The Not So Gentle Art of Preservation

What is formaldehyde?

Formaldehyde is a naturally occurring organic compound with the formula CH2O that was discovered in 1867 and isolated in 1892. It is the simplest aldehyde, known by its systematic name methanal, and is formed by oxidising methanol.

Formaldehyde is one part of the larger ‘VOC’ (volatile organic compound) family, where ‘volatile’ means a low boiling point that becomes a gas at normal room temperature. It is extremely reactive and is therefore often mixed into chemical compounds to form stable substances.

At room temperature formaldehyde is a colourless, pungent smelling and flammable gas, which breaks down rapidly in the environment through action with sunlight and bacteria. It metabolises quickly to formic acid in the human body but significantly does not accumulate.

What is it used for?

Used industrially for nearly a century, it is employed by at least 85 manufacturing sectors most famously as a preservative but also for products such as paint, varnish, engine components, cosmetics, disinfectants, medicines, adhesives, inks, and wrinkle-free fabrics. In construction, formaldehyde is widely used as a binder in insulation products as well as an adhesive in MDF, plywood and other timber panel products. Most important in the context of this Blog, formaldehyde is used commonly in timber products used to manufacture furniture.

Is it harmful?

Concern about the health effects of exposure to formaldehyde emissions from materials and furniture was first expressed in the 1970s. This occurred at a time when, as result of ever increasing quantities of greenhouse gases being pumped into the atmosphere, buildings became more air-tight. As homes and offices became more air-tight, and continue to do so, the mitigating effects on VOCs of natural leakage and higher air exchange rates were proportionally reduced. Concern was also extended to workers exposed in the manufacture, handling and processing of formaldehyde based products.

The US Environmental Protection Agency (EPA) describes formaldehyde as causing ‘…watery eyes, burning sensations in the eyes and throat, nausea, and difficulty in breathing in some humans exposed at elevated levels (above 0.1 parts per million). High concentrations may trigger attacks in people with asthma. There is evidence that some people can develop a sensitivity to formaldehyde. It has also been shown to cause cancer in animals and may cause cancer in humans. Health effects include eye, nose, and throat irritation; wheezing and coughing; fatigue; skin rash; severe allergic reactions.’

How is it used?

Most manufactured and bonded wood building panels such as plywood and MDF (medium density fiberboard) contain one of two types of formaldehyde-based glues: Phenol-formaldehyde (PF) or Urea-formaldehyde (UF). The water resistant properties of phenol-formaldehyde glue are commonly utlised in the production of exterior wood materials. Urea-formaldehyde glue, cheaper and less tolerant of excessive moisture, is commonly used for interior materials including wall paneling, flooring and cabinetry. However, phenol-formaldehydes are now becoming more commonly used for interior furniture-grade materials.

This shift to phenol-formaldehydes based interior products is important because UF glue out-gasses considerably more formaldehyde than the PF glue and can be a major source of indoor pollution. Current guidance therefore suggest UF resins are not appropriate for internal use and will often have a warning label stamped on the back similar to the following:

“Warning: This product is manufactured with a urea-formaldehyde resin and will release small quantities of formaldehyde. Formaldehyde levels in the indoor air can cause temporary eye and respiratory irritation and may aggravate respiratory conditions or allergies. Ventilation will reduce indoor formaldehyde levels.”

How much is too much?

In its natural state, softwood lumber emits a tiny amount of formaldehyde. While PF-glued products typically emit 10 times the formaldehyde outgassed by softwood, UF resins can release at least 100 times more formaldehyde than the natural wood.

To be more precise the outgassing of formaldehyde is measured in units of micrograms per square meter per hour (µg/m2/hr) and the following are the ranges that have been measured in different UF and PF based products. The difference between UF products and PF/laminated products at the upper levels is striking as is the difference between MDF and plywood.

Particleboard: (UF) 100-2,000 µg/m2/hr

Medium density fiberboard: (UF) 210-2,300 µg/m2/hr

Furniture-grade plywood: (UF) 7-1700 µg/m2/hr

Furniture-grade plywood w/ vinyl or laminate surface: (UF) 3-300 µg/m2/hr

Construction-grade plywood: (PF) 2-83 µg/m2/hr

The outgassing rates for both glues decrease with time. In fact, the half-life of the out-gassing is usually between 3-5 years. This means that during the first 3-5 year period, half of the formaldehyde will have dissipated, during the second 3-5 year period half of the remainder will dissipate and formaldehyde will continue to dissipate at this rate.

These levels are below the World Health Organisation’s guideline figure for the amount of formaldehyde that may be emitted from all product sources and that may be present in ambient air, either inside homes or outside, of 0.1 mg/cubic metre (equivalent to 0.08 parts per million).

The UK’s Building Research Establishment has tested the air in typical British homes and found it to contain about one-quarter of the above level from all sources. The estimated amount contributed by the higher outgassing MDF sources for example is reckoned to be less than one-fifth of the WHO guideline maximum.

The actual emission rate of a particular product containing either PF or UF glue depends on several factors including the quality of the resin, the additives used, the application methods, and the ambient temperature and humidity. And while PF glue is generally less potent than UF glue from the above measurements it is clear there is a wide variation between products.


One significant omission from recent studies was the ventilation rate. Indoor air quality is influenced by both the amount of air getting in and the indoor sources of pollutant emissions which might include construction materials as well as furniture and other household materials.

Ventilation acts by diluting the concentration of the pollutant and removes some of the pollutant from the internal to the external environment. Where ventilation is reduced, so is the ability to remove pollutants. Whereas a combination of weak air tightness and ventilation rates required by the Building Regulations up to and including those of 2006 were usually adequate to control pollutant concentrations, Part F (2010) now calls for a minimum average controlled ventilation rate of 0.3 l/s m-2 of floor area (Passivhaus rate by comparison is even tighter at 0.2 l/s m-2).

The overall conclusion from reviewing these studies is that formaldehyde exposure in the home or office may be of concern only in new buildings but after a year following construction, that concern is considerably reduced.

However, despite low formaldehyde exposure from MDF and even lower from PF plywood products in the home and office, despite Plywood and MDF manufacture being compliant with the most stringent requirements for formaldehyde content defined by the European Standard (EN 622) and despite its common use throughout Europe, homes and offices are becoming more air-tight.  We must therefore welcome MDF as a zero formaldehyde product. Ecologique for example from Medite which Morfus is currently testing is one such product and hopefully plywood manufacturers will be encouraged likewise to develop formaldehyde free versions of their products.

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