Level 1: Why do babies have poor resistance? The baby\’s immunity has not yet fully matured and is easily affected by the external environment, resulting in weak resistance. In addition, if the baby is born with a low weight, or is born prematurely or underweight, its immune development will also be affected. Level 2: How to improve baby’s resistance? 1. Reasonable diet: Breast milk is the best food and can provide rich nutrients and immune substances.