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Beware: Black Mold and Pets

Black mold loves to grow in humid areas around the home. Make sure you are protecting your entire family against this common household threat.

Pets can develop skin rashes and sores when faced with black mold in their living quarters. By: larrison

Is black mold making your pet (and you) unwell?

Black mold is seriously unpleasant. It lurks in your home, in a poorly ventilated bathroom or along a damp window frame. Wherever there’s condensation or a damp wall, black mold is never far behind.

But what many people do not realize is just how bad black mold is for the health your pets — and you.

What Is Black Mold?

Black mold belongs to the fungal family. Fungi make up 25% of our planet’s biomass, and they are very diverse, including mushrooms, toadstools, molds and mildews. What unites them all is a lack of chlorophyll.

Although many fungi are harmless, there are also some extremely unpleasant family members, such as aspergillus, which cause serious infections.

Black mold loves to grow on cellulose, which includes substances such as straw, grains, paper (including wallpaper) and wood. It thrives when that substrate has a relative humidity of 15% and the ambient environment is around 90% (hello, bathrooms). But basically it will take advantage of anywhere that water has got in, so a leaky roof, faulty damp-proof course or a cracked drain are all open invitations to black mold.

Black mold facts:

  • It is a fungus called Stachybotrys chartarum.
  • Black mold poisoning is called stachybotryotoxicosis (literally “poisoned by stachybotrys”).
  • Black mold is in part responsible for “sick building syndrome,” where people develop respiratory difficulties, chest tightness and headaches.

A Short History

Black mold has been known to cause problems in farm animals, but it’s only in the past decade that awareness has risen about ill health in our domestic pets.

This fungus thrives in damp straw. Animals bedded on infected straw can suffer from a range of symptoms and syndromes, from sudden death in horses to diarrhea in cattle and uncontrollable tremors in pigs.

Indeed, in the 1930s, black mold was recognized as causing skin problems in Russian farm workers. These laborers bedded down on damp straw in a barn and developed itchy red skin rashes, ulcers and sores. The cause of the rash was confirmed by rubbing the moldy straw on undamaged skin.

It transpired that the black mold gives off a toxin (trichothecene mycotoxin) that damages cells, which, in this case, happened to be skin. The chilling part is that those toxins can damage any body tissue it contacts, including the liver (via the bloodstream) and lungs (by breathing the fungus in).

Bathrooms are a common breeding ground for black mold. By: apardavila

Black Mold and Pets

Black mold hit the news in 2007 when a veterinarian diagnosed it as responsible for the death of 2 cats. The cats had undergone routine dental attention under anesthetic, only to die from fatal lung hemorrhages.

How could this happen, and what is the link?

Black mold produces a mycotoxin (a toxic chemical produced by a fungus) that, when circulated in the bloodstream, causes cell death and damages the liver. Crucially, this mycotoxin can damage the liver’s ability to produce blooding clotting factors. This means the patient has difficulty clotting blood, with symptoms such as nosebleeds, blood in bodily waste or fatal hemorrhages from the lungs.


The symptoms of black mold infection in pets range from allergic type sniffles to joint pain and blood clotting problems.

  • Runny nose
  • Sneezing
  • Nosebleeds
  • Lameness (because of bleeding in the joints)
  • Skin rashes and sores (on thin-furred areas such as the belly or armpits in pets)
  • Loss of appetite
  • Lethargy
  • Trembling
An extreme case of dangerous black mold overtaking a home. By: satemkemet


The treatment may involve a blood transfusion (if the pet bleeds unduly) and antibiotics to fight secondary infections. Your vet will repeat blood tests to monitor liver function. The pet must rest to reduce the risk of knocks and bumps, which could cause bleeding.

It is crucial to get rid of the black mold or stay away from it. Remember, this is a condition that affects pets and people, so if your cat or dog is unwell, then you must leave that environment and seek urgent medical help for yourself, too.

And Finally…

The chilling conclusion is that black mold in the home is potentially very dangerous indeed. Not only could your pets be at risk, but also it poses a threat to human health.

If you have black mold in your home, be alert to the risks and get rid of the mold. If you or your pet have allergy-type symptoms or feel unwell in any way, see a physician or veterinarian immediately.



This pet health content was written by a veterinarian, Dr. Pippa Elliott, BVMS, MRCVS. It was last reviewed Oct. 13, 2018.