• Toni Miller
  • Dog Nutrition and Member Service Specialist

  • 3 mins read time
  • The Dirt on Mold

    Have you ever gone into your fridge to cook dinner or opened up a bag of dog treats only to find your food covered in bits of gray or blue fuzz? Mold is an unwanted guest in many people’s homes and is the main cause of food spoilage. Although we are all too familiar with it, most people don’t know much about it - especially when it comes to pet food.

    MOLD 101

    Mold is a type of fungi that lives on plant or animal matter, with a current estimate of more than 300,000 different species in existence. And although it seems crazy, mold spores are actually everywhere, and there’s no way to escape them! The tough part about mold is there are harmless species and harmful species, and without full lab analyses, it can be difficult to know which one you’re dealing with.

    Mold can only grow when a suitable combination of temperature, moisture, and available nutrients is met, and for the most part, many species won’t cause significant harm. Generally speaking, feeding a bit of moldy food to your pup will likely do no harm, and if at all, only cause a bit of digestive upset in the form of vomiting or diarrhea. And although it sounds strange, mold can actually be beneficial in some cases and can even prevent the growth of harmful bacteria! For instance, when salami is dry aged, a species of penicillium mold begins to grow on the exterior of the casing, forming a natural antioxidant barrier that protects the meat from harmful bacteria and rancidity. Typically, this species of mold appears white, though it can also appear blue/green. This is common not only in aged meats, but also in various types of cheeses as well (blue cheese, anyone?), and can actually enhance the rich flavors of the food.

    Mold can often sound a lot scarier than it is, which is why it's important to be informed about the different kinds of mold that affect pet foods and varying levels of mold toxicity in order to make educated decisions about what is safe to feed.

    Kibble - mold takes root fairly easily in kibble because of the high amount of grains and starches present in the food. Not only does the abundance of grains provide more than enough food for mold spores, but grain storage and packaging prior to production can also have an impact on overall mold growth and make the food more susceptible even before it reaches your home. For example, if grains are left to sit outdoors for long periods of time, moisture can develop and can make the food produced with those grains more susceptible to mold growth. The type of mold most commonly found in dry dog food is aspergillus or alternaria (read more below), and any affected food should be discarded due to how easily mold can spread and infect dry food that’s been contaminated.

    Canned Food - similar to any other canned item you would store in the fridge, canned or wet food is one of the best hosts for mold due to its porous nature and high moisture content. Though often stored in cooler temperatures, mold can still manage to creep in and take root - it might just take a little longer! If you see visible mold spores in any wet food, it’s best to toss the whole can. Mold only becomes visible once it’s established roots in the food, and when it comes to porous foods, there’s no way of cutting it out! If you find mold on wet food, it should be discarded, as wet food is moisture-rich and porous, which makes it easy for the mold to have taken root in the food before becoming visible to the naked eye.

    Air Dried Meat - air dried treats and chews that are 100% meat are somewhat less susceptible to mold due to having a majority of the moisture stripped away and being free of grains. However, any dehydrated or dried meat is still capable of harboring mold, especially when exposed to moisture from the environment or from your dog’s mouth! But don’t panic - dried meat is similar to hard cheese in the sense that it’s not porous, so cutting off the moldy bit can help you salvage the rest of the treat. Mold roots spread easiest in soft foods like yogurt or soft cheese, so if you catch it early, you can save yourself the heartbreak of throwing away your dog’s snacks! When it comes to mold prevention, storing air dried treats and chews in a cool, dry place (or in the freezer or fridge) can help drastically reduce the chance of mold.


    The very basic definition of mold is that they are fungi that live on plant or animal matter, with a current estimate of more than 300,000 different species in existence. To keep things simple, we will focus on mold primarily found in food.

    Aspergillus - commonly known as “black mold,” there are several hundred different species of this particular type of mold, but the most common ones affect things like damp walls and decomposing organic materials (including dry pet food). Aspergillus is one of several molds that can produce a special kind of mycotoxin - a poisonous substance naturally produced by some molds and fungi that can cause illness in pets and people.

    Penicillium - this genus of mold can grow on cured meat products and various kinds of cheese. Typically, this is a white colored spot you might see on salami or air-dried meat chew. They can be beneficial in some cases by actually preventing the colonization of undesirable fungi or bacteria. When this mold forms on a piece of cheese, for example, it has been long been accepted and safe to simply cut that part off and consume the rest of the cheese. However, certain species of penicillium molds can cause food spoilage and produce mycotoxins - though these harmful species are not the same as those used in food production. Penicillium citrinum is the common culprit of mycotoxin production, and is mainly associated with wheat, rice, corn, barley, oats, and rye. Spores from this type of mold can also trigger allergic reactions to those who are sensitive to mold. They typically produce bluish, greenish, and yellowish spores.

    Cladosporium - another common mold, this species is known for growing on things like cereal grains (which includes dry pet foods), fruits, and refrigerated meat. It typically is slow-growing and appears as black spots on foods which results in spoilage and discoloration.

    Alternaria - this type of mold is a plant pathogen, meaning it can cause lots of damage to agricultural products including grains, fruits, and vegetables. It is typically found outdoors on dead plants, cereal grains, and grasses. Similarly to Aspergillus and Penicillium, Alternaria is also capable of producing mycotoxins that can negatively impact animal and human health.


    Some molds are capable of producing toxins that can be harmful to humans and animals, namely called “mycotoxins.” Mycotoxins are a naturally occurring toxin produced by certain types of mold/fungi that can be found in food. One of the most commonly occurring mycotoxins is aflatoxin, which will be explained in more detail below.

    The main issue with mycotoxins is that they can cause severe illness, both short term and long term, after consumption of food products contaminated with the toxin. Long-term illnesses as severe as cancer and immune deficiency disorders in humans have been associated with mycotoxins, and symptoms of exposure in pets can include things like loss of appetite, jaundice, lack of energy, vomiting, and even death in severe cases.


    Aflatoxins are some of the most poisonous mycotoxins and are often produced by aspergillus molds. They commonly grow in soil, decaying vegetation, hay, and grains, and can often affect foods like cereals (corn, wheat, rice), spices, and tree nuts. Unfortunately, due to the nature of commercial pet foods today, pets are more susceptible to these toxins than we think, simply due to the overwhelming presence of grains in many dry foods. Just like any other strain of mycotoxin, aflatoxin poisoning can cause GI upset, anemia, jaundice, and is even linked to cancer.

    Ingredients like corn, wheat, and rice are still very common sources of protein in many brands of dry pet food today, and can be at a higher risk of aflatoxin contamination compared to foods made with more meat protein. As mentioned earlier, the conditions under which crops are stored can influence mold growth, which can then lead to toxins being introduced to the pet food when contaminated ingredients are used during production. It can also be difficult to know if your dry food is contaminated with mold because it is not always visible upon opening the bag - sometimes mold growth starts from the bottom, where you wouldn’t see it until you’ve already fed some of the food.

    So how do we protect our pets from aflatoxins? Your best option would be to switch to a fresh food diet low in carbohydrates, as these types of diets are at a lower risk of mold contamination compared to dry foods that include cereal grains. However, switching to fresh food isn’t an option for everyone, which is why it’s important to emphasize the importance of checking the ingredients in your pet’s dry food. Because aflatoxins are often found in cereal grains, it is best to avoid pet foods that include ingredients like corn gluten meal, whole grain corn, corn flour, sorghum, rice, wheat, and maize. Not only are they a source of unnecessary carbohydrates, but they could be contaminated with mold too!

    Additionally, storing your food properly will help eliminate potential risk of molding in your treats, chews, and other food, so keep reading for helpful mold prevention tips!


    Even though not all mold is harmful, it’s best to prevent mold growth from the beginning when you can! Here are some useful tips on how to keep your fresh food and treats fresh until you feed.



    SEAL IN THE FRESHNESS. Whenever you buy fresh, air-dried or freeze-dried treats, they usually don’t come with any preservatives. This is amazing because it means you are feeding real food! But it also means you need to pay close attention to “best by” dates. For example, each treat and chew from Real Dog Box has an info card with tips for proper storage and estimated “expiration” dates, so if you know your pup won’t finish their treats and chews within a month or two, ALWAYS pop them in the freezer.


    KEEP IT CLEAN. When storing dry food, it is best to get an airtight container to put your food in to keep critters and mold spores from making their way into your dog’s food bag. Always be sure to periodically wipe out your container with soap and water to keep any potential bacteria from building up between refills.

    STORE IN A DRY PLACE. Moisture is your worst enemy when it comes to mold growth, so always be sure to keep your dry food away from water or other forms of moisture! Ensuring that your food stays dry will help preserve it longer and make it less susceptible to mold growth.



    DRY IT OUT. Lots of people like to give their dogs bigger chews in multiple chewing sessions. And while this is perfectly okay, it’s important to make sure you are letting the chew dry out before placing it back in the freezer or fridge. Mold loves moisture and is capable of growing at fridge temperatures, so reducing the amount of moisture on the chew is the first step to combat this unwelcome guest.

    DITCH THE ZIPLOC. Not only is it a good idea to cut back on using plastic bags for the sake of the environment, but they also aren’t doing your pup’s chews a lot of good either when it comes to proper storage. If your dog has had at least one chew session, you will want to follow step one first, and then proceed to wrap the chew in parchment paper before placing it in the freezer or fridge. Zip-locs and other plastic bags can seal in moisture, which can then trap the chew in a damp environment with no way of air drying - the perfect recipe for mold growth.


    USE IT OR LOSE IT. Wet food or any kind of moisture-rich food like raw can be highly susceptible to mold growth due to the high moisture content, so it’s important to be aware of when you opened a can before feeding more of it. After opening wet food, always be sure to store it in your fridge and use it within about a week to ensure it is still fresh when you feed it. If you are feeding raw food, you can always re-freeze it if you won’t be able to use it up in time, which will help prevent spoilage and increase the food’s shelf-life!

    FREEZE IT. If you have a small dog, or a dog that takes days to get through one wet food can, you can always freeze the food left in the can to preserve it until the next meal time. Not only does this help reduce the chance of molding, but it allows you to store wet and fresh food for longer periods of time, up to several months, compared to just a few days.

    In summary, there are tons of species of mold out there and it can be difficult to know what to do when you find mold on your dog’s treats or food. Most of the time, mold will just cause mild digestive upset, but it’s important to be aware of the potential harm that mycotoxins and aflatoxins can cause if ingested. And remember, proper storage and sanitation can help reduce the chance of food spoilage, and will keep your dog’s food fresher longer!