Cancer　still　threats　human　health　rigorously.　Most　current　options　of　photosensitizers　(PSs)　are　plagued　with　“always　on”,　accounting　for　limited　signal-to-noise　ratio　in　the　lesions　and　undesired　side　effects　in　normal　tissues.　Inspired　by　the　redox　imbalance　of　tumor　microenvironment,　redox-activated　PSs　(RA-PSs)　are　coming　to　frontiers　that　enhance　diagnosis　accuracy　and　treatment　efficiency.　Herein,　the　progress　of　PSs-based　therapy　is　outlined.　Furthermore,　the　design　strategies　of　RA-PSs　are　discussed,　including　potential　mechanism　and　linkage　to　obtain　on-demand　switchable　optical　signals.　Moreover,　versatile　RA-PSs　for　real-time　visualization　and　therapy　are　highlighted.　Finally,　future　prospects　and　challenges　are　spotlighted.　©　2024　Elsevier　B.V.