**Core Concept**
Breast milk contains a lower concentration of bilirubin-conjugating enzyme glucuronyl transferase compared to cow's milk. This enzyme is essential for the conjugation and subsequent excretion of bilirubin. As a result, breastfed infants may experience a higher bilirubin level, leading to jaundice.

**Why the Correct Answer is Right**
Jaundice in an exclusively breastfed baby is due to the immaturity of the liver enzyme glucuronyl transferase. This enzyme is responsible for converting unconjugated bilirubin into its water-soluble form, which can then be excreted in the bile. Breast milk contains a lower concentration of this enzyme, leading to an accumulation of unconjugated bilirubin in the blood. As a result, breastfed infants may develop jaundice, particularly in the first few days of life.

**Why Each Wrong Option is Incorrect**
**Option B:** Scurvy is caused by a deficiency of vitamin C, which is not typically a concern in breastfed infants unless the mother's diet is severely deficient. Breast milk contains adequate amounts of vitamin C to meet the infant's needs.
**Option C:** Tetany is usually associated with hypocalcemia or hypomagnesemia, which is not directly related to breast milk feeding. Breastfed infants may experience hypocalcemia due to maternal hypocalcemia or other underlying conditions, but this is not a direct consequence of exclusive breastfeeding.
**Option D:** Eczema can be associated with various factors, including allergies, environmental factors, and genetic predisposition. While breast milk can contain allergens that may contribute to eczema, this is not a direct consequence of exclusive breastfeeding.

**Clinical Pearl / High-Yield Fact**
In breastfed infants, jaundice can be a normal finding, particularly in the first few days of life. However, if jaundice persists beyond 7-10 days, it is essential to investigate underlying causes, such as biliary atresia or other liver disorders.

**✓ Correct Answer: A. Jaundice**