
Birth Order May Tilt Your Risk for ADHD, Allergies, and More
New research analyzing health data from over five million two-child families finds birth order is linked to different disease risks: first-borns have higher odds of neurodevelopmental conditions (ADHD and autism) and of food allergies and hay fever, while second-borns show higher odds of substance-use disorders and gastrointestinal conditions. A shorter gap between siblings may offer some protective effect for certain neuropsychiatric and allergic conditions. Experts caution these are population-level associations rather than causal links, and birth order is a non-modifiable, relatively weak predictor of individual risk.













