a generation ago.
Beyond raw concentration, other markers of semen quality are deteriorating. Instituto Bernabeu, analyzing more than 8,000 semen samples, found that ejaculate volume has dropped 17 percent in just the past five years. This matters because total motile sperm count—the number of sperm actually capable of swimming toward an egg—depends partly on volume. Morphology, the shape and structure of individual sperm cells, has also worsened: only 3 percent of sperm per sample now appear structurally normal, compared to 7 percent less than a decade ago. These are not marginal shifts. They represent a biological trajectory that, if it continues, will reshape fertility across the population.
Sexually transmitted infections are compounding the problem. The percentage of semen samples showing signs of STI infection jumped from 32 percent in 2019 to 42 percent in 2024—a ten-point increase in five years. Specialists point to a constellation of culprits: environmental contaminants like pesticides and endocrine-disrupting chemicals; lifestyle factors including tobacco and drug use; chronic stress and physical inactivity; certain medications; and undiagnosed infections that silently damage reproductive tissue. Some researchers hypothesize that prolonged exposure to portable electronic devices, which generate heat near the testicles, may also impair sperm production, though human evidence remains inconclusive.
The one piece of potentially good news is that the downward spiral appears to have paused. Instituto Bernabeu's most recent data show sperm concentration, motility, and morphology holding steady at levels similar to measurements taken two years earlier. No dramatic improvement, but no further deterioration either. Yet specialists are careful not to overstate what stabilization means. Dr. Ana Fabregat of Instituto Bernabeu warns that even at current levels, these values pose a genuine threat to fertility in the Spanish population. The challenge now is not just to stop the decline but to reverse it—and to do so while more and more Spanish women delay motherhood into their thirties and forties, a demographic trend that compounds male fertility problems by narrowing the window for natural conception.
The implications ripple outward. Male infertility now accounts for a growing share of reproductive difficulties in Spain, driving increased demand for assisted reproduction techniques. Clinics are seeing more couples who need intervention to conceive. Specialists are increasingly turning to sperm cryopreservation—freezing sperm while quality is still adequate—for men with severely diminished semen parameters. But these are reactive measures. Experts are calling for a shift toward prevention: better environmental regulation, public health campaigns about lifestyle and reproductive health, earlier diagnosis of infections and other treatable conditions, and a cultural reorientation that treats male reproductive health with the same seriousness long afforded to female fertility. For now, that conversation is only beginning.
Citas Notables
The probability of achieving pregnancy depends on semen parameters. A man with adequate sperm concentration and progressive motility is considered optimal under WHO 2021 standards, but the decline in recent decades means the odds of fatherhood are not what they were years ago.— Dr. Eva María García, Instituto Bernabeu
These values, if they continue at current levels, could pose a threat to fertility in our population. The challenge is identifying factors that allow us to improve semen quality and act preventively, including sperm freezing for men with severely diminished quality.— Dr. Ana Fabregat, Instituto Bernabeu
La Conversación del Hearth Otra perspectiva de la historia
Why does it matter that sperm concentration has stabilized if it's stabilized at such a low level?
Because stabilization without improvement is a trap. It means we've stopped getting worse, but we're not getting better. The damage is already done—men today have half the sperm their grandfathers did. Stabilization just means we're not digging the hole any deeper.
What's driving the decline? Is it one thing or many things?
It's many things working together. Environmental toxins, stress, sedentary life, infections that go untreated. We can point to pesticides and chemicals that disrupt hormones. We can point to smoking and drug use. But no single culprit explains it all. That's what makes it so hard to fix.
The STI numbers jumped from 32 to 42 percent in five years. That's a huge shift. Why?
That's the part that worries specialists most because it's partly preventable. STIs damage reproductive tissue, and they're rising. Whether that's because more men have them, or because more men are being tested and diagnosed, we can't say for certain. But the trend is real.
If a man's sperm quality is very poor, what can he actually do?
Right now, the main option is cryopreservation—freezing sperm while it's still viable, before it deteriorates further. But that's a stopgap. The real answer would be prevention: treating infections early, changing lifestyle, reducing environmental exposure. Those things take time and coordination across society.
How does this connect to women delaying motherhood?
It's a collision of two trends. Women are having children later because of education, careers, economics. But male fertility is declining. So you have fewer viable sperm meeting eggs at an age when female fertility is also declining. The window for natural conception gets narrower for everyone.
What would actually reverse this?
That's the question no one has a clear answer to yet. You'd need to identify and remove or reduce whatever's causing the decline—environmental contaminants, lifestyle factors, infections. You'd need prevention at a population level, not just treatment at the clinic. And you'd need to start talking about male reproductive health the way we talk about female reproductive health. Right now, that conversation barely exists.