Phthalates, which are endocrine-disrupting chemicals (EDCs), are mainly used in plastic products as plasticizers, making them elastic and pliable. Humans are exposed to phthalates from a wide range of sources through inhalation, digestion, or dermal absorption (1, 2), including diet, unique hygiene products, cosmetics and skin products, medical applications, and recreational and pharmaceutical agents (2–5). Experimental and observational studies have suggested that phthalates can negatively affect male and female reproductive health via interference with estrogen/androgen production and/or inflammatory/oxidative stress pathways (6–11).

Prenatal, postnatal, and childhood exposure to phthalates affects hormone levels and pubertal development; however, the underlying mechanisms remain unclear (1, 12–15). Eales et al. (14) summarized the high-to-moderate health effects of phthalates and their metabolites, which include lower semen quality, impaired neurodevelopment, risk of childhood asthma, anogenital distance in boys, low birth weight, endometriosis, decreased testosterone levels, type 2 diabetes, and breast/uterine cancer. Basso et al. (15) considered that phthalates and their metabolites are crucial environmental factors contributing to the etiology of uterine and ovarian diseases in women, such as polycystic ovary syndrome and endometriosis.

Phthalates induce various cellular responses, including the modulation of the expression of steroid hormone receptors and transcription and paracrine factors. For example, male rats treated with di(2-ethylhexyl)phthalate (DEHP) exhibited delayed puberty and changes in serum anti-Mullerian hormone (AMH), estrogen levels, follicle-stimulating hormone (FSH), and gene expression (16). The research findings indicate that exposure to DEHP in animal experiments is linked to reduced gene expression and expression of critical proteins. This exposure may contribute to the development of defects, such as abnormal uterine structure, epithelial proliferation, uterine receptivity, and endometrial shedding in rats (17, 18). These results highlight the potential adverse effects of DEHP exposure on reproductive health and provide insight into the mechanisms by which DEHP affects the reproductive system. Further studies are needed to investigate the long-term effects of DEHP exposure and its impact on human health.

The age of puberty onset varies widely among individuals across ethnicities and sexes (6–10, 19). Puberty begins between the ages of 8 and 12 years in girls and 9 and 14 years in boys (20–22). The exact mechanism that triggers puberty onset remains elusive (20–24). Kisspeptins belonging to the neuropeptide family may be associated with female puberty initiation and ovulation regulation through the central control of the hypothalamus–pituitary–gonad axis. Increased prenatal or early childhood exposure to phthalates positively correlates with elevated kisspeptin concentrations, suggesting that such exposure may accelerate sexual maturation in girls (22, 25–27). Although epidemiological studies have limitations, they suggest that phthalates may affect reproductive outcomes and children’s health.

The human development cycle is classified into infants, toddlers, preschool- and school-aged children, adolescents, and young adults, before reaching adulthood (28). Our previous studies on phthalate metabolites have indicated that the phthalate exposure concentration might affect sex steroid hormone levels and negatively affect uterus development in girls (7, 8). Most cohort epidemiological studies have focused on the effects of gestational exposure to maternal or neonatal hormones on childhood puberty development or adulthood reproductive health; however, sensitivity to phthalate exposure is not limited to the fetal and neonatal periods. In this study, we examined the association between prenatal to childhood phthalate exposure (prenatally and at 2, 5, 8, and 11 years old) and the development of puberty and reproductive organs in 14-year-old children.

This study conducted a 15-year follow-up of the effect of prenatal and childhood exposure to phthalates on pubertal development in a population-based birth cohort. Initially, a total of 445 children were recruited from 2000 to 2001. Twenty-one children were excluded who were not born in our hospital, 166 children who had never attended follow-up since birth, seven children whose birth dates were unknown, and 31 children without a maternal urine test data. Among the 220 eligible children, a total of 90 completed all three surveys at 8, 11, and 14 years of age during the follow-up period, while the remaining 130 children did not provide complete responses. Thus, the overall response rate for the study was 40.9% (90/220). Figure 1 illustrates a flowchart describing the details of the study population.

This study was approved by the Ethics Review Committee of the National Health Research Institutes in Taiwan, and informed written consent was obtained before the commencement of the study from each of the pregnant participants, the guardian, and the children ≥6 years of age using suitable language for children’s understanding.

In the present follow-up study, we examined the association between the pubertal and reproductive development of 14-year-old male and female children and prenatal and environmental exposure to phthalates. Some urinary phthalate metabolite levels correlated with developmental stages in all children. Regarding the development of reproductive organs, we observed evidence of an association between phthalate exposure and reduced utero size.

According to the survey data of the Ministry of Health and Welfare between 2017 and 2020, 14-year-old boys in Taiwan had an average height of 167.7 cm, weight of 62.8 kg, and BMI of 22.2 kg/m², while girls had an average height of 159.6 cm, weight of 53 kg, and BMI of 20.7 kg/m² (33). Our study found that the average height of boys and girls were within the normal growth curve; however, girls who exhibited adult characteristics showed a tendency towards being overweight. During puberty, the levels of GH and IGF-1 increase significantly, leading to a rapid increase in bone and muscle growth (34–36). This growth spurt is further amplified by the increased production of sex steroids, particularly estradiol in females and testosterone in males (34–36). In girls undergoing normal puberty, it is common to observe a physiological increase in body mass index (BMI) and subcutaneous adiposity (37). This phenomenon is likely attributable to the hormonal changes that occur during puberty, including increases in estrogen and other hormones that promote the accumulation of adipose tissue (36–38). In addition, physical activity and participation in sports during adolescence tend to decline, especially among teenage girls (38). This finding does not provide sufficient evidence to infer a causal relationship between height, obesity, and puberty development.

Early puberty can be categorized based on the degree of early onset, which includes premature thelarche (early breast development), premature adrenarche (early pubic hair development), and true precocious puberty (36). Current research indicates that phthalates are associated differently with breast and pubic hair development (36, 39–43). The evidence indicated that MEP is related to early onset of breast development (12, 44), while DEHP and its metabolites may be related to delayed pubic hair development (39–41). Our study results revealed that the MEHP and MEHHP levels of 11-year-old girls were negatively correlated with the Tanner stage at 14 years of age, and the MEP level at 2 years old was associated with a higher Tanner stage at 14 years of age. However, these results cannot establish causality for pubertal delay. The impact of phthalate exposure on pubertal development in girls may have both positive and negative effects.

Animal experiments have demonstrated that exposure to phthalate metabolites before and after birth can lead to decreased TT production, alterations in male reproductive development and function, and delayed puberty (40, 42, 43). However, the available epidemiological data are limited and inconsistent (41, 45–48). A prospective cohort study conducted in Russia has revealed that significantly higher prepubertal urinary concentrations of phthalate metabolites were associated with later pubarche. Specifically, higher concentrations of MiBP, MBzP, and ΣDiNP were associated with a delay in gonadarche (49). In our study, some boys with Tanner stage < 4 exhibited a negative correlation with MBzP exposure at 11 years old, and no correlation was noted between the testicular volume and phthalates. However, at 11 years old, exposure to DEHP, MEHP, MEHHP, and MBzP was negatively associated with testosterone at 14 years of age ( Supplementary Table S3 ), similar to the results of Burns et al. (49). Based on these results, in the future, we will consider exploring the association between phthalate exposure during hormone-sensitive pre-and peri-pubertal stages and pubertal development timing among males.

For boys, maternal phthalate exposure probably has adverse effects on the male fetus, with an increased risk of urogenital developmental abnormalities (11). In an early study, marmoset monkeys were treated daily with 0, 100, 500, or 2500 mg/kg DEHP by oral gavage for 65 weeks from weaning (3 months of age) to sexual maturity (18 months) (50). Even in monkeys treated with 2500 mg/kg DEHP throughout the preadolescent period, no histological changes were noted in the testes (50). However, recent animal and human studies have indicated that phthalate exposure results in adverse seminiferous cord effects (51–54), including changes in seminiferous cord development, Sertoli cell function, germ cell death, and multinucleation of germ cells (51, 52).

A meta-analysis concluded that a positive association exists between phthalate exposure and pubertal timing (12). A Swedish cohort study reported that young men (aged 17–20 years) with the highest prenatal levels of the diisononyl phthalate (DiNP) metabolite had a lower testicular volume, and that DEHP was significantly associated with a lower semen volume (54). A cross-sectional Danish study did not find any association between phthalate exposure, testicular growth, and measurable testosterone levels (48). A Spanish study surveyed the association between phthalates and pubertal development in children aged 7–10 years, and the results revealed that child obesity modifies the association of prenatal phthalate exposure with puberty (21).

Some phthalates can disrupt estrogen signaling, increasing estrogen levels, and possibly causing uterine disorders (55, 56). Our previous study detected a significant association between reduced uterine size and increased exposure to MEHP and total DEHP among 11-year-old girls (8); the results also revealed that the uterine size at 14 years of age was negatively related to MEHP, MnBP, MMP, and MBP levels at 8 years and the MBzP level at 14 years of age. For female marmoset monkeys, increased ovarian and uterine weights and elevated blood estradiol levels were observed in higher dosage groups (500 and 2500 mg/kg) (50). However, these increased uterine weights were associated with a large corpus luteum, a common finding in older female marmosets (50). The uterus is a crucial target organ in mammalian development in terms of sexual maturation, and uterine cells respond to estrogen and progesterone for the regulation of endometrial cell proliferation and differentiation (15). Exposure to DEHP can alter the number of endometrial glands and disrupt their structure in rats and mice (17, 18, 56).

Our data also indicated a positive or negative correlation between the hormonal levels of 14-year-old girls and exposure to some phthalates at specific time points ( Supplementary Tables S3–S8 ). Furthermore, an association was noted between phthalate exposure at the age of 14 years and hormonal performance in girls. The association between sex hormone levels at 14 years of age and phthalate exposure was the most obvious at the ages of 8 and 11 years, respectively. Another critical window is puberty because the targets of endocrine glands usually show a higher sensitivity to hormones during a specific developmental stage (26, 57). Future studies must investigate the correlation between sex hormones and the uterus. Phthalates are typically stored in adipose tissues. The adipose tissue in girls tends to increase and be redistributed during puberty (22, 26). During this period, girls have a higher likelihood of phthalate accumulation in the adipose tissue; however, this relationship requires further research.

There are limitations to this study. First, the approximately 80% sample size loss to follow-up in this birth cohort study may have caused bias in the exposure–outcome association estimates. A temporal relationship or causality could not be inferred between phthalate exposure and the children’s reproductive developmental indices. Furthermore, EDCs widely exist in human lives; this study lacks an analysis of the effects of co-exposure to EDCs. In the future, animal models or human epidemiological studies with careful exposure assessment will be necessary to determine the causal relationship between individual phthalate exposure and its effects on development. These studies should include adequate sample sizes, standardized exposure protocols, and longitudinal assessments to capture the potential cumulative effects of phthalate exposure over time.

In conclusion, exposure to phthalates at certain time points may be associated with reproductive organ development in girls. Determining whether exposure to phthalates affects later reproductive function requires further investigation. Although we observed that exposure to phthalates at a specific time might be associated with subsequent sexual organ or hormonal effects, this assumption arose from an epidemiological study design. These hypotheses should be proven by randomized studies employing relevant animal models or using a more rigorous epidemiology study design.

The original contributions presented in the study are included in the article/ Supplementary Material . Further inquiries can be directed to the corresponding authors.

This study was approved by the Ethics Review Committee of the National Health Research Institutes in Taiwan, and informed written consent was obtained before the commencement of the study from each of the pregnant participants, the guardian, and the children ≥ 6 years of age using suitable language for children’s understanding. Written informed consent to participate in this study was provided by the participants’ legal guardian/next of kin.

Conceptualization: P-HS. Formal analysis: J-YH. Funding acquisition: None. Methodology: P-HS, S-LW. Writing–original draft: H-PC. Writing–review and editing: P-HS and H-PC. All authors contributed to the article and approved the submitted version.