This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Alopecia, Subject name: Skin
'Exclamation mark' hair is a feature of - 
Select and explain. 
A. Telogen effluvium, B. Androgenetic alopecia, C. Alopecia areata, D. Alopecia mucinosa
C: Alopecia areata
Answer: C: Alopecia areata 
Explanation: Ans. is 'c' i.e., Alopecia areata Exclamation mark is a feature of Alopecia Areata.Alopecia areata manifests as completely asymptomatic localized areas of alopecia from which all or most of the hairs have been lost.The key to the diagnosis of Alopecia areata isNo itchingNo scalingNo scarringDue to these features it can be easily distinguished from other diseases which cause localized areas of alopecia.Presence of Exclamation mark hairs '7/i nearly a third of the patients, the hair shaft develops a node of trichorrhexis 5-70 mm from the root at which the hair breaks off leaving behind a small fragment of each of these hairs in the patch. Such hair are called exclamation mark hairs".