Which statement best describes formalin pigment formation and its prevention?

• A. It forms under acidic formalin conditions; keeping fixative pH above 6.0 helps prevent it
• B. It forms under basic conditions; lowering pH prevents it
• C. It forms only during dehydration; dehydration conditions prevent it
• D. It forms during embedding; selecting paraffin prevents it

Answer: (A)

Formalin pigment is an artifact that forms when tissue is fixed in acidic formalin. In acidic conditions, formaldehyde reacts with tissue components (especially sulfur-containing residues) to produce a dark brown‑black pigment that can deposit in cells and mimic other pigments. Keeping the fixative at a neutral to slightly alkaline pH, typically above 6.0, prevents this chemical environment from occurring, so the pigment does not form. This phenomenon is linked to the fixation step, not dehydration or embedding, which is why correcting the fixative pH is the effective preventive measure.