A young man using an asthma inhaler
Second and Third-Born Children Show Lower Asthma Risk – Surprising Study Reveals
In Brief
- • A Taiwan study found that second- and third-born children have significantly lower risks of asthma and allergies than firstborns.
- • Researchers believe the difference may stem from greater early microbial exposure experienced by later-born children.
- • The findings suggest that declining birth rates and smaller families could contribute to rising allergy prevalence.
A new study has uncovered a surprising truth. Being a second or third-born child may actually protect you from asthma and allergies, and the reason has nothing to do with genetics. Researchers found a key environmental factor that might explain why firstborns face higher risks.
A report by a local news outlet in Taiwan where the study was carried out said the researchers set out to investigate why firstborns have higher chances of asthma and other allergies.
The discovery challenges common beliefs and highlights a possible environmental factor linked to early-life exposure. Researchers set out to understand why firstborns tend to show higher rates of asthma, eczema, and hay fever. While the team couldn’t pinpoint a single clear cause, they found a strong correlation with microbial exposure. Later-born children are exposed to more bacteria early in life through older siblings, potentially strengthening their immune systems.
Asthma Trends Highlight a Growing Concern
The birthrate in Taiwan has dropped from 3.69 in 1970, to 1.5 in 1998 and 0.87 in 2023, while the prevalence of asthma in children has risen from 1.3 percent in 1974 to 20.3 percent in 2019.
As a result, the researchers set out to investigate the causes of prevalence among children of different birth positions.
They found that higher birth order was associated with lower allergic disease risk. Second-born and third-or-later born children had reduced risks of asthma, eczema, and hay fever.
Researchers examined how birth order might influence this trend, discovering that higher birth order correlates with lower allergic disease risk. Second-born and third-or-later children experienced fewer cases of asthma. This strengthens the theory that smaller family sizes, now increasingly common worldwide, may unintentionally contribute to rising allergy prevalence.

What Other Studies Reveal About Allergies
While birth order appears to play a significant role, researchers caution that it’s only one part of a much broader picture. Allergies are becoming more common globally, and scientists are exploring multiple avenues to understand why.
One recent study reveals that most allergies can be quickly stopped by using a specific safe wavelength of ultraviolet light. But with global birth rates trending downward, the Taiwan study highlights an urgent need for continued research into how modern lifestyles may be shaping our immune systems.
As families get smaller and allergies continue to rise, understanding these environmental influences could be key to reversing the trend, and protecting future generations.
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