A 14-month-old infant presents with intense itching and visible erythema on both cheeks and forehead for the past 3 weeks. On examination, you note bilateral cheek erythema with scaling, but notably, the area marked **B** (central face including periorbital and nasolabial regions) is spared. The mother reports a family history of asthma. Which of the following best explains the characteristic sparing pattern seen at **B** in infantile atopic dermatitis?