Onions are often praised as a superfood that supports liver health due to their rich antioxidants and sulfur compounds. But that dark black streak or layer you sometimes spot inside an onion is a warning sign, not a harmless blemish. It may indicate fungal contamination that could harm your liver if consumed repeatedly.

Why onions turn black

The appearance of black or dark patches inside an onion usually signals a fungal infection, most commonly caused by Aspergillus niger . This fungus thrives in warm, humid environments and can invade onions during cultivation, transportation, or storage. Over time, the fungus produces mycotoxins, toxic compounds known to damage liver cells and impair detoxification processes in the body.

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