Taiwan study finds later-born children less likely to develop allergies

台灣研究發現，越晚出生的孩子罹患過敏的幾率越低

TAIPEI (Taiwan News) — A Taiwanese study indicates that a child’s position in the birth order may affect their likelihood of developing allergic diseases, CNA reported Wednesday.

The research found that children born later in the family tend to have a lower risk of asthma, allergic rhinitis, and atopic dermatitis. Third-born children, for example, showed a 26.9% lower risk of asthma compared with first-borns.

The study was led by Chan Chin-kan (詹金淦), an attending pediatrician at Taoyuan Hospital’s Department of Pediatrics. Chen Pau-chung (陳保中), director of the National Institute of Environmental Health Sciences and attending physician at National Taiwan University Hospital, served as a corresponding author.

Taiwan has seen a significant decline in fertility over the past decades, with the total fertility rate falling from 3.69 in 1970 to 0.87 in 2023. However, childhood allergic diseases have increased over the same period.

The prevalence of atopic dermatitis rose from 1.4% in 1974 to 11.3% in 2019. Asthma increased from 1.3% to 20.3%, and allergic rhinitis grew from 7.8% to 50.6%.

The study analyzed the country’s birth registration data from 2004 to 2014 and linked it with the Taiwan Birth Registration Database to examine the relationship between birth order, fertility rates, and allergy prevalence. The results showed that, regardless of gender, maternal age, or socioeconomic status, being born later in the family was associated with a lower risk of allergic diseases.

Further analysis revealed that second-born and third-born children, including those born third or later, had significantly lower risks compared to first-born children.

The risk of atopic dermatitis decreased by 21.3% for second-borns and 37.5% for third-borns or later. Asthma risk fell by 25% and 26.9%, respectively, while allergic rhinitis was 16.3% lower for second-borns and 29.3% lower for third-borns or later.

The study also identified a clear negative correlation between national fertility rates and allergy prevalence. The research team suggested that declining fertility rates and smaller family sizes may contribute to the increasing prevalence of childhood allergies, likely due to reduced early-life microbial exposure.