What if a chemical we encounter almost every day could shape our health before we are even born? A new study suggests this may be happening through bisphenol A (BPA), a common chemical used in plastic food packaging.
The study, titled Developmental low-dose bisphenol A exposure leads to extensive transcriptome female masculinization and male feminization later in life, published in Communications Medicine, found that even very low exposure to BPA during pregnancy can cause long-lasting changes in the body. In rats exposed before birth, females later showed gene activity patterns typical of males, while males showed patterns usually seen in females.
These changes were linked to higher disease risk later in life. Females showed signs of shifting towards a cancer-like biological state, while males showed changes linked to metabolic syndrome, which raises the risk of diabetes and
heart disease.
What is bisphenol A (BPA)?
Bisphenol A is a synthetic chemical used to make certain plastics and resins. It is commonly found in food and beverage packaging, including some plastic containers and can linings. BPA is known as an endocrine disruptor, meaning it can interfere with hormones such as oestrogen, thyroid hormones, and androgens.
Why exposure during pregnancy may have lifelong consequences
The researchers stressed that the foetal stage is a period of intense biological programming. During this time, organs, immune systems and metabolic pathways are being set up for life. BPA can cross the placenta, meaning a developing fetus can be exposed through the mother.
In this study, pregnant rats were given drinking water containing BPA at two doses: one matching typical
daily human exposure, and another that was considered “safe” until 2015. After birth, the offspring were no longer exposed. Yet when they reached adulthood, nearly a year later, the effects were still clearly visible in their biology.
What does ‘feminisation’ and ‘masculinisation’ mean in this context?
The study said this is not about physical appearance or behaviour. The researchers examined gene activity, essentially which genes were switched on or off in the bone marrow, a key tissue for metabolism and immunity.
They found that BPA blurred the usual biological differences between sexes. Females exposed to BPA showed gene expression patterns closer to unexposed males, while exposed males shifted towards female-like patterns. In simple terms, BPA reduced the natural molecular distinctions between males and females.
According to the study, in females, the changes pointed towards a hypometabolic, cancer-like state, supported by signs of inflammation and altered blood markers. In males, the shifts suggested a hypermetabolic state resembling metabolic syndrome, which increases the risk of diabetes and cardiovascular disease.
The researchers also compared these findings with human data and found overlaps between BPA-induced changes in rats and metabolic patterns seen in people with metabolic syndrome, strengthening the relevance of the results.
The study also found that in males exposed to BPA, activity of T cells, which are key immune cells, increased, suggesting a heightened or dysregulated immune response. In females, T cell activity decreased.
This matters because immune imbalance is linked to chronic inflammation, autoimmunity and cancer risk. The study adds weight to earlier evidence that BPA disrupts immune regulation in subtle but lasting ways.
How BPA exposure may be linked to PCOS risk
According to the study, in female rats, BPA exposure led to reduced glucose levels, higher insulin levels, and signs of increased testosterone activity. This hormonal and metabolic pattern closely resembles polycystic ovary syndrome (PCOS).
Previous human studies have shown that women with PCOS tend to have higher BPA levels in their blood. The new data provide biological clues that help explain how BPA exposure could contribute to hormone imbalance and reduced fertility.
Why even tiny amounts of BPA worry scientists
Researchers said the damage occurred even at low doses that many people are likely to be exposed to every day.
This challenges the long-held belief that harm only increases as exposure rises. Instead, the findings add to growing evidence that hormone-disrupting chemicals like BPA can be especially powerful at very low levels, particularly when exposure happens early in life.
The researchers said that while this study was conducted in animals, the biological mechanisms uncovered are relevant to humans and add urgency to calls for stricter regulation of BPA in food packaging.
 "How a common plastic chemical may feminise males, masculinise females")
