Fortis Bengaluru nutritionist explains if onions with black spots are safe to eat; says throw them away if this happens
Are onions covered in black spots safe, or are they contaminated? If you’re unsure, is it best to err on the side of caution and discard them? In an interview with HT Lifestyle, Bharathi Kumar, nutritionist at Fortis Hospital, Nagarbhavi, Bengaluru, discusses whether onions with black marks are safe for consumption. Spoiler alert: it depends. Also read | ₹25″>Is the paneer in your bread pakora real? Doctor reveals truth about viral ‘quality check’ video of street food worth ₹25
Onions with black spots can be contaminated, but it’s not a straightforward yes or no answer. (Pic courtesy: Reddit/ curllyfries4)
Are black-spotted onions safe for you?
According to Bharathi, the black spots are usually caused by a common fungus that thrives in warm, humid conditions. While it’s not the same as the infamous ‘black fungus’ infection, it’s still a cause for concern.
She began by explaining: “Onion skins that are covered in black or have a dark, sooty coating are usually due to the surface-fungal growth of organisms like Aspergillus niger, a common environmental fungus that prefers warm, humid, and poorly-ventilated storage conditions where it can grow. However, these conditions are less severe than those caused by mucormycetes that lead to invasive ‘black-fungus’ infections.”
What causes the black spots on onions?
According to the nutritionist, “The outer layers of the onions become covered with dark, powdery spores which give them a sooty or charcoal-like appearance. Fungi generally infect onions when the skin gets hurt or moisture levels become quite high during transport and storage.”
Bharathi said, “The fungi that cause black spots in onions are not harmful in small amounts; however, they can produce ochratoxin A, a mycotoxin that causes kidney and liver toxicity when consumed in large quantities over a long time. The toxin is resistant even to moderate heat, so cooking does not necessarily destroy it. That is the reason why proper inspection and storage are of utmost importance before any culinary use.”
If the black discoloration spreads to the inner layers or the onion feels soft, mushy, or rotten, it’s likely contaminated and should be discarded to avoid potential health risks. (Made using Gemini AI)
When to discard onions?
If the black spots are limited to the outer skin and the inner layers are crisp and white, you can peel off the affected areas and use the rest. However, if the contamination is deeper or the onion is soft and mushy, it’s best to discard it.
Bharathi explained: “From a clinical standpoint, if the black discolouration is limited to the dry outer papery skin of the onion, and the inner layers remain crisp, white and free from visible dark streaks or soft spots, then the risk to a healthy individual is low, provided the onion is peeled thoroughly, rinsed, and cooked promptly. However, this reassurance comes with several important cautions.”
Bottom line: a little vigilance goes a long way in keeping your kitchen (and your health) in top shape. Here’s what you need to know:
⦿ Depth of contamination matters. “If the black colouring penetrates deeper into the onion, going through the layers and reaching the flesh, or if the onion is soft, moist, mushy, or even rotting, the chances of mycotoxin formation or outgrowth of more pathogenic species of microorganisms will be even higher. Nonetheless, in this instance, the onion should be thrown away,” Bharathi said.
⦿ At-risk groups require greater caution, Bharathi said and added, “People who have weak immune systems, uncontrolled diabetes, chronic lung or liver disease, or are receiving immunosuppressive drugs should not consume fruits and vegetables that are discoloured, mouldy, or spoiled in any other way. What may be safe for a healthy adult may still be a greater risk for them.”
⦿ Speaking of public perception and myth-busting, she said: “It is important to clarify that the presence of a black layer on an onion is not similar to the extremely rare and serious fungal infection mucormycosis (‘black fungus’), which affects internal tissues and has to do with totally different circumstances. Confusing one with the other creates unnecessary panic.”
⦿ Storage and handling are key preventive factors. According to Bharathi, “Onions should be kept in a cool, dry, well-ventilated place, away from dampness, sealed containers, and direct sunlight. Moist, unventilated storage allows fungal spores to germinate, and once the outer layers are compromised, the danger of further decay getting worse grows.”
She concluded, “For food businesses, restaurants, and households, it is sufficient to conduct these few simple checks while purchasing (firm texture, no damp pack, free ventilation) and use proper storage so that the risk is almost completely eliminated even before the onion reaches your menu or the chopping board in the kitchen.”
Note to readers: This article is for informational purposes only and not a substitute for professional medical advice. Always seek the advice of your doctor with any questions about a medical condition.
