PetaPixel pointed out a Nikon support thread that specifically says not to use your breath:
Do not breathe on the lens to fog it for cleaning. There are harmful acids in breath that can damage lens coatings.
Uh oh. Then what the hell are we non-professional photographers supposed to do? Nikon says lens cleaning solutions are the best (no abrasives, no solvents) but if you don’t have that, use “the blower bulb, then brush, and wipe the lens in a circular spiral from the centre outward.” The more you know, right. [Nikon via PetaPixel]