If you're huffing on your camera lens and smearing it with your shirt, you're doing it all wrong.
There's actually nothing wrong with breathing on your lens.
The problem comes when you clean it.
When you use a T-shirt to wipe your lens clean, anything but 100% cotton can create micro-scratches and streaks, that only make your lens grimier.
The fact is that, you're probably cleaning your lens more than you should.
Little specks of dust won't effect your photos, so resist the urge to clean until it's absolutely necessary.
When you need to clean your lens, do this.
First, use a microfiber cloth, lens tissue, or lens pen to wipe away any dust or smudges.
If that doesn't help, add a drop of two of lens Lens cleaning solution to the cloth.
And if you're really dying to get rid of dust, use a blower brush.
Not your mouth and now you're doing it right.