Tardiness hair in transitional zone: Analysis between age and frontal forehead hairline in children aged below 5 years old

Objective: This study aimed to investigate the morphological characteristics and distribution of frontal hairline patterns among Chinese infants and young children aged 0–5 years and to explore the correlation between age and hairline morphology. Methods: A cross-sectional study was conducted on 213 infants and young children aged 0–5 years in the Dermatology Department of the Third Hospital of Peking University between February 2017 and February 2023. Participants are divided into four types based on the angle formed between the line connecting the point at the frontotemporal angle of the hairline and the tragus and the coronal plane[greater than 30 degrees (Type I), 15–30 degrees (Type II), 0–15 degrees (Type III), and less than 0 degrees (Type IV)]. The presence of temporal peak and skin color phototypes were also recorded. Ordinal logistic regression and restricted cubic splines were used to analyze the relationship between age and hairline phenotype. Results: Among the 213 participants, Type II (40.8%) and Type III (39.4%) hairlines were the most prevalent, while Type I (6.6%) was the least common. Multivariate regression analysis revealed a negative correlation between age and hairline type, which persisted after adjusting for potential confounding factors such as gender, temporal bulge, and skin phototype. Restricted cubic spline analysis further revealed a non-linear, inverse J-shaped relationship between age and hairline type. Conclusion: In infants and young children aged 0–5 years old, Type II and Type III frontal hairline patterns were most relevant. A negative correlation between age and hairline type were observed in this population.