The same Parkinson's patient has crusty and erythematous labial commissures. What is the most likely cause?

Correct answer: A. Candida

• A. Correct. Angular cheilitis (perlèche) at the commissures is most commonly caused by Candida albicans, often with a co-infecting Staphylococcus; saliva pooling in the folds (common with ill-fitting dentures/drooling) promotes it.
• B. Vitamin C deficiency causes scurvy (gingival bleeding), not the classic commissure cracking — riboflavin/B-vitamin or iron deficiency is more associated with angular cheilitis.
• C. HSV produces grouped vesicles on the lip vermilion (herpes labialis), not crusting confined to the commissures.
• D. Actinic cheilitis affects the lower lip from chronic sun exposure, not the angles of the mouth.