Skip to Content

Wet Insulation | Is It Bad for Your Health?

Insulation is meant to be securely placed between the walls of your home, away from all possible sources of moisture. Unfortunately, things don’t always go to plan. Leaky roofs, ground moisture, and plumbing leaks are just a few causes of wet insulation.

Wet insulation is not only less effective (or even completely ineffective), but it also poses a number of direct and indirect health risks.

Wet insulation is harmful to health. It may harbor dangerous levels of mold and bacteria. Off-gassing of formaldehyde can cause respiratory irritation. Animals are attracted to the warm, moist environment and can spread infectious diseases to inhabitants.

Direct Impact on Health


We are surrounded by bacteria all the time, and this isn’t necessarily a bad thing. Some bacteria are helpful to our bodies. However, wet insulation may harbor harmful bacteria that can lead to illness.

The ideal breeding grounds for bacteria include nutrients and moisture. When insulation becomes moist, bacteria start to grow exponentially faster than they would on dry insulation.

Any small colonies that were found on the insulation before it got wet now have the chance to grow rapidly. These bacteria may not have been a health risk when found in small quantities, but larger quantities can overwhelm your immune system.

The most abundant bacteria families found in homes include Staphylococcus, Streptococcus, and Corynebacteria families. If these bacteria are allowed to grow unchecked, they can lead to life-threatening diseases in some cases. 

The most abundant bacteria families found in homes, streptococcus,  staphylococcus and corynebacteria

MRSA, or Methicillin-resistant Staphylococcus aureus, is a strain of Staphylococcus bacteria that is resistant to antibiotics. It is increasingly being found in homes and can cause painful skin abscesses.

Group A Streptococcus is a bacteria that is found in the nose and throat, often without any adverse symptoms. However, if this bacteria is allowed to breed large colonies on wet insulation, it can cause illnesses such as strep throat, impetigo (skin infection), pneumonia, and toxic shock syndrome.


In addition to bacteria, mold may become a health issue if your house has wet insulation

Mold grows when its spores are released through the air and land in environments with suitable conditions. Mold spores can be introduced to your home by being carried in on shoes, clothes, pets, etc. 

Once mold spores enter your home, there are many places that are suitable for mold growth. Mold prefers dark, moist, and warm environments with suitable nutrients. 

Unfortunately for us and our homes, mold can derive nutrients from building materials such as wood, cardboard, carpet, ceiling tiles, and, you guessed it, insulation. Once insulation in enclosed walls gets wet, it’s only a matter of time before mold growth starts.

Some of the most common mold varieties found in homes include Cladosporium, Penicillium, Aspergillus, and Stachybotrys. You may not know these molds by their scientific name, but perhaps the term “black mold” rings a bell.

Although common, mold varieties such as Stachybotrys are cause for concern when found in your home. They can cause symptoms such as eye irritation, respiratory distress, adverse pulmonary effects, and congestion.

In extreme cases, mold sickness can even lead to memory loss and secondary illnesses, such as pneumonia.

Since insulation is enclosed in your walls, you may not be able to see the mold before you start experiencing symptoms. It is important to prevent moisture from entering your insulation before and after it is installed in your home. 


Even without mold or bacteria, wet insulation can be harmful on its own through the process of off-gassing. 

Off-gassing occurs when a product deteriorates and begins to release dissolved chemicals into the air. 

Fiberglass, mineral, and wool insulation often contain formaldehyde to help bind the insulation fibers together. When formaldehyde gets wet, it begins to off-gas.

Off-Gassing due to wet insulation and fiberglass, mineral, and wool insulation containing formaldehyde

Formaldehyde gas is corrosive. It can deteriorate metal studs, wall ties, and roof fasteners, which compromises the integrity of your home.

The health risks of formaldehyde gas is another major concern. It is a known carcinogen, and wet insulation can release formaldehyde at a rate of 32 PPM. This concentration of formaldehyde can cause the following symptoms:

  • Watery, burning eyes 
  • Nausea   
  • Skin irritation                                                                                                               
  • Upper Respiratory Irritation                                                                                      
  • Lower airway and pulmonary effects

Urea-formaldehyde foam insulation (UFFI) has been used since the 1950s. Since we now know more about the harmful effects of formaldehyde, most modern spray foam insulation products do not contain this chemical anymore.

However, if you were not the one to install the insulation, you may not know for sure whether or not the insulation contains formaldehyde. And even if the insulation in your home does not contain this chemical, it must not get wet to prevent mold and bacteria growth.

Indirect Risk to Health

The health risks associated with wet insulation don’t stop there. The related consequences of wet insulation can create even more health risks.

Critters love the warm, moist environment created by wet insulation. Animals will likely enter through the same opening that water entered the insulation, so the type of animal that nests inside depends on the size of the opening.

Dirty mineral wool insulation in the attic

The most common animals to nest in insulation and their related health risks include the following: 

  • Birds and bats: People who inhale fecal matter from birds and bats may contract histoplasmosis, an incurable respiratory disease characterized by flu-like symptoms.
  • Raccoons: Raccoons can carry infectious diseases such as rabies. Their feces is often infected with a roundworm known as Baylisascaris. If inhaled, the roundworm eggs can cause irreversible damage to the brain, heart, and eyes.
  • Squirrels: Squirrels carry diseases such as ringworm, Lyme Disease, and rabies.
  • Insects: Feces, saliva, and body parts from cockroaches can aggravate asthma and allergies. Pests also carry food contamination illnesses.

These animals are often infected with ticks, fleas, and bedbugs. Once brought into the home, these parasites may look for new hosts, such as pets and people.

If animals die in the insulation, they will not only smell terrible but also may release harmful gasses as they decompose. The corpses attract even more pests such as flies and fleas.

There are also other risks as well as smells and loss of efficiency associated with wet insulation.

One Possible Benefit

Wet insulation is clearly bad for your health, in addition to being useless at actually insulating your home (sometimes you can dry it and reuse it). 

However, if you are handling old insulation that needs to be replaced, you may consider wetting the surface of the insulation so that it is less likely to release dust particles and material fibers such as fiberglass into the air.

These particles can trigger allergic reactions. Wetting the insulation in this case may be the lesser of two evils for you as it will limit the possibility of allergic reactions.

You must keep in mind the off-gassing of formaldehyde, but if you are only around the insulation for a short period of time this is not a large concern.


Was this helpful?

Amazon and the Amazon logo are trademarks of, Inc, or its affiliates.