To ensure the added hair looks natural, start by matching the color, texture, and lighting of the existing hair. Use Layer Blending Modes like Overlay or Soft Light to blend the new hair seamlessly with the original. Pay attention to highlights and shadows by using the Dodge and Burn tools to match the light source in the image. Adjusting opacity and using subtle gradients can also help the new hair integrate smoothly into the photo, creating a realistic effect.