Previous studies identified various mechanisms of light scattering reduction in tissue induced by chemical agents. Our results suggest that dehydration is an important mechanism of optical clearing in collagenous and cellular tissue. Photographic and optical coherence tomography images indicate that air-immersed skin and tendon specimens become similarly transparent to glycerol-immersed specimens. Transmission electron microscopy images reveal that dehydration causes individual scattering particles such as collagen fibrils and organelles to become more densely packed, but does not significantly alter size. A heuristic particle-interaction model predicts that the scattering particle volume fraction increase can contribute substantially to optical clearing in collagenous and cellular tissue.