Stains & CD markers
Oil red O

Editorial Board Member: Raul S. Gonzalez, M.D.
Editor-in-Chief: Debra L. Zynger, M.D.
Chunyu Cai, M.D., Ph.D.

Last author update: 24 August 2020
Last staff update: 17 June 2021

Copyright: 2003-2024,, Inc.

PubMed Search: Oil red O [title]

Chunyu Cai, M.D., Ph.D.
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Cite this page: Cai C. Oil red O. website. Accessed February 26th, 2024.
Definition / general
  • Oil red O is a fat soluble, hydrophobic diazo dye that stains neutral fat, fatty acids and triglycerides (Histochemistry 1992;97:493)
    • Maximum absorption at 518 nm; appears red under light microscopy
  • Unlike Sudan black, oil red O stains poorly for complex phospholipids and glycolipids that have polar groups, meaning it does not stain myelin / peripheral nerve or biological membranes
  • In order to highlight fat droplets, oil red O staining needs to be performed on fresh or frozen tissue; paraffin embedding or alcohol based fixation removes most neutral lipids
Essential features
  • IUPAC name: 1-(2,5-dimethyl-4-(2,5-dimethylphenyl) phenyldiazenyl) azonapthalen-2-ol
  • Chemical formula: C26H24N4O
  • Red cytoplasmic / sarcoplasmic stain in muscle biopsy
  • In fat emboli, red staining fat globules in the lumen of capillaries
Uses by pathologists
Frozen section images

Contributed by Robert E. Schmidt, M.D., Ph.D.
Fat embolism brain

Fat embolism brain

Fat embolism kidney

Fat embolism kidney

Microscopic (histologic) images

Contributed by Chunyu "Hunter" Cai, M.D., Ph.D.
Normal muscle

Normal muscle

Carnitine deficiency

Carnitine deficiency



Positive staining - normal
Positive staining - disease
Sample pathology report
  • Right quadriceps, biopsy:
    • Lipid storage myopathy (see comment)
    • Comment: The morphologic features of this biopsy are those of a lipid storage myopathy and include conspicuous vacuolar change, staining of the vacuoles in the oil red O stain and excess sarcoplasmic lipid vacuoles by ultrastructural examination. The cause of the lipid accumulation is not apparent in this biopsy. The differential diagnosis of adult onset lipid storage myopathy include primary and secondary carnitine deficiency, as well as a number of rarer entities including multiple acyl-CoA dehydrogenase deficiency, lipin 1 deficiency, neutral lipid storage disease with ichthyosis and neutral lipid storage disease with myopathy. Serum carnitine and acylcarnitine analyses, as well as urine organic acid analysis may be of additional diagnostic value. Cardiomyopathy and fatty liver disease should be ruled out by appropriate clinical means.
Board review style question #1
Which of the following special stains can be used to highlight both lipid droplets and myelin in muscle biopsies?

  1. Gomori trichrome
  2. Oil red O
  3. Sudan black
  4. Verhoeff van Gieson (VVG) stain
Board review style answer #1
C. Sudan black. Gomori trichrome can stain myelin red but does not stain lipid. Oil red O stains lipid red but does not stain myelin. VVG stains elastin and myelin but not lipid.

Comment Here

Reference: Oil red O
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