BACKGROUND
Thyroid hormone plays an important role in normal pregnancy and normal development of the baby. Abnormal thyroid hormone levels in mothers during pregnancy can lead to pregnancy complications and may affect baby’s development, especially brain development. Many personal care products used in skin care and cosmetics contain chemical ingredients such as phthalates, bisphenols, and per- and polyfluoroalkyl substance (PFAS), commonly referred as endocrinedisrupting chemicals (EDCs). These EDCs have been linked to abnormal thyroid function. Since personal care products are frequently used by women of childbearing age, exposure to these chemicals through personal care products may have negative effect on thyroid function in young women and in pregnancy.

Previous studies on potential impact of EDCs on thyroid function have limitations. Many previous studies looked at impact of several different hormones at the same time, which makes it harder to pick out impact on thyroid hormones. This study used data from 84 previous studies on the impact of EDCs as a base for more specific assessment of impact of EDCs from personal care products on thyroid function in pregnancy.

THE FULL ARTICLE TITLE
Sultan M,, et al. Association of exposure to personal care product chemicals with maternal thyroid health: a prospective cohort study integrated with targeted risk assessment for environmental chemicals strategy. Environ Int. 2026;208:110121; doi: 10.1016/j. envint.2026.110121. PMID: 41650877.

SUMMARY OF THE STUDY
Blood samples from 803 pregnant women in Nanjing, China, were analyzed. A total of 21 chemicals in personal care products were measured from blood samples collected in the second trimester, including two bisphenols, eight phthalates and their metabolites, and eleven PFASs. Thyroid hormone and thyroid antibody levels were measured from blood samples collected in the second and third trimesters. The researchers combined data from 84 previous studies (including studies in humans, animals, and at the cellular level) to assess a specific risk for abnormal thyroid function for each chemical.

The researchers also noted the quality of data from each study. Using this strategy, they generated a score indicating impact of all chemicals on thyroid function together, a score indicating impact of each class of chemicals on thyroid function, and a score indicating impact of each individual chemical on thyroid function. Scores were on 0–10 scale with score of 0–4.0 indicating low risk, score of 4.1–8.0 indicating medium risk, and score of 8.1–10.0 indicating high risk.

EDCs were detectible in 70–80% of blood samples of participants. All the chemicals scored as a medium risk. Medium risk chemicals are thought to have moderate risk to cause abnormal thyroid function and would require active monitoring and further research. For each class of EDCs, phthalates scored highest at 5.47, followed by PFASs at 4.85, and then bisphenols at 4.12. Several individual chemicals in all three categories showed significant associations with thyroid hormone levels, although they had variable effects on different measures of thyroid function tests: some chemicals were associated with low thyroid hormone levels while others were associated with high thyroid hormone levels. Exposure to higher amount of the mixture of all the chemicals was associated with lower level of TSH level in the second trimester, which may indicate elevated thyroid hormone levels, but it was not associated with changes in free T4 level or thyroid antibody levels.

WHAT ARE THE IMPLICATIONS OF THIS STUDY?
This study using a targeted score system derived from previous study data reported that exposure to EDCs contained in personal care products in pregnancy pose a medium risk of thyroid problems. The findings highlight need for further research regarding impact of EDCs exposure on pregnancy outcomes and potential need to decrease exposure to personal care products during the vulnerable periods of pregnancy when possible.

In their analyses, the researchers found that the evidence from human studies was the least reliable compared to cell or animal studies. This suggests that the evidence regarding potential impact of these EDCs on thyroid function in humans is still weak. Therefore, more data is needed to inform decisions for regulations and clinical guidelines. Further studies are also needed to evaluate potential impact of small changes in thyroid function seen in this study on adverse pregnancy outcomes and impact on baby’s development.

— Sun Lee, MD

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