My baby also have 粒粒 on face when she was near 3 weeks old. I brought her to see doctor immediately law. He said it may due to allergy caused by new milk power or new pillow wow. He game me some cream. 粒粒 disappeared after several times of application of cream.
No need to see doctor but you must clean BB's face several times. My BB also 生晒粒粒 when he was 2 weeks, then I clean his face with warm water. Now his face is so smoothy.