Mould Allergy Advice

Mould allergy explained

A mould allergy happens when the immune system mistakenly identifies microscopic fungal mould spores as harmful, triggering an allergic reaction. Mould spores can enter the human body by breathing (inhalation) mould in the environment, ingesting (being swallowed) mould on food contaminated with mould or via the skin (absorption) through a broken skin barrier due to conditions like eczema which can cause inflammation and itching.

Exposure to mould is widespread, and it is difficult to determine how much mould an individual is exposed to in everyday life. Like house dust mite allergy, mould allergy is perennial (all year round) and symptoms may be present throughout the year, although levels often rise in the autumn, during wet, mild weather and harvesting.

There are many different types of moulds and not all types cause allergy symptoms. Fungal spores, like pollen, are released seasonally, however, certain types are found in the air all year round, peaking in the summer months and then in late autumn. Indoor mould can be in the environment all year-round depending on the source.

Who can be affected by mould allergy?

Fungal spores are tiny (microscopic) and very fine, meaning they can be transported deep into the lungs and can be an allergic trigger for people who have respiratory forms of allergy, such as hay fever,  allergic rhinitis and asthma, as well as those with pre-existing long term respiratory conditions such as chronic obstructive pulmonary disease, cystic fibrosis, bronchiectasis and people with compromised immune systems.

Exposure to mould spores has the potential to affect people in different ways as mould can act as both an irritant and allergen, depending on the amount an individual is exposed to, the type of mould as well as the individual’s health, age, sensitivity and pre-existing health conditions.

Symptoms of mould allergy

• Runny or stuffy nose (nasal congestion)
• Sneezing and coughing
• Itchy, red, and/or watery eyes
• Wheezing, difficulty breathing, chest tightness
• Itchy throat or ears
• Postnasal drip.

Where is mould found?

Mould is present in both indoor and outdoor environments. Mould thrives in certain conditions including places that are dark, poorly ventilated and where there is excess moisture.

Outdoor mould grows in dark, damp places and is found under fallen leaves, in rotting vegetation, grass cuttings, compost heaps and garden sheds are all prime environments for mould growth.

The peak season for different types of mould differs in different parts of the country and over the seasons. The character and behaviour of spore’s changes with the season and local conditions. Mould counts are likely to change quickly, depending on the weather. Certain spore types reach peak levels in dry, breezy weather in summertime. Some need high humidity, fog or dew to release spores. This latter group is abundant at night and during rainy periods – typically during the autumn.

Monitoring of the fungal spore forecast can be done via the University of Worcester website.

Types of moulds

The moulds which are most associated with everyday modern living are found most of the year and in similar places. The most common moulds are as follows:

Penicillium Notatum – is widely distributed in soils and can also be isolated from decaying vegetables and leaves. It is found on stored cereals and hay. In a house, this mould is the green-blue mould found on stale bread, fruits and nuts and it is the mould that is used in the production of blue/green cheese types like Stilton. This mould is present all year round, however its concentrations reach a peak during winter and spring. This mould is associated with indoor allergy.

Cladosporium Herbarum – is the most frequently encountered mould in the air. Indoor concentrations of the spores reflect the outdoor concentration as this mould is easily transported through the air. Levels of this mould rise in the spring and peak in late summer and autumn. Cladosporium is one of the most common colonisers of dead plants and soil.

This is the mould that is frequently found on uncleaned refrigerators, food, window frames, straw, and houses with poor ventilation and in damp areas. This mould has also been isolated from fuel tanks, face creams, paints and textiles. It is the primary source of mould allergy.

Aspergillus Fumigatus – is found in soils, leaf and plant litter, decaying vegetables and roots, bird droppings, tobacco and stored sweet potatoes. Compared with other moulds, the concentration of spores in the air is relatively low. This mould is associated with asthma, also with bronchitis and conditions such as Farmer’s lung.

Alternaria Alternata – found in soils, food and textiles. The most common habitats for this mould are rotten wood, composts, bird’s nests and forest plants. Black spots on tomatoes and other foods are attributed to this mould. This is generally considered to be an outside mould and appears when conditions are warm.

Diagnosing a mould allergy

If you believe you or someone you care for has an allergy to mould, speak to your GP in the first place. They may need to ask a series of questions called an allergy-focused history to help identify potential allergens and/or allergies, gathering specific information on symptoms (onset, severity, triggers), personal/family history of atopic conditions (eczema, asthma, rhinitis) and environmental exposures.

If allergy testing is needed to help confirm a suspected diagnosis, this can be carried out depending on local availability and may require a referral to an allergy specialist/hospital for the testing to be performed. Allergy testing can be carried out by skin prick testing (SPT) where small drops of the different types of mould allergen extract are dropped onto the skin and a lancet used to prick the solution onto the skin. Another method is a Specific IgE blood test which can measure antibodies specific to mould that are present in the blood.

The link between mould allergy, perennial rhinitis and asthma

Airborne allergens like mould spores, once inhaled in susceptible individuals, may cause inflammation of the nose and sinuses, with symptoms such as a runny or congested nose, sneezing, and itchy and/or watery eyes. Exposure to indoor moulds commonly lead to symptoms that persist year-round, called perennial allergic rhinitis.

Asthma and mould allergy

For individuals with asthma and a mould allergy, breathing in mould spores can trigger an asthma flare-up, causing coughing, wheezing, chest tightness, and shortness of breath.

There is a strong link between mould exposure and the development and worsening of childhood asthma and allergic rhinitis especially in children. Mold spores are harmful to people with asthma. The small size of mould spores allows them to pass more easily into the lower airways, where they can trigger an asthma attack.

Several studies have identified rhinitis as a risk factor for asthma, with the prevalence of allergic rhinitis in asthmatic patients being 80% to 90%. When the upper airways (nose and sinuses) are inflamed due to rhinitis, it can negatively affect the lower airways (lungs), making asthma symptoms worse this link is often referred to as ‘one airway, one disease’.

It is also possible for mould spores to interact with other outdoor allergens such as pollen and air pollution increasing the allergenicity and posing a risk of more severe symptoms to individuals with allergic rhinitis and asthma.

Occupation and mould allergy

Mould can be an occupational allergen for those whose work involves spending prolonged period of times in mould-prone environments. Jobs with occupational mould exposure may include but are not limited to jobs in the following sectors:

• Building and Construction
• Farming and Conservation
• Cleaning and housekeeping
• Health and Social Care
• Food production
• Wood industry, logging and milling.

Mould exposure in the work environment can pose a significant health risk and should be reported to your employer without delay.

If you have a Health Condition where mould exposure acts as a trigger worsening symptom getting a review by a Health Care Professional and/or a referral to your Occupational Health Department if available is advised to ensure an accurate diagnosis and management plan.

Under the following laws if mould is present in the work environment a risk assessment and implementation of control measures will be required. Control of Substances Hazardous to Health (COSHH) Regulations 2022 and Health and Safety at Work Act 1974.

Indoor mould

Indoor mould is particularly relevant where the person spends large amounts of time indoors. The kitchen and bathrooms are often the hot spot areas of the home for mould. Indoor mould can grow on many different surfaces, including bathroom tiles, carpets, fabric and upholstery, wood, paint and wallpaper and in the soil of house plants.

Mould may be visible as black patches varying in size and location, however, it can also be hidden, for example, a leak in a roof can cause mould to grow in insulation, ceilings, floors or even on walls behind furniture. Mould is commonly found in damp places with poor ventilation including:

• Bathrooms
• Around window frames
• Behind wardrobes
• Under-sink cabinets
• Refrigerators
• Washing machines and clothes dryers
• Soft furnishings and wallpaper
• Indoor plants.

Practical tips for avoiding indoor moulds

Understanding the principles of what to avoid, when and where, is the key to managing your mould allergy.

• Moulds flourish in damp environments, therefore one of the best ways to prevent their growth is ventilation.
• Avoid damp basements, compost piles, fallen leaves, cut grass, barns and wooded areas, or wear a face mask if these places or things are unavoidable.
• Thorough cleaning of the kitchen, bathroom and utility room, with subsequent ventilation of these areas will help prevent mould growth. Pay attention to walls behind kitchen units and cupboards; the lack of ventilation often means that excess mould grows in these areas.
• Open windows and close internal doors when cooking, showering or bathing to prevent steam entering other rooms. Keep bathroom surfaces dry.
• When cooking, if possible, use extract fans and cooker hoods that are vented outside.
• Do not hang wet clothes inside or over radiators.
• Do not let food decay. Clean and thoroughly dry problem areas such as refrigerator seals.
• Clean mould from window frames and dry condensation.
• Do not hang clothes in damp cupboards or pack clothes too tightly in wardrobes. Leave wardrobe doors ajar to ventilate the clothes.
• Make sure that your tumble dryer is vented outside during use or use a condenser-dryer. Try not to dry damp clothing indoors.
• Replace old foam pillows and mattresses if possible.
• Do not bring in damp wood for the fire. Avoid burning wood inside that has been kept in a damp shed.
• Strip wallpaper from damp walls. Tackle any areas of dampness on walls etc.
• Remove piles of old newspapers.
• Keep houseplants to a minimum and change the soil regularly.
• Do not use humidifiers as this increase moisture that mould needs to thrive.
• If using a dehumidifier, the ideal indoor humidity is 50-55%. Empty and clean the reservoir regularly.

 Avoiding moulds outdoors

• Do not spend time in buildings where hay or grain is stored.
• Limit going into damp and musty buildings.
• Avoid cutting grass, raking leaves and turning compost heaps.
• Do not walk in the woods in mild damp conditions or among rotting leaves.
• Avoid country areas during harvesting, particularly when sunny and windy.
• Allergy bedding covers protect you from mould spores within the mattress, pillows and duvets.
• Filter facemasks, like those worn by cyclists, trap spores
• Mechanical ventilation systems can be effective at removing airborne allergens.

The Law around mould and living conditions

Awaab’s Law came into force in England in October 2025 (Hazards in Social Housing Regulations 2025) along with the Renters’ Rights Bill. These were developed following the tragic death in 2020 of Awaab Ishak, a two-year-old from Rochdale who died due to prolonged exposure to mould in his family’s social housing flat.

These two pieces of legislation place a legal duty on landlords to act swiftly when hazards such as damp and mould are identified. If an emergency hazard is suspected, landlords must investigate within 24 hours and complete any necessary safety work as soon as reasonably practicable.

Allergy UK has produced a Housing Rights Guide which contains useful information and practical advice on mould in the home that can be accessed here.