Mold and Mildew – Causes, Signs and symptoms

Mold and Mildew


Mold and mildew are fungi or primitive plants that can be found both indoors and outdoors. Molds thrive in warm, damp and humid conditions but can survive in

freezing environments. Molds reproduce by releasing spores or seeds which are easily spread by wind or circulated by air-conditioning. Mold can grow wherever moisture is present. The bathroom, kitchen and basement are ideal environments for mold to grow. The terms mold and mildew mean virtually the same thing but mildew generally refers to a mold infestation that is visible.

Allergic reactions to mold and mildew are common and can occur year-round. People sensitive to molds can experience symptoms such as skin irritation, nasal congestion, eye irritation and wheezing. Severe allergic reactions to mold may include fever and shortness of breath. Mold may also cause asthma or other respiratory ailments. People who are allergic to other airborne allergens (e.g., pollen, dander, dust and dust mites) may be more susceptible to mold allergies.

Mold allergies can be diagnosed by a physician. As with all allergies, mold allergies cannot be cured. The best treatment strategy for mold allergies is avoidance.

There are many ways to reduce the presence of molds indoors and limit exposure to them outdoors. However, completely eliminating molds from indoor environments is not possible. Microscopic mold spores are constantly present in virtually all environments. Therefore, allergy medications may be recommended to help control symptoms. In persistent or severe cases, allergy shots (immunotherapy) may be necessary.

About mold and mildew

Mold and mildew are microscopic fungi that feed on organic material such as plant or animal matter. Mold and mildew are identical except mildew usually refers to mold that can be seen (e.g., spores, fuzzy growth, discoloration). Not all mold is visible. 

There may be over 100,000 mold varieties that survive both outdoors and indoors by spreading spores (tiny reproductive cells). Mold spores spread easily through the air. When spores are inhaled they can cause allergic rhinitis (hay fever). Because of their size, they can also reach the lungs. These airborne spores can produce mild to severe symptoms in people who are sensitive to these allergens. Allergies to mold are also responsible for a large number of severe asthmatic conditions.

Mold and mildew allergies are usually triggered by inhaling mold spores into the lungs but may also be triggered by contact with the skin, mouth, nose and eyes. Eating foods contaminated with mold or mildew may also trigger an allergic reaction and may affect the digestive system.

Molds play a vital role in nature by decomposing leaves, wood and animal matter. Some molds are cultivated for food and medicine. Cheese and penicillin, for example, are produced by specific molds in controlled environments.

Mold can be odorless or have a musty odor or earthy smell – particularly with large mold or mildew infestations. Some molds cannot be seen because the infestation is small. When it is visible, mold commonly has a black or greenish color. Mold and mildew can be any color, however, including brown, orange, yellow, violet, blue and white.   

Unlike other airborne allergens, such as pollen, mold does not have a specific season. Instead, mold concentrations are affected by weather conditions such as wind, humidity, rain and temperature.

Mold and mildew can survive outside in freezing temperatures to eventually thrive again in warmer weather. Outdoor mold spores generally begin to appear in the spring, with levels peaking in July in warmer areas of the country and October in colder areas. Mold spores can be found outdoors year-round in many states, particularly those in the South and on the West coast. Mold can be found indoors throughout the year.

Mold allergies commonly develop in patients who are allergic to other airborne allergens, such as animal dander and pollen. The condition is also common in those who have relatives with airborne allergies. People with certain occupations are also at an increased risk for developing mold allergies due to a high level of exposure to mold. Those at risk include:

  • Farmers
  • Dairymen
  • Loggers
  • Bakers
  • Mill workers
  • Carpenters
  • Greenhouse employees
  • Wine makers
  • Furniture repairers

Toxic mold (or black mold) refers to large accumulations of mold that are hidden or concealed. This mold is usually Stachybotrys chartum (Stachybotrys atra) but can also be other forms of mold. It may grow in areas that cannot be easily detected, such as in air ducts, remote basement or attic spaces, or in the hollow spaces of walls. 

Many experts link this type of mold infestation with extreme allergic reactions, birth defects, miscarriages, lung diseases, respiratory illnesses, various infections, cancer, memory loss, brain damage and death (a possibility for infants, elderly and people who are already ill). However, other experts doubt the existence of toxic mold syndrome (illnesses caused by exposure to mold). 

Research into the effects of toxic mold is ongoing and how this type of mold affects the body is not completely understood. For instance, it is not known if all reactions to toxic mold are allergy related or if there is another body response involved. However, a recent study suggests that mold growing in homes is much more likely to trigger an allergic reaction than a toxic one. Patients are encouraged to discuss their concerns with a physician.

People with allergies to mold will need to limit their exposure to these allergens as much as possible. Pollen and mold counts may be helpful. Many news sources in major cities count mold spores by taking a sample of particulates in the air and then counting and identifying the specific mold spores in the sample. Depending upon the weather, however, the amount of airborne spores in the air can change rapidly. Counts may also differ between day and night. In addition, the specific mold that causes a person’s allergic reactions may not be counted separately. As a result, a mold count may not relate directly to the person’s condition. Knowing the general count, however, can help a person decide whether to stay indoors or not.

Diagnosing and treating mold and mildew allergies involve the same methods as most other allergies. A physician will conduct a physical examination and obtain the patient’s medical history. If a mold allergy is suspected, the physician will perform an allergy skin test or blood test.

Once diagnosed, the best treatment strategy for mold and mildew allergies is avoidance. However, this is not always possible. Therefore, allergy medications, such as antihistamines, decongestants and corticosteroid nasal sprays, may be prescribed to help treat symptoms. Physicians may also recommend allergy shots (immunotherapy) for persistent or severe symptoms. This type of therapy works by regularly exposing an individual to very small amounts of mold allergen through a series of injections. By increasing their exposure to the allergen over a period of months or years, some individuals are able to build up a tolerance to the allergen. This can lessen the severity and frequency of allergic reactions in some people.

Potential causes of mold & mildew

Molds and mildew will grow wherever moisture and nutrients exist together. Outdoor mold can be found in shady or damp areas. Common places mold and mildew grow outdoors include:

  • Leaves and vegetation
  • Rotting logs, twigs and bark
  • Grasses, trees, bushes and flowers
  • Soil, sand, dirt and dust
  • Animal carcasses and feces
  • Hay, straw and feed
  • Compost heaps, mulch piles
  • Grains (e.g., wheat, oats, corn)
  • Construction areas

Mold spores ultimately enter a home or building from the outside through doorways, windows, heating ventilation and air-conditioning systems with outdoor air intakes. People and pets also carry mold spores in from the outside. Spores easily attach themselves to clothing, shoes, bags, hair and fur. Mold or mildew will grow when these spores fall in places where there is sufficient moisture and nutrients.

While there are hundreds of thousands of molds that thrive outdoors, fewer are found indoors. Common indoor molds include:

  • Alternaria (also common outdoors)
  • Aspergillus
  • Aureobasidium (Pullularia)
  • Bipolaris (also common outdoors)
  • Cladosporium (also common outdoors)
  • Epicoccum (also common outdoors)
  • Fusarium (also common outdoors)
  • Helminthosporium
  • Mucor
  • Penicillium
  • Rhizopus

Stachybotrys chartum (Stachybotrys atra) is less common, but not rare. This mold is most commonly associated with the terms “toxic mold” or “black mold,” although other forms of mold may also be called by these names.

Indoor mold can be found throughout a home or building in areas such as:

  • Bathrooms
  • Kitchens
  • Basements
  • Closets
  • Walls
  • Garages
  • Attics
  • Window moldings
  • Air–conditioning ducts
  • Storage areas
  • Laundry rooms
  • Crawl spaces
  • Garbage cans
  • Refrigerators
  • Barns
  • Greenhouses
  • Saunas
  • Houseplants

Because mold and mildew will grow where moisture exists, it can be found in every home or building in any climate. Water may accumulate within a home when ventilation is too poor to expel moisture produced by common activities like showering, cooking, washing clothes and cleaning.

Although molds thrive where water usage is common, high moisture levels can exist anywhere in a home as a result of water leaking from pipes, ducts, plant pots or appliances. Water may also enter a structure from the outside through the walls, floor or roof if the home or building is weak or damaged.

Flooding or poor drainage is a common cause of unwanted moisture in the home. Moisture in carpeting and upholstered furniture, for example, can produce mold (and allergens) in less than 48 hours because these materials have nutrients that encourage mold growth. Examples of other materials that may encourage mold growth when wet include:

  • Wood
  • Paper
  • Cardboard
  • Ceiling tiles  
  • Paints
  • Wallpapers
  • Insulation materials
  • Drywall
  • Fabric
  • Mattresses
  • Pillows
  • Window moldings

Related allergies and conditions

Mold and mildew spores are common allergens that affect many people in varying degrees. Individuals who have dust, dust mite, pollen, cockroach or animal dander allergies may be more susceptible to experiencing symptoms from mold exposure. Conditions closely linked to mold and mildew allergies include:

  • Allergic bronchopulmonary aspergillosis (ABPA). This is a condition which produces an immunologic response to the Aspergillus mold. ABPA has symptoms that are similar to asthma. Aspergillosis fungi (or other fungi) actually colonize the bronchial mucus. If ABPA is left untreated, however, an infection in the lungs can result, leading to permanent lung damage (fibrosis or bronchiectasis).

  • Aspergillus sinusitis. A condition caused by an Aspergillus allergy that affects the sinus cavity and head. Aspergillosis fungi (or other fungi) colonize the sinus cavity. It can cause headaches, congestion and discomfort in the face. For those with a weakened immune system, this type of allergy can lead to an infection. In this case the sinusitis is a form of invasive aspergillus that may cause more serious symptoms like a fever. Left untreated, an invasive aspergillus can lead to death. A diagnosis can be made in these instances by locating the aspergillus mold in fluid or sinus tissue or by other methods. 

  • Allergic rhinitis (hay fever). Inflammation of the inner lining of the nose that occurs when an allergic individual encounters an airborne allergen. Usually inhaled, these triggers generate allergy symptoms such as sneezing and runny nose.

  • Asthma. A chronic inflammation of the body’s bronchial tissues that afflicts millions of people in the United States. Mold allergies can trigger asthma attacks in some individuals. Mold exposure may also cause asthma. People with asthma experience shortness of breath, chest tightness, coughing and wheezing.

  • Allergic conjunctivitis. Inflammation of the clear membrane that covers the white of the eye (conjunctiva) as the result of an allergic reaction. It can result in itching, burning and redness of the eye, swollen eyelids, excessive tearing, eye discharge and other eye-related symptoms.

  • Allergic bronchitis. An allergic inflammation in the lower airway of the respiratory system. It is a type of asthma, an inflammatory condition of the airways. Allergic bronchitis is also linked with allergic rhinitis. This occurs through the nature of the respiratory system, which is a continuum from the nose to the lungs.

  • Sinusitis. Inflammation of the sinus cavities in the face caused by infection, allergies or irritants. Symptoms include runny nose, headache, dental sensitivity, nasal congestion and facial swelling.

  • Contact dermatitis. A skin reaction that occurs after direct skin contact with an allergen or irritant.

Individuals with certain health problems may experience more severe allergic reactions or their conditions may worsen when exposed to mold. Conditions of concern include:

  • Skin conditions (e.g., atopic dermatitis)

  • Chronic illnesses (e.g., COPD)

  • Weakened immune systems, as seen in infants, the elderly, HIV patients, chemotherapy patients and transplant recipients

Although cheese and yogurt are made with specific types of mold, there is no evidence that skin contact with or ingestion of these foods leads to an allergic reaction connected to mold and mildew allergies. However, milk allergy sufferers may be highly allergic to both yogurt and cheese.

Signs and symptoms of mold allergies

The symptoms produced by allergic reactions to mold and mildew depend on the nature of the allergic reaction triggered. For instance, allergens inhaled into the nose will produce symptoms associated with allergic rhinitis (e.g., sneezing, stuffy nose, runny nose, coughing). Allergens coming into direct contact with the eyes will produce eye-related symptoms associated with allergic conjunctivitis (e.g., itching, burning, redness). Skin rashes may also occur.

In people with asthma, exposure to mold can trigger asthma attacks. Signs and symptoms often associated with asthma attacks include wheezing, coughing and shortness of breath.

There can be a wide variation in how individuals react to mold exposure. People who may be affected more severely or quickly than others include:

  • Infants and children

  • Elderly people

  • Pregnant women

  • People with respiratory conditions, allergies or asthma

  • People with weakened immune systems (e.g., people with HIV infection, chemotherapy patients, organ or bone marrow transplant recipients, people with autoimmune diseases)

Some rare molds produce toxins called mycotoxins to defend against other molds and bacteria. The effects from inhaling mycotoxins are not clearly understood and are being studied, but some reports suggest that depending upon exposure level these mycotoxins may cause toxic effects in people. Some symptoms resulting from mycotoxin exposure include:

  • Fatigue
  • Nausea
  • Headaches
  • Respiratory irritation
  • Eye irritation
  • Inability to concentrate

Though unproven, some reports suggest that on extremely rare occasions toxigenic molds found inside homes may cause health conditions such as pulmonary hemorrhage or memory loss. Also largely unproven are reports that Stachybotrys atra or black mold can cause personality changes, sleep disorders and fatal bleeding in the lungs of infants when combined with secondhand smoke. People are encouraged to discuss their concerns over these or other symptoms and any potential link to mold allergies with their physician.

Tips for reducing mold and mildew

As with all allergies, mold allergies cannot be cured. However, there are steps people with mold allergies can take to avoid contact with mold and reduce the risk of allergy symptoms. There are both outdoor and indoor strategies that may significantly aid mold allergy sufferers.  

Tips for reducing mold contact when outdoors include:

  • Limit or avoid going to places that may contain mold.

  • Limit or avoid touching substances that may grow mold or mildew.

  • Avoid working outdoors when the published mold count is high. 

  • Avoid mowing grass (or being around freshly cut grass) and raking leaves, as these activities can stir up mold.

  • Avoid going outdoors after a rainstorm.

  • When working outdoors in areas likely to be damp or have mold (e.g., farms, construction sites), wear safety gear to limit exposure. This may include disposable dust masks, half-face respirators with charcoal cartridges, glasses or safety goggles, and rubber gloves. (NOTE: Latex gloves are also a potential allergen and should be avoided, if possible.)

Tips for cleaning or eliminating mold that has grown in a home or building include:

  • Hiring a professional service to clean the home of mold or mildew. The release of mold spores becomes intensified when moldy material is damaged or disturbed. People with mold allergies are not encouraged to complete the cleaning themselves, since it is likely to trigger symptoms. Also, anyone with asthma or respiratory problems should not be present when the cleaning takes place.  

  • Repairing any moisture leaks that are entering a home or building from the outside. Wear a dust mask and gloves and discard moldy or damaged materials.

  • Discarding any furnishings (e.g., mattresses, carpets, sofas) that were wet or have been stored in damp conditions.  

  • Scrubbing moldy areas with an unscented detergent solution (e.g., bleach), then sponging with a clean, wet rag and drying quickly (open windows or use fans to accelerate drying).  Unscented detergents are recommended because they make it easier to detect moldy odors that remain.

  • Cleaning moldy drywall using a damp rag with baking soda or some unscented detergent. Avoid wetting drywall too much when cleaning. If the mold returns after cleaning, it usually indicates that a source of moisture (e.g., leak from outside, sweating pipes) has not been removed.

  • Using a vacuum with a HEPA filter.

Tips for preventing mold in a home or building include:

  • Keeping windows closed. This can prevent molds from entering the home. Instead, use air conditioners to cool the home because they also clean and dry the air. Central air conditioning with a HEPA filter attachment is best.

  • Having family and friends remove shoes when entering a home. Shoes often have mold spores attached to them because of contact with soil, dust or dirt. Removing shoes at the door can reduce the spread of mold spores into the home.

  • Keeping the interior as dry as possible. Check the interior for signs of moisture and molds regularly.

  • Finding and fixing water leaks immediately.

  • Drying any wet or flooded areas in the home as quickly as possible. This will help prevent mold growth. Use a dry/wet vacuum or clean, dry rags to remove moisture on surface areas. Fans and open windows may be used to accelerate the drying. If wood flooring has remained wet for more than a day, a vacuum sander may be needed. Severely moldy flooring or carpet should be replaced.

  • Discarding clutter and excess stored materials – especially in basements, which tend to have more moisture. Molds grow on paper, fabrics, wood and anything else that holds moisture and collects dust. If you must store items like paper, clothes and fabric, do so in sealed containers.

  • Cleaning and maintaining the home or building regularly.

  • Using a dehumidifier to reduce moisture in the home during the warmer months. Dehumidifying a basement during the spring and summer, for instance, will help prevent the spread of molds. Windows should be closed when the dehumidifier is on. Raising the temperature in the basement can also help lower the humidity. The use of a humidifier should be avoided because these devices increase humidity levels.

  • Measuring how much moisture is present in the air of the home or building. To find the relative humidity in a home, a hygrometer is needed. Relative humidity in the home should be under 45 percent in the winter (or lower to avoid condensation on windows). A dehumidifier will help lower the relative humidity.  

  • Not using carpet in basements. This will help avoid the trapping of moisture.

  • Occasionally cleaning the drain in the basement floor by pouring in half a cup of bleach. Let it stand for a few minutes, then flush with water. Also, keep sump pits covered.

  • Cleaning heat recovery ventilators (HRV). If there is a HRV in the basement, clean the filter inside the HRV often.

  • Regularly cleaning and replacing furnace filters. Use a pleated 1-inch filter but not a coarse filter.

  • Venting laundry dryers to the outside only. Remove lint every time the dryer is used to help prevent moisture buildup. Also, dry washing machines after each use and avoid hanging clothes to dry indoors or outdoors.

  • Ensuring that bathrooms have a fan that exhausts to the outside. Turn the fan on when showering and leave on for several minutes after showering is completed to reduce moisture. Taking short showers will reduce mold as well. Wiping down wet surfaces after showering is also beneficial.

  • Consistently cleaning and drying walls and floors that are wet. Remove carpeting in the bathroom and clean rugs frequently. Check for water leaks under the sink, around the tub, shower and toilet to prevent water damage and mold or mildew. Clean and maintain drains in the bathroom to prevent extra moisture.

  • Ensuring that kitchen exhaust fans are vented to the outside and used regularly when cooking. Use a cover when boiling to prevent moisture buildup.

  • Maintaining sink drains and not allowing water to overflow the sink. Also, check under and around sinks for leaks and moisture buildup. Sinks and tubs should also be scrubbed at least once a month. 

  • Frequently cleaning the drip pan at the back of the refrigerator. Also vacuum dust from refrigerator coils.

  • Discarding old food from cabinets and refrigerators. Some moldy foods, however, such as cheeses, hard fruits and vegetables can be salvaged by cutting out a large area surrounding the mold.

  • Cleaning garbage cans frequently. Taking the garbage out daily will prevent mold and mildew growth as well.

  • Keeping closets and bedrooms clean and neat to make it easier for air to circulate and harder for mold to thrive. Throw out old clothes and other stored items that are not used.

  • Not bringing furniture, clothing, books or other items that have been water damaged or stored in a damp or moldy place into the home.

  • Reducing the number of potted plants in the home. Soil is an ideal place for mold to grow.

  • Increasing circulation throughout the home by using fans and opening doors and closets often.

  • Checking outside of the home (e.g., the roof and exterior walls) on a regular basis for any place water may enter. Eaves, troughs and downspouts should be checked often to make sure that they are connected, working properly and debris-free. Installing downspout extensions to lead water farther away from the home will also help in reducing potential interior water seepage.

Questions for your doctor on mold and mildew

Preparing questions in advance can help patients to have more meaningful discussions with their physicians. Patients may wish to ask their doctors the following questions about mold and mildew:

  1. Do my symptoms indicate a mold allergy?

  2. What methods will you use to determine if I am allergic to mold?

  3. What treatment options are available to me?

  4. In what places am I most likely to come into contact with mold?

  5. How can I reduce levels of mold in my home?

  6. How can I reduce my level of contact with mold when outdoors?

  7. Where can I find the daily mold levels for our area?

  8. Will my symptoms worsen at certain times of year or will they remain the same year-round?

  9. Does this condition pose a danger to my overall health?

  10. Should I be concerned about toxic mold syndrome?

  11. Would I benefit from the use of a dehumidifier?

  12. Are my children likely to develop mold allergies as well?
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