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Chemistry

Walnut hulls contain diverse phytochemicals, such as polyphenols, that stain hands and can cause skin irritation. Seven phenolic compounds, including ferulic acid, vanillic acid, coumaric acid, syringic acid, myricetin, and juglone, were identified in walnut husks; juglone had concentrations of 2-4% fresh weight.

Walnuts also contain the ellagitannin, pedunculagin. Regiolone has been isolated with juglone, betulinic acid and sitosterol from the stem bark of J. regia.