Mold On Onions: Black Mold & Powdery Mildew Still OK To Eat?

Nobody wants to come home after a trip to the grocery store to find little black powdery spots all over their freshly bought onions. So, the question is, can you still eat onions that have got a little mold on them?

You should not eat onions that have mold growing. Some fungi can produce mycotoxins which are harmful to animals and humans when ingested or spores from the mold are inhaled. Mold growth also indicates spoilage, meaning the onion is already well past its best.

In this article, we will be answering all these questions and more, so, for everything you could ever need to know about mold growth on onions, keep reading.

black mold on onion

Are moldy Onions safe to eat?

Unfortunately, no, moldy onions are not safe to eat as the fungi growing can produce mycotoxinsOpens in a new tab. which can cause serious illness in people with allergies or weakened immune systems, and can even cause unpleasant symptoms in those with otherwise healthy systems.

Not only are the onions not safe to eat, but the experience of eating them would not be pleasant at all. When an becomes moldy, it means that it has already begun to spoil, which means that mold is not your only concern, as bacteria have already started to break down the onion’s tissues making it mushy and slimy.

These bacteria can also cause serious gastrointestinal issuesOpens in a new tab. if consumed in large enough quantities, as well as giving the onion a bitter taste and very unpleasant smell.

Is it okay to eat an onion with mold on the outside?

Mold on the outer layer of the onion is often a strain caleld Aspergillus nigerOpens in a new tab., which can indeed cause symptoms in those with allergies.

Finding black spots on the outer surface of an onion is by no means uncommon, and luckily there is nothing to be concered with. As long as you peel the outer layers off and remove the first layer of skin, the exterior mold will not harm you, and the onion can be used.

If you have mold specific allergiesOpens in a new tab. however, it would be best not to touch the onions and to discard them, as spores can tavel through the air and can be inhaled, causing symptoms. If the mold looks like it may have traveled further into the onion, you are best off throwing it away.

Much as this may seem wasteful, mold is a complex system, and if it is large enough to spot with the naked eye, you can be certain that its spores have already traveled all over the onion and have already begun to settle on other parts and may have begun to create roots or “hyphaeOpens in a new tab.“. These roots are thin, thread-like strands that burrow deep into whatever surface the mold has grown on to absorb moisture and nutrients amongst other things.

These roots can distribute mycotoxins throughout the onion and even if you think you have removed all traces of mold, invisible mycotoxins can still be present in what otherwise looks like perfectly fine onion.

What happens if you eat moldy onions?

In the majority of cases, accidentally ingesting a small amount of mold is unlikely to cause major harm if you have a fully functional immune system. For weakened immune systems, symptoms of nausea, gastrointestinal discomfort, headaches, and nausea could result from eating moldy onions.

If you were to realize after eating one onion that several others you purchased at the same time have mold growing on them, there is little you need to do. It is not advised to induce vomitingOpens in a new tab., as this can cause injury and is not only not needed, but would not necessarily remove mycotoxins from the body if they have been ingested.

Instead, you should check for symptoms or any feelings of discomfort immediately after eating the onion, if any present themselves, you should seek medical advice to rule out food poisoning. If there are no immediate signs of allergic reactions or illness, monitor yourself over the next few days and seek medical advice if it is required.

Can you still use onions with mold?

We’ve explained that using onions with mold growing on them is best avoided, but you may still be wondering if you can still eat the onion if it is cooked or used in any other manner than raw.

The answer is, I’m afraid, the same. You should not be using moldy onions, even if you were to cook them.

This again is a result of the bacteria (that are almost certainly present if there is visible mold growth), breaking down the structure of the onion, turning it mushy in texture, bitter in taste, and sour in its smell.

You would be correct to assume that cooking a moldy onion would kill bacteria and most strains of mold, however, the harmful compounds fungi produce (mycotoxins) can be very resilient to heatOpens in a new tab. and may still be present after cooking.

I understand that some people might prefer to use a video so they can see how to clean an onion with mold on it and when it can still be used, so I’ve added the video below to make things a little easier.

Can you cut white mold off an onion?

Surely if you see mold, be it white, green, black, or any other color, you can cut it off and still eat the fresh parts? Well, once again, unfortunately not.

The reason for this is that even if you think you have removed most of, (if not all) the mold from your onion, there is a very good chance the mycotoxins have already been spread throughout the onion and can still cause harm if eaten.

The other factor is that when in their developing stages, fungi are invisible to the naked eye, so you would not be able to tell if microscopic formations were present.

Essentially, it is incredibly difficult to be 100% certain that you are actually removing all the mold, even if it looks good enough to eat, so it’s not worth the risk.

What causes mold on onions?

There are two primary causes of mold growth occurring on onion bulbs and plants, improper storage conditions and downy mildew occurring during cultivation.


Onions must be stored in dark dry conditions after harvesting, as moisture levels greater than 70%Opens in a new tab. will quickly lead to mold and mildew growth. Likewise, the temperature needs to be carefully controlled to prevent not only mold but bacteria growth. Temperatures of 32-40 degrees Fahrenheit (0-5 Celsius), should be maintained to keep onions at their most fresh.

Under perfect storage conditions, onions can be kept in storage for up to one year.

Powdery mildew

Onions, beans, artichokes, parsnips, and many other varieties of vegetables are affected by powdery mildews, a type of fungus, most often the Podosphaera xanthiiOpens in a new tab. strain from the Erysiphaceae family.

Comfortable temperature ranges for powdery mildew are between 68-86 degrees FahrenheitOpens in a new tab., with humid environments speeding up the growth of the fungus, which makes warm wet summers typically to blame for powdery mildew growth. However, improper storage conditions that create high humidity can also promote growth or exacerbate existing growth.

What type of mold grows on onions?

Common strains are PennicilliumOpens in a new tab., which appears with blue or green patches, AspergillusOpens in a new tab., which is seen as dark, powdery spots, BotrytisOpens in a new tab., also known as “Grey rot”, which appears as grey, fluffy patches and RhizopusOpens in a new tab., which appears as soft black patches on onions.

Penicillium and Aspergillus both have the ability to produce mycotoxins or aflatoxinsOpens in a new tab. which are known to be harmful. Whilst these are the most common strains seen growing on onions, there are many others that could grow if the circumstances were correct.

Is black mold on onions dangerous?

The black “soot-like” substance found on purchased onions is caused by a fungus named Aspergillus niger, which is often found within the soil the plant was grown in.

This strain is often mistaken for black mold due to its dark hue, however, this is rarely the case, and Aspergillus niger is far more likely to be the cause rather than the “true” black mold, Stachybotrys chartarumOpens in a new tab..

Aspergillus niger is often seen with dark colorations such as very dark brown, dark grays and of course, black. It’s usually described as having a velvety or cotton-like texture, although it can also become powdery over time.

What is the white fuzzy mold on my onions?

The most likely cause of white fuzzy mold growing on your onions is a strain of fungi called Sclerotium cepivorumOpens in a new tab., also known as “white rot”. This strain often appears with a white or light coloration and has a fuzzy or fuzzy texture.

This strain can quickly begin to rot the onion, making it unsafe to eat. There is no safe way to use an onion that has white rot on it so it should be discarded.

Is the mold dangerous?

Inhalation of aspergillus niger spores by healthy individuals is usually harmless, for people with weakened immune systems, caution should be taken, as inhalation, ingestion, or coming into direct contact with the mold or its spores can lead to symptoms such asOpens in a new tab.:

  • Asthma Attacks
  • Gastrointestinal discomfort
  • Nausea
  • Rash

It is recommended to have as little contact as possible with molds and their spores. This is because it can be extremely difficult to ascertain the strain of mold by vision alone, and so despite the high likelihood of aspergillus niger being the culprit for onion mold growth, you will not be able to tell for certain, and you may in fact be dealing with a strain of higher toxicity.

How to store onions to prevent mold growth

Onions are stored for many months before they reach the grocery stores where the public can purchase them, mold growth can occur during this time, so a very simple method to ensure that the rest of your onions do not become moldy, is to be careful whilst you are purchasing them.

Be on the lookout for small patches of what looks like black powder on the external skin of the onion, as well as any soft patches. Mold can quickly spread from one onion to another, so it only takes a single moldy onion to affect a whole string.

Washing onions that show any signs of exterior mold growth can be helpful in preventing them from spreading to other onions or being stored loose. However, be very careful to make sure they are completely dry before storing them.

You should also aim to keep your onions as dry as possible, this means not storing them in the refrigerator, as they are high-humidity areas, instead, keep them in an open basket, and If at all possible, keep them in a dark, well-ventilated area, such as a pantry with air vents. This will allow them to last longer whilst maintaining their characteristics.

When should you throw away moldy onions?

When blue-green, white, or any other color of mold is seen growing on the outer skin or within the core of an onion, it should certainly be discarded. Eating an onion that has this level of mold can lead to unpleasant symptoms of mold exposure that can be otherwise easily avoided.


Do onions go moldy in the fridge?

Onions will become moldy faster in a refrigerator than they would if they were to be kept on a kitchen counter. This is because refrigerators are high-humidity environments and unpeeled onions can quickly absorb the moisture that mold needs. A lack of ventilation further exacerbates this issue by trapping moisture.

What is the grey mold on your onions?

Gray mold formation on onions is the result of Peronospora destructor, a strain of powdery mildew. Onions and shallots are most commonly affected by the pathogen, with chives and leeks less often. Warm and moist conditions make powdery mildew growth more likely. Any items found with powdery mildew growth should be discarded.

How long does it take for an onion to mold?

Mold can form rapidly on an onion when the correct conditions are met. With adequate moisture levels and temperature ranges, mold and mildew can begin to grow within 6-12 hours, with visible mold growth becoming present within 1-2 days.

What does mold on an onion look like?

Onion mold can be white, black, or green, with black mold often appearing in small clusters of circular dots with a powdery texture. White mold is frequently a symptom of a serious condition called white rot, which can be seen as a white fluffy growth originating from the base of the bulb.


Mold growing on onions is a common occurrence that often begins during the cultivation of the onion plant, or whilst storing. Aspergillus niger is often mistaken for black mold and is usually harmless to people with healthy immune systems.

Over to you

I hope this article has given you some guidance on whether or not it is safe to still eat onions if they have a little mold on them, as well as highlighting some of the risks doing so could carry. Now I’d like to turn it over to you, have you ever eaten moldy onions, accidental or not? Do you have any storage tips you use to keep your onions fresh for longer and how do you deal with finding mold growing on them, do you throw them away or still use them?

I’d love to hear about your experiences, so please leave a comment below and I will get back to you ASAP.

Chris Walker

Chris Walker has struggled for several years with mold after buying his own property. After finding the solutions to several issues around his home, he decided to create this site in order to answer as many questions about mold and mildew as possible to help others dealing with the same problems.

Recent Posts