Skepticism doubts all proofs without regard for the fact that all proof, all skepticism is itself based upon the existence of proofs and the lack thereof.

There are several bases for skepticism, and many social and philosophical movements that call themselves some form of skeptic.  The Scientific Skeptics seem to have little more purpose than to debunk unscientific claims.  Philosophical Skeptics question the basis of all knowledge and Methodical Skeptics construct ways to evaluate claims.

One may be skeptical of everything including the existence of skepticism.  Rational belief places a reliance on the only universally valued concepts, those that are reasonable.  We can test what is reasonable by what works and conversely if it works it is reasonable.