How to blur a face in Photoshop?

Final Image

Step – 1. Open your photo you like to blur in photoshop. Go to Tool Bar > Marquee Tool > Chose Rectangular Marquee Tool and select on face you like to blur.

Step – 2. Go to Menu Bar > Filter > Pixelate >  Mosaic. 

Step – 3. In the Mosaic box, you can change the Cell Size How much you want to use.

Done! If you have any question, please feel free to ask.