A mother is concerned about what might have caused a heat rash on her infant. The nurse observes tiny pinhead-sized reddened papules on the infant's neck and axilla. What does the nurse explain as the most likely cause of this rash?

A. Sun exposure: Sun exposure typically causes sunburn rather than tiny pinhead-sized papules. B. Allergic reaction: Allergic reactions often present with different types of lesions or hives, not typically tiny papules. C. Infection: Infections might cause different types of lesions or pustules rather than the described tiny papules. D. Heat and moisture: Heat rash (miliaria) results from blocked sweat ducts, leading to tiny red papules due to overheating and trapped sweat, commonly occurring in areas like the neck and axilla.