this is 斑秃 (alopecia areata), most likely due to

来源: 于 2009-08-19 14:12:50 [博客] [旧帖] [给我悄悄话] 本文已被阅读：次
stress (just like 茶mm said: 可能是精神紧张等原因).

It will eventually grow back in most cases.