Little black dots and balding on the neck

Hi there,

I trimmed some of the hair on the neck of my persian cat because they got knotted a couple weeks ago. Today I just noticed that a part on the neck is hairless and the skin has little dark dots on it.

I am not sure if that area is hairless because of trimming but I just trimmed down the hair, now it looks more like its shaved with almost no hair.

Here is a photo of the area and the dots. He has the same dots (but much less) near his nipples. Does anyone have any idea about the dots?