BackgroundPer- and polyfluoroalkyl substances (PFAS) are ubiquitous chemicals routinely detected in personal care products (PCPs). However, few studies have evaluated the impact of PCP use on PFAS concentrations in pregnant and lactating populations. ObjectiveWe investigated associations between PCP use and PFAS concentrations in prenatal plasma and human milk. MethodsWe leveraged the Maternal-Infant Research on Environmental Chemicals (MIREC) Study to evaluate the contribution of PCP use on PFAS concentrations in prenatal plasma (6–13 weeks’ gestation; n = 1,940) and human-milk (2–10 weeks’ postpartum; n = 664). Participants reported frequency of use across 8 PCP categories during the 1st and 3rd trimesters, 1–2 days postpartum, and 2–10 weeks’ postpartum. We used linear regression models to quantify covariate-adjusted percent differences and corresponding 95 % confidence intervals. ResultsIn 1st trimester pregnant people, we found higher use of nailcare products (≥once a week vs never: perfluorooctanoic acid (PFOA): 21 % [9.7 %, 32 %]; perfluorooctane-sulfonic acid (PFOS): 11 % [0.3 %, 23 %]), fragrances (daily vs never: PFOA: 14 % [7.8 %, 21 %]; PFOS: 7.8 % [1.3 %, 15 %]), makeup (daily vs. never: PFOA: 14 % [5.8 %, 23 %]), hair dyes (never vs. > twice during pregnancy: PFOA: 8.3 % [2.4 %, 15 %]), and hair sprays or gels (daily vs. never: PFOA: 12 % [5.0 %, 19 %], PFOS: 7.1 % [0.2 %, 15 %], PFHxS: 9.9 % [0.6 %, 20 %]) were associated with higher plasma PFAS concentrations. Similar results were observed for 3rd trimester PCP use and 2–10 weeks’ postpartum human-milk PFAS concentrations. In addition, we found that people using colored-permanent dye 1 to 2 days postpartum had higher Sm-PFOS (18 % [ 2.7, 35]), PFOA (16 % [4.3 %, 29 %]), and perfluorononanoic acid (17 % [3.6 %, 33 %]) postpartum human-milk concentrations. ConclusionsOur results show that PCP use may be a modifiable source of PFAS exposure in pregnant and lactating populations. These results along with growing scientific evidence can help inform PFAS regulation and guide individual choices to reduce PFAS exposure.