Masson's Trichrome Stain

Classic collagen fiber stain, which distinguishes collagen fibers from muscle fibers.

In the strict sense, connective tissue comprises three types of fibers: collagen, reticular, and elastic. Collagen fibers are the most abundant and widely distributed. Masson's trichrome stain, also known as the Masson stain, is the classic method for staining connective tissue and represents the authoritative technique for visualizing collagen fibers. Trichrome staining typically targets cell nuclei while selectively differentiating collagen from muscle fibers. The staining principle relies on the molecular size of anionic dyes and their ability to penetrate tissue. Smaller molecules penetrate dense, low-permeability tissues more easily, whereas larger molecules only access loose, highly permeable structures. Since green light or aniline blue have large molecular weights, they bind to collagen rather than muscle; consequently, after Masson staining, muscle fibers appear red, while collagen stains green (with green light) or blue (with aniline blue). This method is primarily used to distinguish collagen fibers from muscle fibers.