Mold Statistics

Quick Summary

Indoor mold affects millions of American households every year. Not only does mold cause costly damage to personal property, but many people experience ongoing respiratory issues due to chronic dampness and mold growth. Mold problems don’t just affect your home—mold infestations cost the US economy billions of dollars in repairs and health care costs each year.

Mold Statistics Overview

Mold is a common but devastating problem for homeowners. Mold growth begins with dampness inside buildings, which provides the perfect environment for mold spores to spread.

Left untreated, mold releases spores and mycotoxins, which worsen indoor air quality. Exposure can have a variety of health effects, increasing rates of bronchitis, allergic reactions and immune system irritation.

Medical experts say it’s even known to exacerbate some respiratory conditions.

Rates of Indoor Mold Growth

Mold problems are very common in the United States and worldwide. Mold growth is typically started by water damage or dampness, typically in the ceiling tiles or drywall. Water is the main requirement for mold to grow, as mold can pull nutrients from the air or the building materials it lives on.

In a review from the World Health Organization, dampness is estimated to be present in 20-50% of homes in the US.

Residential and commercial buildings without sufficient ventilation, heating or insulation are most likely to have mold, totaling around 45 million homes and buildings. Globally, around 30% of homes are impacted by mold, according to the WHO.

Mold issues are caused by a variety of mold strains, the most common being filamentous fungi. Mold is different from mildew—a surface-only fungi, which can be cleaned with a sponge and water—while mold is deeper, and moldy spots usually indicate a full infection.

Here are the differences between mildew and mold types:

All of these types of mold can grow quickly in damp, humid environments, and can damage homes and health.

Mold and Health Effects

Mold exposures are leading causes of environmental health problems. Toxic mold emits spores and creates indoor air pollution that can lead to illness.

Top illnesses related to toxic mold include stuffy nose, itchy or red eyes or allergic and asthmatic reactions in people with preexisting conditions, according to mold FAQs prepared by the Centers for Disease Control and Prevention.

In 2007, the WHO concluded that dampness and mold are associated with almost a 30-50% increase in rates of respiratory illnesses.

Often, outdoor air quality and pollution is considered as a source of allergens, but these problems can also originate inside. The health issues caused by long-term exposure to mold are very serious.


A study by the Environmental Protection Agency estimated about 4.6 million cases of asthma in the US are directly caused by mold. The WHO concurs with these findings, reporting that as many as 21% of American asthma cases could be associated with dampness and mold.

Asthma is a condition that involves swollen and inflamed airways, and more mucus in the lungs and sinuses than is normal. People with asthma can struggle to breathe normally and catch their breath after exercise. Mold makes asthma worse by irritating and inflaming the lungs with spores, which makes it even harder to breathe.

The EPA also points out that asthma attacks can be more common in homes with mold. When mold environments are improved, asthma-related symptoms like coughs or wheezing are reduced by 25-45%, according to the WHO.


Prolonged exposure to mold can also worsen a mold allergy. According to the CDC, those with allergies can be the most sensitive to indoor fungal infections.

In a 1999 report, the Mayo Clinic found that 96% of patients with chronic sinus infections have these infections as a direct result of mold overexposure.

Symptoms of mold allergies include:

  • Hives
  • Cough
  • Itchy or watery eyes

Allergies are caused by over-reactions of the immune system to outside particles, so when an allergic person inhales mold spores, their body reacts very negatively to it.

Other Respiratory Diseases

Mold exposure is also responsible for worsening other respiratory conditions, like COPD or COVID-19. These conditions weaken the lungs, and make them even worse in responding to mold spores in the air. Other conditions, like Aspergillosis, are caused by mold exposure.

Aspergillosis is a developed sensitivity to Aspergillus mold, and can even lead to mold growth inside the lungs in very extreme cases, according to the American Lung Association.

Impacts and Losses Due to Mold

Mold damage has massive economic, financial and social impacts on those affected.

According to a review published in the Journal of Environmental and Public Health:

  • Mold-related infections cost the US economy about $5.6 billion per year
  • Asthma adds another roughly $16.8 billion to this total economic impact

This amount is truly astronomical, though as a disclaimer, it is an estimate of the costs. The main source of this cost is in the healthcare expenses related to mold, revealing it as a huge public health issue.

Mold also affects physical property, damaging wood and insulation, and incurring damage costs if mold growth is too widespread. It is also a social issue—people who live in homes with mold may struggle with the stigma of having mold, and might struggle with the stress of the situation.

Mold-related deaths are attributable to around 30% of asthma deaths worldwide, which adds grief and mortality as major stressors, adding to the severity of the situation. Many people are very afraid of getting mold in their homes, for these exact reasons.

Find Mold Removal Professionals Near You

Mold growth in your home can be devastating to your health. There are many lung diseases that are either caused by or made worse by mold. Mold problems are very common, but also preventable. The best way to help your health and reduce your health risks is to treat mold before it grows and solve the problem as soon as you see it.

Water damage is a leading cause of indoor mold growth. Professional mold remediation services can help reduce mold’s impacts on your home and your health.

Home remedies like dehumidifiers and cleaning with bleach solutions in bathrooms can help treat early infections. Checking on water leaks and indoor dampness can help you see the signs of mold before a serious problem takes hold. Mold experts can help diagnose and treat mold problems as soon as you see them.

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The Water Damage Advisor content team is made up of multiple contributors, writers, and editors. We are your resource hub for anything related to water damage, mold and restoration needs that you may be challenged with facing.

9 References
  1. WHO. (2009). WHO guidelines for indoor air quality: dampness and mold.
  2. Real Time Laboratories. Mold Statistics and Facts.
  3. WHO. (2016). Preventing Disease Through Healthy Environments.
  4. CDC. (2020). CDC - Basic Facts about Mold and Dampness.
  5. Environmental Health Perspectives. (2007). A Spreading Concern: Inhalational Health Effects of Mold.
  6. EPA. Mold and Health.
  7. Science Daily. (1999). Mayo Clinic Study Implicates Fungus As Cause Of Chronic Sinusitis.
  8. American Lung Association. (2020). Aspergillosis.
  9. Hindawi Publishing Corporation. (2016). Valuing the Economic Costs of Allergic Rhinitis, Acute Bronchitis, and Asthma from Exposure to Indoor Dampness and Mold in the US.
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