Allergy Facts, Symptoms, and Treatment

Mold (aka mildew, mould) is a type of fungus found both indoors and out.1,2,3 Mold reproduces via spores, which can be transported by air, water, and insects.4,5 After inhaling these spores, those allergic to mold may experience symptoms.6 While most reactions occur from mid-summer to early fall, some molds can survive a killing frost, and a few species can grow at subfreezing temperatures.5,7 Although snow cover may lower mold counts, it doesn t actually kill most species, and after a spring thaw, surviving mold will thrive on vegetation killed by winter cold.7

Of the more than 1 million fungal species, roughly 80 have been linked to respiratory allergy.8 Along with causing symptoms of allergic rhinitis (aka hay fever) mold allergy is also a major risk factor for developing upper and lower respiratory diseases such as asthma.6,8 The molds most likely to cause allergy symptoms are Alternaria alternata, Cladosporium herbarum, Aspergillus fumigatus, and Penicillium.8 Mold sensitization is found around the world and is estimated to affect 3 to 10 percent of the population.9 However, in those with asthma, prevalence estimates can be as high as 80 percent.10

Where is mold found?

While molds grow best in warm, wet, and humid conditions, they can survive almost anywhere there is sufficient moisture and nutrients.2,8 Most species prefer temperatures of 15 to 30 C (59 to 86 F), but some can grow in temps of 35 to 50 C (95 to 122 F).2 Outdoors, this type of fungus can live in or on a plethora of mediums, including soil, dust, rotting logs, fallen leaves, compost, grasses, and weeds. Some species can also invade various crops, such as wheat, oats, barley, and corn, and may be found in some spices and marijuana.7,12

Indoor mold prevalence in cold climates is between 5 and 10 percent, but those figures jump to 10 to 30 percent in warm climates.8 In addition to colonizing in residential dwellings, mold can also thrive in bakeries, breweries, barns, dairies, and greenhouses.7 Within homes, the fungus can be found in damp locales such as basements and bathrooms, where it grows on myriad surfaces including shower doors, refrigerator drip trays, house plants, air conditioners, humidifiers, garbage cans, carpets, ceiling tiles, insulation, wood, paint, drywall, mattresses, upholstered furniture, and pillows.2,7 Plus, mold can colonize food, invading both the surface and its interior. That is, if a food shows heavy mold growth on the top, additional mold roots (i.e., very thin, perhaps invisible, threads) may have deeply penetrated below the surface.4

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Are there other allergens I could be sensitized to?*

Some people with a mold allergy may also experience symptoms when exposed to other types of mold. This is called cross-reactivity and occurs when your body's immune system identifies the proteins, or components, in different substances as being structurally similar or biologically related, thus triggering a response.13

*These products may not be approved for clinical use in your country. Please work with your healthcare provider to understand availability.

How do I manage my allergy?

If you are allergic to mold, your healthcare provider may recommend a plan that includes the following.5,6,14,15,16

  • Limit your outdoor time during seasons when mold is most active.
  • Wear a mask when disturbing or moving plant materials, and avoid raking and burning dry leaves.
  • Avoid barns, silos, hay, straw, and peat moss.
  • Use a certified asthma and allergy friendly filter attachment on your heating and air conditioning unit, and change filters regularly.
  • Employ dehumidifiers to lower indoor humidity levels to less than 45 percent to create an environment where mold is less likely to thrive.
  • Improve air flow through rooms by opening doors between spaces, moving furniture away from the walls, and operating fans.
  • Use exhaust fans in bathrooms and kitchens to pull moisture out of the rooms.
  • Fix any plumbing leaks, check windows for condensation, and remove sources of dampness.
  • Repair roof leaks, clean gutters, and ensure rainwater drains away from your dwelling.
  • Clean thoroughly and regularly, including sinks and tubs, refrigerator door gaskets, and garbage cans.
  • Remove clothes from washing machines promptly and clean rubber seals regularly.
  • Eliminate sources of dampness in basements, such as pipe leaks and groundwater seepage.
  • Run ventilation fans during and after showers and baths.
  • Remove any carpet from bathrooms and basements.

Your healthcare provider may direct you to employ one of the following therapies to improve your allergy symptoms:

  • Antihistamines are commonly used to reduce symptoms such as sneezing, itching, and runny nose.
  • Nasal corticosteroids are used to reduce swelling in the nose and block allergic reactions.
  • Oral and nasal spray decongestants can be employed to relieve stuffiness.
  • Daily nasal lavage using a squeeze bottle filled with salt water can help clean out irritants and alleviate nasal symptoms.
  • Anti-inflammatories, such as montelukast, can be effective in treating mold allergy. 
  • Allergen immunotherapy, as directed by your healthcare provider, may help develop tolerance to mold exposure.

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Common Symptoms

Mold allergy symptoms can range from mild to severe and vary person to person.6 Reactions can happen almost immediately after exposure, or they can be delayed. Symptoms are most common in mid-summer to early fall, but since molds grow both indoors and out, allergic reactions can occur all year.5

Symptoms typically include one or more of the following:6,11

  • Nasal congestion
  • Runny nose
  • Sneezing
  • Irritated, watery eyes
  • Coughing
  • Wheezing
  • Itchy eyes, nose, and throat
  • Dry, scaly skin

Mold sensitization is also a major risk factor for developing upper and lower respiratory diseases such as allergic rhinitis (aka hay fever) and asthma.8 In addition, other reactions can include:6,7

  • Allergic fungal sinusitis (an inflammation in the sinuses)
  • Allergic bronchopulmonary aspergillosis (a lung disease whose symptoms may include wheezing, low-grade fever, and coughing up brown-flecked masses or mucus)
  • Hypersensitivity pneumonitis (a rare condition that causes lung inflammation)

A small percentage of asthmatics with inhaled mold allergy can also develop allergic urticaria (aka hives) when they eat or drink anything containing yeast or mold.1 In addition to causing allergic reactions, molds can also lead to infections along with toxic reactions.2


How do I know if I'm allergic?*

Together with your symptom history, skin-prick testing or specific IgE blood testing can help determine if you are allergic to a particular allergen. If you are diagnosed with an allergy, your healthcare provider will work with you to create a management plan.

*These products may not be approved for clinical use in your country. Please work with your healthcare provider to understand availability.

Is there a risk for a severe event?

Exposure and sensitization to fungal allergens can promote the development and worsening of allergic diseases such as allergic rhinitis and asthma.13

  1. GI Society [Internet]. Vancouver, BC, Canada: Canadian Society of Intestinal Research; 2004 Mar/Apr. Available from:
  2. Storey E. Guidance for clinicians on the recognition and management of health effects related to mold exposure and moisture indoors. Farmington, CT: University of Connecticut Health Center, Division of Occupational and Environmental Medicine, Center for Indoor Environments and Health; 2004.
  3. Centers for Disease Control and Prevention [Internet]. Atlanta, GA: National Center for Environmental Health; 2020 Aug 11. Available from:
  4. United States Department of Agriculture [Internet]. [place unknown]: United States Department of Agriculture; 2013 Aug. Available from:,that%20can%20make%20you%20sick.
  5. Asthma and Allergy Foundation of America [Internet]. Arlington, VA: Asthma and Allergy Foundation of America; 2015 Oct. Available from:
  6. Mayo Clinic [Internet]. Rochester, MN: Mayo Foundation for Medical Education and Research; 2019 Apr 3. Available from:
  7. PennState Hershey, Milton S. Hershey Medical Center [Internet]. Bethesda, MD: National Institutes of Health; 2012 Jun 29. Available from:
  8. Ozdemir O (2015) Molds and Respiratory Allergy - Part 1. MOJ Immunol 2(2): 00045. DOI: 10.15406/moji.2015.02.00045. Available from:
  9. Twaroch TE, Curin M, Valenta R, Swoboda I. Mold allergens in respiratory allergy: from structure to therapy. Allergy Asthma Immunol Res. 2015 May;7(3):205-20. doi: 10.4168/aair.2015.7.3.205. Epub 2015 Mar 11. PMID: 25840710; PMCID: PMC4397360. Available from:
  10. Simon-Nobbe B, Denk U, Pöll V, Rid R, Breitenbach M. The spectrum of fungal allergy. Int Arch Allergy Immunol. 2008;145(1):58-86. doi: 10.1159/000107578. Epub 2007 Aug 20. PMID: 17709917. Available from:
  11. American College of Allergy, Asthma & Immunology [Internet]. Arlington Heights, IL: American College of Allergy, Asthma & Immunology; 2018 Apr 23. Available from:
  12. American Thoracic – American Thoracic Society [Internet]. New York, NY: American Thoracic Society. 2018. Available from:
  13. Fukutomi, Yuma & Taniguchi, Masami. (2015). Sensitization to fungal allergens: Resolved and unresolved issue. Allergology International. 145. 10.1016/j.alit.2015.05.007. Available from:
  14. Mayo Clinic [Internet]. Rochester, MN: Mayo Foundation for Medical Education and Research; 2019 Apr 3. Available from:
  15. Nationwide Children’s Hospital [Internet]. Columbus, OH: Nationwide Children’s Hospital; 1976 [2018 Oct]. Available from:
  16. Bozek A, Pyrkosz K. Immunotherapy of mold allergy: A review. Hum Vaccin Immunother. 2017 Oct 3;13(10):2397-2401. doi: 10.1080/21645515.2017.1314404. Epub 2017 May 8. PMID: 28481693; PMCID: PMC5647975.