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Formaldehyde is highly volatile and gaseous at room temperature, and it is released into the air through off-gassing from various products inside the home. High humidity and temperatures can accelerate this process, leading to increased formaldehyde levels in indoor spaces. Formaldehyde is a known carcinogen.

Given the potential health risks associated with formaldehyde exposure, it is essential to maintain indoor levels of this chemical as low as possible, ideally below outdoor (background) levels. The average formaldehyde levels in homes of all types typically range between 24-56 parts per billion (ppb).

Common sources of formaldehyde indoors include products containing urea-formaldehyde (UF) resins and phenol-formaldehyde (PF) resins. Composite wood products like hardwood plywood, particleboard, and medium-density fibreboard, as well as pre-finished engineered flooring, building materials, insulation, glues, adhesives, paints, coatings, lacquers, finishes, textiles, disinfectant cleaning products, soaps, preservatives, some synthetic fabrics (permanent press), certain cosmetics, personal products (like certain hair sprays), and pet care products may also contribute to indoor formaldehyde levels. Additionally, combustion byproducts, such as tobacco smoke and emissions from fuel-burning appliances like gas stoves, kerosene space heaters, and fireplaces, can release formaldehyde into indoor air.

Volatile Organic Compounds (VOCs) are gases emitted from various solids or liquids and can include a range of chemicals, some of which may have negative health effects in both the short and long term. Interestingly, indoor concentrations of VOCs are consistently higher, sometimes up to ten times higher, than outdoor levels. VOC levels are often very high in new builds or renovations. VOCs can be found in a multitude of household products that we use daily. For instance, organic solvents are common ingredients in items like paints, varnishes, waxes, cleaning agents, disinfectants, cosmetics, and hobby products. Even fuels contain organic chemicals that can contribute to indoor VOC levels. During product usage and storage, these compounds are released into the air, potentially causing indoor air quality issues.
Common sources of VOC emissions from building materials include paints, paint strippers, varnishes, finishes, stains, adhesives, caulks, sealants, coatings, vinyl flooring, carpets, and pressed wood products. Even plumbing adhesives and sealants can contribute to VOC levels indoors.

Other often overlooked sources of VOCs include: Dry cleaned clothing, art and craft products such as glues and permanent markers, photo copiers and printers that use correction fluids and carbonless copy paper, cigarette smoking, wood burning stoves, vehicle exhaust, pesticides, industrial emissions from oil and gas extraction and processing, and Freons released from air conditioning or refrigeration appliances are additional sources of concern.

Moulds are fungi that thrive in the form of multicellular filaments known as hyphae, which spread to create a network or colony called mycelium. While there are thousands of known mould species, only a smaller subset is commonly found in indoor environments. Mould can be present even when not visibly detected, referred to as "hidden mould." This becomes significant as certain chemicals called Mould Volatile Organic Compounds (MVOCs) are released as moulds digest their food sources.

The presence of MVOCs in indoor spaces can serve as an indicator of active mould growth. Prolonged exposure to these MVOCs can have severe health effects, especially on vulnerable groups.

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