**Core Concept**
Breast milk contains various bioactive compounds that provide protection against infections and diseases in infants. These compounds play a crucial role in the development of the infant's immune system and gut microbiota.

**Why the Correct Answer is Right**
The protective effects of breast milk are primarily attributed to the presence of immunoglobulins, particularly IgA, which forms a critical barrier against pathogens in the gut. Additionally, breast milk contains oligosaccharides that serve as prebiotics, promoting the growth of beneficial bacteria in the infant's gut, thereby supporting the development of a healthy gut microbiota. This symbiotic relationship between the infant's gut and the beneficial bacteria helps to prevent infections and supports the maturation of the infant's immune system.

**Why Each Wrong Option is Incorrect**
**Option A:** While breast milk does contain some amounts of cortisol, this hormone is not primarily responsible for the protective effects of breast milk.

**Option B:** Although breast milk does contain some amounts of thyroxine, this hormone is not directly responsible for the protective effects of breast milk.

**Option C:** While breast milk does contain some amounts of growth hormone, this hormone is not primarily responsible for the protective effects of breast milk.

**Clinical Pearl / High-Yield Fact**
The World Health Organization recommends exclusive breastfeeding for the first six months of life, as it provides optimal nutrition and protection against infections and diseases.

**Correct Answer:** C.