Understanding Methylene Blue in Embalming
Methylene blue (MB) is a dark crystalline powder that turns blue when dissolved in water or alcohol. Originally synthesized in 1876 by Heinrich Caro as a textile dye, it was later found to stain certain bacteria, leading to its use in microbiology. By 1891, Paul Ehrlich successfully used MB to treat malaria, making it the first synthetic drug ever created. Today, it continues to be used in medicine, notably for treating methemoglobinemia—a condition that prevents hemoglobin from releasing oxygen. It has also been studied for its potential to enhance mitochondrial function and improve cognitive abilities. It is also popular for its antimicrobial characteristics, which was first noted by Ehrlich.
However, what does this mean for embalmers? The increased use of MB in medical treatments, particularly during the COVID-19 pandemic, has made it more relevant in postmortem care. Because MB is a highly pigmented dye, it can tint a decedent’s tissues blue or green. While living individuals metabolize MB into a colorless form within 24–48 hours, postmortem conditions can lead to a persistent discoloration due to its interaction with hemoglobin.
Methylene blue comes in two forms- the blue color and leucomethylene blue, which is white or clear. It changes color because of what is known as a redox reaction. Redox reactions are basically shifts in electrons allowing for a chemical to take on oxygen or not. What we need to know for this discussion is that when methylene blue is oxidized, it is blue (a mnemonic is “Babe the Blue Ox”) and when its reduced, it’s clear.
Why Does MB Cause Postmortem Discoloration?
- Interaction with Hemoglobin – MB can oxidize hemoglobin, creating methemoglobin, which has a distinct blue tint. This process has been known to continue postmortem in low-oxygen environments, leading to persistent staining.
- Oxidation During Autopsy – Studies have documented cases where MB-treated individuals developed blue-green discoloration upon exposure to atmospheric oxygen. This phenomenon has been nicknamed the "pistachio" or "avatar" effect.
- Post-Embalming Oxidation – Even if a decedent appears normal before embalming, MB’s colorless metabolite (leucomethylene blue) can oxidize back to blue when exposed to oxygenated blood during the process, resulting in unexpected discoloration.
The Role of Embalming Chemistry
It’s easy for us as embalmers to initially blame formaldehyde for the post-embalming color shift. However, a historical test from 1902—the Schardinger’s reaction—suggests otherwise. This test, which used MB to detect formaldehyde in unboiled milk, demonstrated that formaldehyde actually reduces MB to its colorless form rather than oxidizing it. Given that the enzyme responsible for this reaction, xanthine oxidase or the Schardinger enzyme, is present throughout the human body, the oxidation process in embalming is likely influenced by other factors. Formaldehyde is both an oxidizer and reducer, so it’s not completely ruled out, but it may be a low-level suspect in this case.
Potential oxidizing agents in embalming fluids were reviewed via Safety Data Sheets, but only a few were identified. Since this is very much in the hypothesis phase, it also wouldn’t be fair to call out those chemicals, because they are effective chemicals. One ubiquitous chemical I don’t mind naming as an oxidizer that could contribute is chlorine, which is commonly present in water used to dilute embalming chemicals. Reducing the water content in cases where MB treatment is known may help mitigate discoloration. Additionally, glutaraldehyde, frequently used in edema treatment, is a reducing agent and is unlikely to contribute to oxidation.
The Impact of pH on MB Discoloration
pH fluctuations also play a crucial role in oxidation-reduction (redox) reactions. In a well-documented experiment known as the "blue bottle experiment," MB changes color based on pH and oxygen exposure. Given the unpredictable postmortem pH shifts due to medical treatments and decomposition, MB could possibly undergo oxidation post-embalming, intensifying the blue hue.
