Researchers have found two-month-old babies with larger thymuses face a sixfold higher risk of atopic dermatitis by the time they turn two.
Infants with a larger thymus size at two months of age are significantly more likely to develop atopic dermatitis within the first two years of life, a new longitudinal study has revealed.
The research, published in Allergy – The European Journal of Allergy and Clinical Immunology, followed 300 term newborns from birth through their second birthday, examining the role of early T-cell maturation in the development of AD.
“Our findings indicate that increased thymic activity and T-cell development may be associated with a higher risk of AD onset, suggesting a potential role of early-life T-cell maturation in disease pathogenesis,” the authors concluded.
The study sought to explore the connection between thymic development – key organ in T-cell maturation – and immune dysregulation associated with AD, a common chronic inflammatory skin disease in early childhood.
Using trans-sternal ultrasound scans, researchers measured thymus size at birth, two months and 12 months, calculating the thymic index and focusing particularly on those in the top 10th percentile for size.
Skin tape strip samples from the dorsal hand were also analysed for immune biomarkers to assess local immune activation.
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Out of the 300 children enrolled, 290 were included in the final analysis. The two-year cumulative prevalence of AD was 34.1%, and those with a higher thymic index at two months of age had a notably higher risk of developing AD.
The adjusted hazard ratio for AD during the first two years of life was 6.32, indicating more than a sixfold increased risk compared to those with smaller thymuses.
A similar trend was observed for early-onset AD diagnosed before six months of age, with an adjusted hazard ratio of 5.35.
A moderate correlation between thymic index and eczema severity, measured by the Eczema Area and Severity Index (EASI), was observed at two months of age.
The study suggested that increased thymic activity could serve as a biomarker for identifying infants at high risk for AD, with possible implications for early surveillance and preventive strategies in paediatric populations.
While the findings did not establish a direct causal link, they opened the door to further investigation into how early immune architecture shaped susceptibility to allergic disease.
The authors advocated for additional studies to explore the mechanisms behind these associations and to evaluate whether early immunomodulatory interventions might alter the disease trajectory.
Allergy – The European Journal of Allergy and Clinical Immunology, July 2025
