This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Acne and chemical peeling, Subject name: Dental
Which is pathognomic lesion of acne vulgaris? 
Select and explain. 
A. Papules, B. Pustules, C. Comedones, D. Wheals
C: Comedones
Answer: C: Comedones 
Explanation: Comedones are pathognomic of acne. Comedones are the keratin plugs of the pilosebaceous ducts. When the keratin plug is inside the follicle, it is called closed comedone (whitehead). When the keratin plug is exposed to the environment, it turns black and is known as open comedone (blackhead). Comedonal lesions are the earliest lesions of acne. Typical acne lesions are comedones, inflammatory papules, pustules and nodules.