As Hume said, skepticism may be self-refuting, but in the process of refuting itself it undermines dogmatism. Skepticism, Sextus said, is like a purge that eliminates itself as well as everything else. ... Hume, therefore, made a distinction between philosophical doubt and natural, practical human activities.

Can radical skepticism be refuted?

In short: this sort of radical skepticism cannot be refuted because it cannot be stated; the radical skeptic parasites on our epistemological discussions raising objections to any claim to knowledge, without stating any thesis of their own. That's the only reason why their skepticism holds.

How can skepticism be reduced?