A new study published on March 25, 2026 by researchers at the University of Oxford has found that sperm quality declines significantly during periods of sexual abstinence, and that ejaculating more frequently may actually improve the health of sperm in men. The findings, which analysed data from nearly 55,000 men across 115 published studies, challenge the widely held medical advice that men should abstain from ejaculation for several days before fertility tests or assisted reproduction procedures.

The research was conducted by Rebecca Dean, a Research Fellow in the Department of Biology at Oxford, alongside Irem Sepil, a Lecturer in Evolutionary Biology, and Krish Sanghvi, a PhD Candidate in Biology. The study’s findings have significant implications for fertility treatment, reproductive health advice, and our understanding of how male biology ages differently from female biology.

How Male Sperm Storage Works

To understand why the findings matter, it helps to understand how male reproduction differs from female reproduction. Women are born with most of their lifetime supply of eggs, meaning a woman’s age and the age of her eggs are effectively the same. Male reproduction works differently. Sperm are produced continuously from puberty onwards and can be stored in the male reproductive tract before ejaculation. This means a man’s age is not necessarily the same as the age of his sperm at the time of fertilisation.

The question the Oxford researchers set out to answer was: what happens to sperm while they wait in storage? The answer, their data suggests, is that stored sperm ages and deteriorates in ways that meaningfully affect fertility outcomes.

What the Study Found

Analysing semen data from 115 published studies involving nearly 55,000 men, the researchers found that when men abstained from ejaculation, the health of their sperm dropped significantly across multiple measures. Sperm motility, which is the ability of sperm to swim effectively toward an egg, decreased during abstinence. Sperm viability, meaning the proportion of sperm that are alive and functional, also declined. And perhaps most significantly, sperm DNA became more damaged during periods of storage.

The researchers identified two primary biological mechanisms driving this deterioration. The first is oxidative stress, described in the study as a form of biological rust that accumulates in stored sperm and causes physical damage over time. The second is energy depletion. Unlike most cells in the human body, sperm are highly active cells that have only a limited capacity to replenish their energy reserves. When stored for extended periods without ejaculation, sperm essentially run out of the fuel they need to function properly.

The Challenge to Standard Medical Advice

The findings directly challenge guidance from the World Health Organisation, which currently advises against ejaculating for two to seven days before providing a sperm sample for analysis, fertility treatments, or procedures such as IVF. The rationale behind this recommendation has been that abstinence increases sperm count and therefore improves the chances of successful fertilisation.

The Oxford study suggests that while abstinence does increase sperm count, the quality of those sperm may actually be lower than freshly produced sperm due to the deterioration that occurs during storage. The researchers note that their findings support a recent clinical discovery that ejaculating within 48 hours of providing a sperm sample for IVF improves treatment outcomes compared to longer durations of abstinence. In other words, for IVF success, sperm freshness may matter more than sperm quantity.

The Evolutionary Biology Angle

The study also provides an evolutionary perspective on male masturbation that has rarely been explored in mainstream research. The researchers note that in primates, frequent ejaculation from masturbation has been observed to improve the quality of ejaculates. Combined with their findings in humans, this leads the researchers to propose that male masturbation may have an adaptive biological benefit: it flushes out damaged, aged sperm from the reproductive tract and replaces them with fresher, higher-quality sperm.

This hypothesis suggests that what has often been dismissed as having no reproductive function may in fact serve a meaningful biological purpose in maintaining sperm quality across periods when conception is not actively being attempted.

The Pattern Extends Across the Animal Kingdom

To test whether sperm deterioration during storage is a widespread biological phenomenon rather than specific to humans, the Oxford team examined data from 56 studies across 30 different animal species including birds, bees, reptiles, and other mammals. The pattern held consistently across species. In every group examined, sperm quality declined during storage periods.

The researchers found that fathers who stored sperm for longer before ejaculation, and mothers in species where females store sperm internally before fertilisation, produced embryos with lower chances of survival. This suggests the consequences of sperm deterioration extend beyond the sperm itself to affect embryo development and survival.

One particularly interesting finding was that sperm deteriorated at a slower rate when stored inside females than when stored inside males. The researchers suggest this is because females in several species have evolved specialised organs that secrete antioxidants which nourish and protect stored sperm, effectively extending their functional lifespan. This biological asymmetry points to an evolutionary adaptation in which female reproductive systems have developed mechanisms to preserve sperm quality that male reproductive systems have not independently developed.

What This Means for Men Trying to Conceive

The practical implications of the Oxford study are meaningful for couples attempting to conceive, particularly those undergoing fertility treatment. The researchers conclude that using freshly ejaculated sperm for fertilisation could provide a meaningful boost to fertility outcomes by improving sperm quality at the time of attempted conception.

For men undergoing IVF or other assisted reproduction procedures, discussing the timing of ejaculation before sample provision with their fertility specialist in light of these findings is a conversation worth having. The standard two to seven day abstinence window recommended by the WHO may warrant reconsideration in the context of this new evidence, though any changes to clinical protocols would need to be made in consultation with medical professionals on a case-by-case basis.

The Broader Context of Declining Fertility

The Oxford researchers note that their findings are particularly timely given two converging global trends. Sexual activity appears to be declining, especially among young people. And the global trend toward delayed parenthood means that more couples are attempting to conceive at older ages when both egg and sperm quality are naturally lower. The combination of these trends may compound global fertility declines in ways that are only beginning to be understood.

The finding that the duration of sperm storage is a modifiable factor in sperm quality is significant precisely because so many other contributors to fertility decline, including environmental toxins, chronic stress, and genetic factors, are outside an individual’s control. Sperm storage duration, by contrast, is something that can be actively managed, making it one of the few fertility variables that is directly actionable.

This article is based on research published on March 25, 2026 by Rebecca Dean, Irem Sepil, and Krish Sanghvi from the University of Oxford’s Department of Biology, published via The Conversation under Creative Commons licence. This article is for informational purposes only and does not constitute medical advice. Readers with fertility concerns are advised to consult a qualified medical professional.

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