Blue bruising is a chemical reaction set off by damage. In Psilocybe cubensis, a 2020 study found that an enzyme called PsiP removes psilocybin’s phosphate to make psilocin, and a second enzyme, PsiL, oxidizes psilocin so that its units link into blue pairs and chains (Lenz et al., 2020). The same team wrote that “no single blue compound exists” in these mushrooms.
A 2021 follow-up corrected part of the picture: the main early blue product turned out to be a pair joined at a different position from the one first proposed (Lenz et al., 2021). Why the mushroom does this is unresolved; the leading idea is defence, and a 2024 genus study notes that the blue chains are tied to psilocybin-making even in lineages that gained it separately (Bradshaw et al., 2024).
The colour is no guide to strength. Psilocin is “gradually consumed” as the blue forms (Lenz et al., 2020), and a 2025 study wrote that bluing “does not necessarily correlate with psilocin levels” (Windsor et al., 2025). Other mushrooms turn blue through unrelated chemistry, so the colour is not a safe sign of what a mushroom is.
Sources
- Lenz et al., 2020, Angewandte Chemie: PsiP and PsiL
- Lenz et al., 2021, Chemistry – A European Journal: the blue products revisited
- Windsor et al., 2025, Journal of AOAC International: bluing and psilocin levels
- Bradshaw et al., 2024, PNAS: Psilocybe phylogenomics
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