There are a few things you need to know if you want to add hair in Photoshop. First, make sure that your hair is properly aligned and placed in the image. Second, use a hair brush to create a light and evenly distributed coverage over your head. Finally, use a dark hair brush to create thicker or darker hair layers.
GROW HAIR on a BALD Head with Photoshop!
Check out How To Add Sparkles In Photoshop?