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December 1970

Formalin Pigment in Skin

Author Affiliations

Miami, Fla

From the Department of Dermatology, University of Miami School of Medicine, Miami, Fla.

Arch Dermatol. 1970;102(6):670-673. doi:10.1001/archderm.1970.04000120088017

Formalin pigment (acid formaldehyde hematin) is an iron-free derivative of hemoglobin that forms in skin when a specimen containing hemoglobin is fixed in acid formalin at pH less than 6. With low-power light microscopy, formalin pigment appears brown and granular and must be differentiated from melanin, hemosiderin, aposiderin, and hematoidin. Higher power reveals formalin pigment to be microcrystalline and birefringent. To avoid this artifact, tissue should be fixed in properly buffered formalin.