Bouin fixative is used for which stain?

• A. Masson Trichrome
• B. Aldehyde fuchsin
• C. Oil Red O
• D. Phosphotungstic acid-hematoxylin

Answer: (A)

Bouin fixative is especially good at preserving and highlighting collagen fibers, which is exactly what Masson Trichrome is designed to differentiate. In this trichrome staining sequence, nuclei are usually stained dark, muscle/cytoplasm takes on a red hue, and collagen is colored blue by the aniline blue component. The picric acid in Bouin’s fixative helps preserve and reveal the delicate collagen fibrils so they bind strongly to the blue dye, producing a clear contrast between connective tissue and muscle. This makes Bouin-fixed tissue yield sharp, interpretable connective tissue patterns and fibrosis with Masson Trichrome. The other stains target different tissue components—elastic fibers, lipids, or muscle/platelets—and don’t rely on Bouin’s fixation to achieve their characteristic differentiation, which is why they aren’t typically associated with Bouin fixative.