How does Dew Point Influence Indoor Air Quality and the production of Allergens?

Overview: Dew Point affects indoor air quality and allergen production. High humidity levels can create a conducive environment for allergens like mould, dust mites, and bacteria to thrive, worsening indoor air quality and potentially triggering allergic reactions. Conversely, maintaining optimal indoor humidity levels can help mitigate allergen proliferation and improve overall air quality.

Dew Point is a critical factor in the proliferation of microorganisms, but how does it influence Indoor Air Quality and the production of Allergens?


Intro to Microorganisms

Microorganisms are tiny organisms that are invisible to the naked eye and can only be seen under a microscope. They are found everywhere in the environment, including in the air, water, soil, and even inside our bodies. While these three groups of microorganisms are all very different, they share some common characteristics.

They are all:

  • Microscopic: They are too small to be seen with the naked eye.
  • Unicellular: They comprise only one cell (except for some types of mould).
  • Prokaryotic (bacteria) or eukaryotic (mould and viruses) have different internal structures.
  • Rapidly reproducing: They can reproduce quickly under the right conditions.

Allergens: Defined by nature and potential impact Immunoglobulin E (IgE)-mediated: These allergens trigger immediate allergic reactions involving IgE antibodies, causing symptoms like hay fever, asthma, and anaphylaxis.

Non-IgE-mediated: These allergens cause delayed allergic reactions not involving IgE, such as food intolerances, eczema, and contact dermatitis.

Dew Point is a critical factor impacting microorganisms.

Maintaining dew points below 55°F (13°C) is a crucial step in promoting good IAQ and preventing potentially harmful microbial growth.

Dew point plays a crucial role in indoor air quality (IAQ) as it directly influences the risk of mould and bacteria growth. Understanding the problematic thresholds helps us manage humidity effectively and maintain a healthy indoor environment.


Dew Point Explained:

The dew point is the temperature at which air becomes saturated with water vapour, causing condensation to form on surfaces. Higher temperatures can hold more moisture, so the higher the dew point, the more humid the air feels.


Relationship with Humidity:

  • Humidity refers to the amount of water vapour in the air. Higher humidity indicates more water vapour present.
  • Dew point directly influences relative humidity (RH). For example, at a constant temperature, the higher the dew point, the higher the RH (and vice versa).

ABOVE Relative Humidity (RH), demonstrated by the amount of moisture present in the air relative to the current maximum moisture capacity of that air as it varies depending on the air temperature. Credit shutterstock / Dimitrios Karamitros

Importance of Dew Point:

  • Understanding weather: Dew point plays a crucial role in predicting weather phenomena like fog, cloud formation, and precipitation. When the dew point is close to the air temperature, these conditions become more likely.
  • Assessing comfort: Dew point impacts how comfortable we feel. High dew points in warm weather can make us feel sticky and uncomfortable, while low dew points in cold weather can lead to dry skin and respiratory irritation.
  • IAQ and mould growth: In indoor environments, dew point influences the risk of mould growth. High dew points combined with warm temperatures and organic matter create ideal conditions for mould to thrive.

ABOVE Real world example of moisture accumulation, as result of Dew Point parameters. Source: Clean-Air Aust

Measuring Dew Point:

Dew point can be measured directly using specialised instruments or calculated from temperature and humidity readings. Many weather stations and even some home weather stations measure dew point.

Tips for Living with Dew Point:

  • Monitor dew point and adjust climate control settings: Depending on your desired comfort level, you can adjust air conditioning or dehumidifiers to manage humidity and keep the dew point within a comfortable range.
  • Be mindful of indoor moisture sources: Activities like showering, cooking, and using washing machines can increase indoor humidity. Proper ventilation and moisture control are crucial to prevent mould growth and maintain a healthy indoor environment.

Understanding dew point and its connection to humidity can empower you to make informed decisions about weather, comfort, and even indoor air quality in your surroundings.

It's not just about feeling chilly when the air is "damp" – dew point plays a significant role in various aspects of our lives.


The Problematic Dew Point Range for Mould and Bacteria

For mould and bacteria growth, ideal conditions involve both sufficient moisture and organic material (food source). While specific requirements vary across species, generally, dew points above 55°F (13°C) significantly increase the risk of mould and bacteria proliferation.


Why is High Dew Point Problematic?

  • Condensation: High dew point encourages condensation on surfaces like walls, ceilings, and furniture, creating ideal breeding grounds for mould and bacteria.
  • Increased humidity: High humidity provides a favourable environment for mould spores and bacteria cells to thrive and reproduce.
  • Dust mite activity: Dust mites, a common allergen source, also flourish in humid environments, exacerbating respiratory issues.


How to Manage Dew Point for Optimal IAQ?

  1. Maintain humidity levels below 55%: Using dehumidifiers, air conditioning, or proper ventilation can effectively control humidity and keep dew points below the critical threshold.
  2. Address moisture sources: Identify and address sources of excess moisture like leaks, poor ventilation, or wet basements.
  3. Regular cleaning and maintenance: Regularly clean mould-prone areas and maintain proper ventilation to prevent mould growth.
  4. Monitor dew point: Invest in hygrometers to monitor indoor humidity levels and take timely action when dew points rise.


Additional Dew Point Considerations:

  • Building materials: Porous materials like wood and drywall are more susceptible to mould growth at high dew points.
  • Occupancy and activity levels: Higher occupancy and activity levels generate more moisture, necessitating stricter humidity control.
  • Regional climate: Local climate and seasonal variations influence ideal dew point levels.

By understanding the relationship between dew point and mould/bacterial growth, we can effectively manage indoor humidity and create a healthy and comfortable living or working environment.

Maintaining dew points below 55°F (13°C) is a crucial step in promoting good IAQ and preventing potentially harmful microbial growth.


How to Classify Microorganisms; Mould, Bacteria, and Viruses

Invisible to the naked eye, microorganisms can only be seen under a microscope. They are found everywhere in the environment, including in the air, water, soil, and even inside our bodies.Here are some classifications they fall into:

[1] Indoor mould growth


A type of fungus that grows in damp or humid environments. It can cause allergies and respiratory problems.

[2] Anatomy of Bacteria


Single-celled organisms that can be both beneficial and harmful. Some bacteria help us digest food and produce vitamins, while others can cause infections.

[3] SARS-CoV-2, a member of the subfamily Coronavirinae


Even smaller than bacteria and are not considered living organisms. They can only reproduce inside the cells of other organisms, such as plants and animals. Viruses can cause a variety of diseases, including the common cold, flu, and AIDS.

While these three groups of microorganisms are all very different, they share some common characteristics. They are all:

  • Microscopic: They are too small to be seen with the naked eye.
  • Unicellular: They are made up of only one cell (except for some types of mould).
  • Prokaryotic (bacteria) or eukaryotic (mould and viruses): They have different internal structures.
  • Rapidly reproducing: They can reproduce quickly under the right conditions.

Microorganisms play an important role in the environment and in our lives. They are essential for decomposing organic matter, recycling nutrients, and producing some of the foods and medicines we rely on. However, some microorganisms can also cause disease. It is important to be aware of the risks associated with microorganisms and to take steps to protect ourselves from them.


How does Dew Point influence Microbial Allergen Production, Propagation, and Growth?

The relationship between dew point and microbial allergens is complex and multifaceted. While dew point itself doesn't directly cause allergies, it can indirectly influence the production, propagation, and growth of microorganisms that trigger allergic reactions, such as:

Mould and Fungal Allergens:

High dew points (above 55°F or 13°C) combined with warm temperatures and organic matter create ideal conditions for mould growth.

Mould spores release allergens that can trigger allergic reactions in sensitised individuals, causing symptoms like sneezing, runny nose, itchy eyes, and even asthma attacks.

[4] Mould growth on a damp wall

Dew point can also influence the release and dispersal of mould spores. Higher humidity levels can help keep spores airborne for longer periods, increasing the risk of exposure and allergic reactions.


Dust Mite Allergens:

Dust mites are tiny creatures that thrive in warm, humid environments. Moderate dew points (around 50-60% relative humidity) provide optimal conditions for dust mite reproduction and allergen production.

Dust mite allergens can trigger allergic reactions similar to those caused by mould, including respiratory symptoms and skin irritation.

[5] Dust mites under the microscope


Cockroach Allergens:

Cockroaches are another common source of indoor allergens. While not directly impacted by dew points, they are more likely to thrive in warm, humid environments, which often coincide with higher dew points.

Cockroach allergens can trigger allergic reactions, especially in children and individuals with asthma.


Overall consideration

  • High dew points, in combination with other factors like warm temperatures and organic matter, can create favourable conditions for the growth of mould and other allergen-producing microorganisms.
  • Moderate dew points may also contribute to the proliferation of dust mites and cockroaches, further increasing allergen levels in indoor environments.

It's important to note that dew point is just one factor among many that can influence microbial allergen levels. Other factors like ventilation, indoor temperature, the presence of organic matter, and cleaning practices also play a significant role.

Here are some tips for managing indoor allergens and minimising the potential impact of dew point:

  • Maintain Good Ventilation: This helps to remove moisture and allergens from the air.
  • Control Indoor Humidity: Aim for a relative humidity level between 30-50%. You can use a dehumidifier to help achieve this.
  • Regular Scheduled Cleaning: This includes vacuuming, dusting, and washing bedding and curtains.
  • Address Mould and Moisture Problems Promptly: Don't let mould grow in your built environment. If you see mould, remove it immediately and address the underlying moisture issue.
  • Consider Using Air Purifiers: Air purifiers with HEPA filters can help to remove allergens from the air.

By taking these steps, you can help to create a healthier indoor environment and reduce your exposure to microbial allergens.


Our Understanding of allergens

An allergen is a substance that triggers an abnormal immune response in some individuals, leading to an allergic reaction. These reactions range in severity from mild discomfort to life-threatening emergencies.

ABOVE Common Allergens Related to Indoor Air Quality

Here's a deeper dive into the concept:

Immune System Recognition:

  • The immune system's primary function is to protect the body from harmful invaders like bacteria and viruses.
  • In individuals with allergies, the immune system mistakenly identifies certain harmless substances (allergens) as threats.


  • Upon initial exposure to an allergen, the immune system produces specialised antibodies called Immunoglobulin E (IgE).
  • These IgE antibodies attach to mast cells and basophils, immune cells present in tissues like the skin, lungs, and nose.

Re-exposure and Activation:

  • Subsequent exposure to the same allergen triggers the IgE-coated mast cells and basophils to release a cascade of chemical mediators like histamine, leukotrienes, and prostaglandins.

Inflammation and Symptoms:

  • These mediators induce inflammation in the affected tissues, resulting in the characteristic symptoms of an allergic reaction:
    • Runny nose, sneezing, and itchy eyes in case of hay fever.
    • Wheezing, coughing, and shortness of breath in asthma.
    • Hives, itching, and skin irritation in eczema.
    • In severe cases, anaphylaxis, a life-threatening reaction requiring immediate medical attention.

Types of Allergens:

  • Biological: Pollen, dust mites, mould spores, pet dander, insect venom.
  • Food: Peanuts, shellfish, dairy, soy, eggs.
  • Chemical: Latex, medications, formaldehyde, some industrial chemicals.

Factors Influencing Allergic Reactions:

  • Genetics: Some individuals are genetically predisposed to produce higher levels of IgE, making them more prone to allergies.
  • Exposure: The frequency and amount of allergen exposure can impact reaction severity.
  • Environmental factors: Temperature, humidity, and pollution levels can influence allergen levels and susceptibility.

Managing Allergens:

  • Avoidance: Identifying and minimising exposure to trigger allergens is key.
  • Medication: Antihistamines, corticosteroids, and other medications can help manage symptoms.
  • Immunotherapy: For some allergies, specific immunotherapy can retrain the immune system to tolerate the allergen.

In conclusion, allergens are seemingly harmless substances that, for some individuals, trigger an exaggerated immune response resulting in allergic reactions. Understanding what allergens are, how they interact with the immune system, and the available management strategies are crucial for individuals with allergies to lead healthy and comfortable lives.


How do Allergens Function?


Immunoglobulin E (IgE): The Gatekeeper of Allergic Reactions

Immunoglobulin E (IgE) is a type of antibody, a protein produced by the immune system, that plays a key role in allergic reactions. Unlike other antibodies, IgE targets specific allergens – harmless substances like pollen, dust mites, or food proteins – that some people's immune systems mistakenly identify as threats.

Here's a breakdown of IgE's role in allergic reactions:

  1. Sensitization:
  • When an allergen is encountered for the first time, IgE production is minimal.
  • The immune system creates specialised IgE antibodies specific to that allergen and remembers them.
  1. Re-exposure:
  • Upon subsequent exposure to the same allergen, IgE antibodies quickly bind to the allergen on mast cells and basophils – immune cells present in tissues like the skin, lungs, and nose.
  1. Activation:
  • This binding triggers the mast cells and basophils to release a cascade of chemical mediators, including histamine, leukotrienes, and prostaglandins.
  1. Inflammation:
  • These mediators cause inflammation and the characteristic symptoms of an allergic reaction, like runny nose, itchy eyes, wheezing, or even anaphylaxis in severe cases.

Key Characteristics of IgE:

  • High Affinity for Allergens: IgE binds tightly to allergens, ensuring a strong activation signal for mast cells and basophils.
  • Short Half-Life: IgE antibodies circulate in the bloodstream for only a few days, contributing to the transient nature of most allergic reactions.
  • Genetic Influence: Some people are genetically predisposed to produce higher levels of IgE, making them more prone to allergies.

IgE: Beyond Allergies:

  • While best known for its role in allergies, IgE also plays a part in some parasitic infections and contributes to defence against certain toxins.

Understanding IgE can help us:

  • Develop allergy diagnostics and treatments: Measuring IgE levels specific to certain allergens can help diagnose allergies. Antihistamines and other medications target the mediators released by activated mast cells and basophils to alleviate symptoms.
  • Develop strategies for allergy prevention: Early exposure to certain allergens in controlled settings can sometimes train the immune system to tolerate them in the future.

While IgE can be a troublemaker in cases of allergy, it's an important component of our immune system's diverse repertoire. Understanding its function helps us manage allergies and appreciate the intricate workings of our body's defence mechanisms.


Managing Dew Point Helps us Provide Safe Indoor Environments

This understanding of Dew Point not only widens our knowledge but also helps manage its impact on Indoor Air Quality and Allergen Proliferation in closed spaces, in a further effort to raise awareness and provide solutions for safer, healthy indoor environments.


Safe indoor air from a serviced HVAC system means a lower particle count and less breathing difficulties for occupants of the building. Clean-Air are IICRC mould remediation experts with the knowledge and experience to test, treat and eliminate serious mould-related risks within your HVAC system. If you have concerns about the air you are breathing, or would like an HVAC health check, contact our team today.


Sources and Additional Resources on Dew Point, Microorganisms, and Scientific Articles and Resources:

The American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) Standard 55-2020, Thermal Environmental Conditions for Human Occupancy: This standard provides guidance on temperature, humidity, and airflow recommendations for optimal thermal comfort and health in built environments.

The Environmental Protection Agency (EPA) guide on mold and moisture: This guide offers information on mold growth conditions, health risks, and strategies for prevention and remediation.

"Dew Point and Humidity: Their Role in Mold and Dust Mite Growth" by the National Pest Management Association (NPMA): This article delves into the specific influence of dew point on these allergen-producing microorganisms.

"Indoor Allergens and Human Health: A Review" by the International Journal of Environmental Research and Public Health: This research paper provides a comprehensive overview of various indoor allergens and their impact on health.

Websites and Organisations:

The Indoor Air Quality (IAQ) Division of the EPA: This website provides resources and information on various IAQ concerns, including indoor allergens and humidity management.

The American Lung Association: This organization offers educational materials and resources on respiratory health, including information on allergies and asthma triggered by indoor air quality factors.

The National Institute of Environmental Health Sciences (NIEHS): This institute provides research and resources on environmental factors impacting health, including indoor air quality and its link to allergic diseases.

[1] Mould [2] Bacteria [3] Viruses [4] Mould and Fungal Allergens [5] Dust Mites