In fact, the formal writing should be "Yan". In Shuowen Jiezi, there is Yan without Yan, Yan Naihou is a secular word, and Yan is not a surname. Today, the so-called Yan surname appears because the second Chinese character simplification scheme (which was later abolished) mistakenly simplified the traditional Chinese characters of Yan surname into characters. So Yan Zhengzi should be Yan.

Yan surname is another branch of Yan surname. According to the surname spectrum, there are two surnames, Yan and Yan. According to "Five Tones with Same Rhyme", Yan is "the same, sharing". Because Yan and Yan are of the same ancestry, they are both descendants of the Yellow Emperor and the dragon, so Yan and Yan's family names are Taiyuan, and their aristocratic families lived in Taiyuan County in ancient times (it is said that Yan's aristocratic family lived in Tianshui). Because Yan's "vulgarity" entered Yan, there were two surnames, Yan and Yan, so among the hundreds of surnames, the two surnames coexisted.