How Much Mold Can Make You Sick?

David J. Allen

I spent the better part of 2 ½ years learning about mold and indoor air quality because my child's life depended on it. Now I help others avoid ever having to experience the same thing. The mold industry suffers from conflicting opinions and I do my best to distill loads of data into something practical and useful. I love hearing from and helping readers. • "A house desecrated by mildew, mold, or fungus would be a defiled place to live in, so drastic measures had to be taken." — Leviticus 14:45

There is no hard and fast rule on how much mold it takes to make a person sick.

Exposure to mold can cause one person in a home to develop a “stuffy nose, sore throat, coughing or wheezing, burning eyes, or a skin rash,” while another person living in the very same home may have no adverse reaction or symptoms at all.

People react very, very differently to mold. (Your spouse is not crazy—there is a mold problem in your home.)

Generally speaking, women tend to be more affected by mold exposure than men are, but even this is not a hard and fast rule, nor is it necessarily the most important demographic distinction for mold reactions.

If you are exposed to mold, whether in your home, car, or workplace, a number of variables may be factors in whether or not you will experience any adverse effects.

[For informational purposes only. Consult your local medical authority for advice. Sources: U.S. Centers for Disease Control and others.]

More importantly, these groups of people are generally more affected by mold and are advised to avoid mold:

Persons at Higher Risk of Mold Sensitivity: “People at Greatest Risk from Mold”

The following groups of individuals are, according to the U.S. Centers for Disease Control and Prevention, the “People at Greatest Risk from Mold.”

“People with asthma, allergies, or other breathing conditions may be more sensitive to mold.”

U.S. CDC, “Mold After a Disaster,” last reviewed by CDC on July 28, 2020.
  • “People with immune suppression (such as people with HIV infection, cancer patients taking chemotherapy, and people who have received an organ transplant) are more susceptible to mold infections.” (U.S. CDC, emphasis added.)
  • “People with weakened immune systems can develop invasive mold infections days to weeks after exposure to fungi that live in the environment.” (U.S. CDC, emphasis added.)
  • “People with a weakened immune system, especially people receiving treatment for cancer, people who have had an organ or stem cell transplant, and people taking medicines that suppress the immune system, should avoid cleaning up mold.” (U.S. CDC, emphasis added.)
  • Children should not take part in disaster cleanup work.” (U.S. CDC, emphasis added.)
  • “People with weakened immune systems and with chronic lung diseases, such as obstructive lung disease, may develop mold infections in their lungs.” (U.S. CDC, emphasis added.)

How Does Mold Exposure Happen?

By far the most common way that people are exposed to mold is by unknowingly breathing in mold spores.

Mold spreads by distributing many of these microscopic spores into the air, and when they’re floating around room you’re in, you can inhale them without even realizing it.

So, in many cases, there will be a mold infestation lingering in a hidden corner of a home, and the residents will be regularly breathing the spores for days, weeks, months, or even years without being aware that the fungus is there.

Moldy hates the sun with a passion, and it tends to hide in areas that are damp and dark, such as behind walls, inside bathroom vanities, and other hidden areas.

Out of sight, it’s also usually out of mind, until it causes noticeable problems to a building or the people inside of it.

The first evidence of a mold problem is usually the smell that mold gives off—which is best described as dirty socks or a musky, earthen odor—and at that point, the smell is actually caused by (or accompanied by) mycotoxins, which are even smaller than mold spores and which are produced by certain molds.

The other, less common way that you may be exposed to mold is by unintentionally ingesting it.

For example, if you’re casually eating a bowl of strawberries, you may accidentally eat one that has mold on it.

If the amount of fungus is small enough, you may even chew and swallow the food without noticing it.

Variables That Come Into Play

A number of variables may influence how much a person is affected by mold.

Various genetic dispositions, not all of which are yet fully known or understood, can influence how much a person is affected by mold and in what ways it manifests.

Certain groups of people should also have as little contact with moldy environments as possible, and should never take part in mold remediation of disaster cleanup. (See list above, “Persons at Higher Risk of Mold Sensitivity.”)

  • Children
  • The elderly
  • Pregnant women
  • Persons with asthma, allergies, and breathing conditions
  • Cancer patients undergoing chemotherapy.
  • Persons on immunosuppressant medication(s).
  • Organ donor recipients and stem cell recipients.

Variable: Mold Allergies and Sensitivities

For the average person with no allergy or particular sensitivity to mold, a one-time or occasional exposure to a small amount of mold may not result in any symptoms.

But for the many people who do suffer from mold allergies, it often takes very little exposure to have negative effects on their health.

If you’re allergic to mold, your immune system sees mold spores as allergens, and inhaling even a small amount of them can lead to unpleasant allergy symptoms like sneezing, nasal congestion, coughing, and itchy eyes, nose, and throat.

That isn’t to say that only people with mold allergies will be affected by exposure to the fungus, but the amount required to experience symptoms will vary from person to person.

It’s also worth noting that certain demographics are inherently more sensitive to mold exposure.

Namely, studies have shown that infants, toddlers, children, and the elderly may be more likely to experience adverse health effects after coming into contact with mold spores.

So, if a healthy, allergy-free adult and a young child were to inhale a similar quantity of mold spores, it’s quite possible that only the child will get sick.

Variable: Proximity to the Mold

If you inhale mold spores, one of the biggest factors to determine whether you get sick will be the proximity of your exposure: How close are or were you to those mold spores, and for how long.

If you’re working directly with mold, whether inspecting it closely or attempting to remove or clean it, you’ll be much more likely to get sick than if you’re simply in the same room as a mold colony.

This is primarily because the closer you are to the actual mold, the more spores you’re likely to breathe in, and more spores generally mean a higher probability of experiencing symptoms.

Fresh, moving air dilutes the concentration of mold spores in an area, which is one reason why opening windows can help resolve a mold problem—though it alone will never remediate a mold problem.

For this reason, it’s extremely important that you always wear the proper protective equipment any time you’re working with mold.

At the very least, you should use rubber gloves, safety glasses or goggles, and a facemask or respirator.

Variable: Duration of Mold Exposure

Another variable that plays a big role is the duration of the mold exposure: How long did it last?

The longer you spend in a room with mold growth, the greater your chances will become of becoming sick.

The reason for this is pretty straightforward: The more time you spend exposed to mold, the more spores you’ll have the opportunity to inadvertently inhale.

Assuming you aren’t working directly with the fungus and don’t have a mold allergy, you probably won’t notice any symptoms from being in a room with mold for a day or two.

However, if you were to have a large mold colony hidden in your bedroom for several weeks or months, there’s a strong possibility that you would start to feel sick eventually.

Common Symptoms of Mold Exposure

The specific symptoms of mold exposure will vary from person to person.

Every person’s body reacts differently to the spores, and different types of mold can cause different health issues.

For example, some mold species are allergenic, while others are toxigenic and produce harmful mycotoxins that cause more serious symptoms.

“Mold can cause many health effects. For some people, mold can cause a stuffy nose, sore throat, coughing or wheezing, burning eyes, or skin rash. People with asthma or who are allergic to mold may have severe reactions. Immune-compromised people and people with chronic lung disease may get infections in their lungs from mold.”

U.S. Centers for Disease Control, “Mold,” Last Reviewed: November 14, 2022

Listed below are some of the most common symptoms that people experience if they’ve been exposed to mold spores.

  • Nasal congestion or irritation
  • Sneezing
  • Coughing
  • Wheezing
  • Shortness of breath
  • Sore throat
  • Itchy or watery eyes
  • Skin irritation
  • Nosebleeds
  • Blurry vision
  • Red eyes
  • Digestive issues
  • Headache
  • Unexplained muscle cramping
  • Asthma attacks
  • Fatigue