Hair Dyes in Pregnancy: A Systematic Review and Meta-Analysis.

OBJECTIVE

The main objective is to investigate the association between periconceptional or pregnancy exposure to hair dyes and obstetric and pediatric outcomes.

METHODS

A systematic literature search was conducted in Scopus, PubMed/MEDLINE, Web of Science, and CINAHL Ultimate from database inception to August 31, 2024. Studies were included based on PECO criteria: pregnant women and their newborns (population), exposure to hair dyes during periconception or pregnancy (exposure), no exposure (comparator), and any obstetric or pediatric complication (outcome). After screening 311 records and removing duplicates, 179 abstracts were reviewed, 29 full texts assessed, and 20 observational studies included. Four reviewers assessed bias and extracted data. Meta-analyses were performed using a random-effects model when appropriate.

RESULTS

Few studies distinguished hair dye types or exposure timing. Periconceptional or pregnancy hair dye exposure was reported to be associated with stillbirth, low birth weight (Pooled OR 2.30; 95% CI 1.24-4.25), and low hormone levels; in the offspring, with allergic rhinitis, leukemia, neuroblastoma (pooled OR 1.79; 95% CI 1.20-2.68), Wilms tumor (pooled OR 6.00; 95% CI 1.22-29.46), germ cell tumors, and membranous ventricular septal defect. No association was observed with asthma (pooled OR 1.19; 95% CI 0.86-1.65), childhood brain tumors (pooled OR 1.06; 95% CI 0.88-1.28), or mental retardation. Based on the GRADE assessment, the certainty of evidence was low or very low.

CONCLUSIONS

Current observational evidence suggests a potential association between periconceptional or pregnancy exposure to hair dyes and some adverse obstetric and pediatric outcomes. However, given the low and very low certainty of evidence and the retrospective nature of most included studies, these findings are hypothesis-generating and preclude causal inference. Further prospective studies are needed to confirm these preliminary associations and define the specific chemicals involved.