The cells, hormones and antibodies in breast milk help protect babies from illness. This protection is unique; formula cannot match the chemical makeup of human breast milk. In fact, amoung formula-fed babies, ear infections and diarrhea are more common. Formula-fed babies also have higher risks of gastrointestinal issues, lower-respiratory infections, asthma, obesity and Type 2 diabetes. Some research shows that breastfeeding can also reduce the risk of Type 1 diabetes and atopic dermatitis (a type of skin rash) in babies.
— Source: Office on Women’s Health, U.S. Department of Health and Human Services