The shampoo sitting beside the bathroom mirror, the plastic lunch box in the kitchen, the scented lotion rubbed onto the skin every morning and even traces of chemicals drifting through drinking water may be combining inside pregnant women in ways scientists are only beginning to understand. A disturbing new study from Spain has raised fresh concerns that this invisible "chemical soup" could interfere with the placenta—the unborn baby’s life support system—and may influence birthweight.

The research, published in the journal Environmental Science & Technology and led by scientists at Barcelona Institute for Global Health (ISGlobal), examined how mixtures of everyday environmental chemicals may affect pregnancy rather than studying one substance at a time. Researchers say the study reflects real life more accurately because people are constantly exposed to dozens of chemicals simultaneously through food, air, water and household products.

“Pregnant women are exposed to complex mixtures of chemicals rather than single compounds,” said Bethany Knox, ISGlobal researcher and first author of the study. “Our goal was to better reflect real-world exposures and understand how these mixtures might influence both the placenta and foetal development.”

The study followed 734 pregnant women in Barcelona between 2018 and 2021 under the Barcelona Life Study Cohort (BiSC). Scientists analysed more than 40 chemicals by studying urine samples collected over an entire week during two stages of pregnancy — at 18 weeks and 34 weeks. Inside the laboratory, researchers tracked chemical metabolites linked to phthalates, parabens, pesticides, phenols, and newer compounds, such as bisphenol S (BPS), a chemical increasingly used as a replacement for BPA in plastics.

The results indicated a disturbing trend. Mixtures containing low-molecular-weight phthalates – chemicals that are commonly found in perfumes, shampoos, plastic packaging, vinyl flooring and cosmetics – were consistently linked to lower birthweights in babies.

For doctors, birthweight is not just a number jotted down after delivery. Babies born with abnormally low weights can be at higher risk of infections, breathing problems, developmental delays and chronic illnesses later in life.

But what most concerned scientists was the way these chemicals appeared to work. During pregnancy, tiny blood vessels need to form correctly to allow the placenta to transfer oxygen and nutrients from mother to baby. The study found signs of disruption of those processes in some chemical mixtures.

Researchers observed changes in what are called angiogenic biomarkers — substances that regulate blood vessel formation in the placenta. In plain language, the chemicals appeared to disturb the placenta’s ability to build and maintain healthy blood flow to the developing baby.

The study specifically highlighted changes in the balance between two markers known as PlGF and sFlt-1. Scientists often monitor these markers because abnormal levels can indicate stress in placental function. When this balance shifts, the placenta may struggle to nourish the foetus effectively.

In another intriguing twist, mixtures containing organophosphate compounds, including some pesticides and flame retardants, were linked to higher birthweight. Researchers cautioned that the result may not necessarily mean the chemicals themselves are beneficial. Instead, they suspect the findings could reflect healthier diets rich in fruits and vegetables, which may unintentionally increase pesticide exposure while also supporting foetal growth.

Martine Vrijheid, coordinator of the study and head of ISGlobal’s Environment and Health over the Lifecourse Program, said the findings add to growing international evidence that environmental exposures during pregnancy deserve far greater attention from public health authorities.

Scientists across Europe and the United States have increasingly warned that endocrine disrupting chemicals—often called EDCs—can interfere with hormones that guide human growth, fertility, and metabolism. Earlier studies from institutions including Harvard T.H. Chan School of Public Health and National Institute of Environmental Health Sciences have also linked prenatal chemical exposure with developmental and reproductive concerns.

The ISGlobal researchers stressed that the findings should not create panic among individual mothers because the study examined population-level patterns rather than predicting outcomes for specific pregnancies. Yet the message remains difficult to ignore: the modern home itself may now be a source of constant low-level chemical exposure during one of the most delicate stages of human life.