Medical Effects: Formaldehyde

Formaldehyde in Our Homes and Health, Department of Natural Resources, Ball State University

[Wood smoke has formaldehyde in it.] Indoor Air Quality Notes:

No. 1, 2nd Ed., Summer, 1989
Thad Godish, Ph.D., Director
Indoor Air Quality Research Laboratory

There is increasing scientific evidence to suggest that formaldehyde contamination of residential and nonresidential indoor environments may be responsible for a variety of irritating symptoms which appear to be building related. Recognition that formaldehyde exposure can cause irritating symptoms in sensitive individuals has prompted governments in Denmark, Sweden, the Netherlands, Italy, Finland, West Germany, and Canada to adopt or propose the adoption of indoor air quality standards for formaldehyde to limit exposures. Concerns about acute health effects associated with urea-formaldehyde foam insulation, as well as a potential cancer risk, has resulted in bans on the use of urea-formaldehyde foam insulation for residential applications in the United States (subsequently voided) and Canada.

The Nature of the Health Problem
Formaldehyde is a potent eye, upper respiratory and skin irritant. Evidence from several studies also indicates that it causes central nervous system effects, including headaches, fatigue, and depression. It also has the potential for causing asthma and inducing asthmatic attacks as a nonspecific irritant. Additionally, animal studies suggest that formaldehyde is a potential human carcinogen.

Recent epidemiological studies of occupationally-exposed individuals suggest that formaldehyde causes human cancer. Studies of residents of mobile homes exposed to formaldehyde above 0. 1 0 ppm for 1 0 + years indicate a significantly increased risk of throat cancer. This increased risk is approximately 2 in 10,000.

Although cancer concerns have received the major share of public and regulatory attention, investigations of consumer complaints and epidemiological studies indicate that the acute irritating symptoms which are associated with residential formaldehyde exposures are a very significant public health problem.

Presumptive Evidence for a Causal Relationship
Presumptive evidence for a cause/effect relationship between reported health problems and the indoor environment of an individual's home includes: (1) Symptoms commonly occur in more than one family member. (2) Symptoms are often most severe in the individuals) who spend the most time at home, e.g., homemakers, infants, retirees. Such individuals have the longest formaldehyde exposure duration. (3) Symptoms often diminish in severity when affected individuals are away from the home environment. Extended absences usually result in marked improvement. Note: When this is not the case, the new environment may also have significant formaldehyde contamination. (4) Symptoms diminish in severity when home environment is provided significant continuous ventilation by opening windows and/o, doors. (5) Symptoms show a distinct seasonal pattern. Onset can be related to a) the beginning of the heating season, b) increased indoor relative humidity, or c) change in daily activities which result in more time spent indoors. Diminished symptom severity may be associated with a) cold dry outdoor weather and b) summertime ventilation of home. (6) Symptom onset may be associated in time to a) moving into a new home (conventional or mobile), b) recent house remodeling, c) acquisition of new furnishings, d) insulating home with urea-formaldehyde foam, e) a change in activity level. (7) Symptoms reported by visitors to affected home

Presumptive evidence for a cause/effect relationship between reported building-related illness symptoms and formaldehyde contamination of an individual's home includes: (1) Symptoms are similar to those reported by workers who are occupationally exposed. (2) Short-term human exposure studies have shown irritation of eyes, nose and throat at concentrations as low as 0.10 ppm. (3) Symptoms can be related to indoor humidity levels. Symptoms are most severe when humidity levels are 50% or greater. When humidity is less than 35%, symptoms diminish in severity. (4) Symptom onset may occur in nonresidential environments where elevated formaldehyde levels are common, e.g. furniture stores. clothing stores, clothing sections of department stores. (5) Presence of potent formaldehyde sources such as particleboard subflooring, urea-formaldehyde foam, extensive quantities of either particleboard or hardwood plywood paneling, cabinets and furniture. (6) Peak formaldehyde levels of circa 0.06 ppm or higher. (7) Symptom severity increases with formaldehyde concentrations. (8) Symptoms most severe in new conventional or mobile homes.

Although apparent formaldehyde/building-related illness symptoms may be similar to other common ailments such as colds, they may be distinguished by their persistence, recurrence, and distinct association with certain indoor environments. In addition, several symptoms appear to be unique to formaldehyde/building-related health problems. These include unusual fatigue and unusual thirst. The former is particularly notable.

Evidence for Causation
Recent scientific studies indicate that formaldehyde exposures are capable of causing symptoms in sensitive individuals at concentrations that are commonly found in a wide variety of American homes.

At formaldehyde levels typical of many mobile and modular homes. (0.35 ppm), Danish workers have reported a significantly high prevalence of the following symptoms (as compared to a control population): eye, nose, and throat irritation, headache, abnormal tiredness, menstrual irregularities, and unnatural thirst. Canadian studies of residents of urea-formaldehyde foam-insulated (UFFI) houses have indicated a dose-response relationship between the formaldehyde concentrations in UFFI houses and the following symptoms: dizziness, diarrhea, eye irritation, nosebleed, cough and sputum production. The average formaldehyde concentration of the UFFI houses surveyed was a very low 0.045 ppm. Interestingly, UFFI residency was associated with a significant increase in the objective symptoms, nasal airway resistance, and auquamous metaplasia of nasal epithelial cells. The latter is considered to be a response to irritation.

Studies have been conducted at Ball State University which have demonstrated a dose-response relationship between the level of formaldehyde present in residential environments such as mobile homes and homes with particleboard subflooring and the severity of 16 different symptoms. These include: eye irritation, dry/sore throat, runny nose, cough, sinus irritation, sinus infection, headaches, unusual fatigue, depression, difficulty sleeping, rashes, bloody nose, nausea, diarrhea, chest pain, and abdominal pain. These significant relationships were observed at an average concentration of 0.09 ppm. These studies suggest that low-level formaldehyde exposures (less than 0. 1 0 ppm) common to many homes in the U.S. are sufficient to exacerbate existing symptoms or to cause them directly.

Menstrual Disorders
Several studies have reported that menstrual irregularities/disorders may be related to occupational and/or residential formaldehyde exposures. This relationship apparently is unknown to physicians treating gynecological problems in this country. The implications of a formaldehyde link to menstrual irregularities is significant since some treating physicians recommend a hysterectomy as a means of treating severe menstrual problems. Because a hysterectomy has significant reproductive implications, it is important that formaldehyde exposure be seriously evaluated as an etiological factor by gynecologists and other treating physicians and those affected. It is particularly likely to be a factor where formaldehyde levels are high such as in mobile or modular homes and in residences with particleboard subflooring. Absence from the elevated formaldehyde environment for a month or more should provide an indication whether the menstrual disorder may be associated with formaldehyde exposure.

Formaldehyde--Sources and Levels
Although formaldehyde is used in a large variety of consumer products, only a few release quantities of free formaldehyde sufficiently to significantly contaminate indoor air. Problem products which may include particleboard subflooring, paneling, cabinetry, furniture, hardwood plywood paneling, use urea-formaldehyde (U-F) resins in their manufacture. For wood products these resins are used as interior-grade adhesives.

U-F resins are chemically unstable. They may release free formaldehyde from the volatilizable, unreacted formaldehyde trapped in the resin and from the hydrolytic decomposition of the resin polymer itself. It is the release of the unreacted formaldehyde fraction which is primarily responsible for the high initial indoor formaldehyde levels associated with the new mobile homes, conventional homes with particleboard subflooring and homes recently insulated with ureaformaldehyde foam.

The release of most of the unreacted formaldehyde may occur in approximately 6 months depending on sources present. After most of the volatile formaldehyde is released, indoor levels may only be a fraction of those when the products were new. A 50 + percent decline is common.

Although a significant decline can be expected, the problem does not go away as commonly believed. Significant continuous formaldehyde release can be expected as the resin polymer undergoes hydrolytic decomposition. Because of this, release of free formaldehyde from U-F products can be expected to continue for an indefinite period.

Formaldehyde-releasing products differ in their emission potential. Consequently, indoor formaldehyde levels will be determined to a considerable degree by the nature of formaldehyde sources present. Additionally, they will also be determined by the quantity of source material used in the building interior. Despite common belief that indoor levels are due to the additive emissions of all sources present, laboratory studies show that major formaldehyde sources interact. This interaction results in a number of outcomes from source suppression to slight augmentation to complete additivity.

Most homes have measurable formaldehyde levels. Homes in which formaldehyde contamination appears to be associated with relatively low-level sources such as furniture, one paneled room, etc. measured formaldehyde levels in the range of 0.02 to 0.07 ppm with peak levels typically 0.05 to 0.06 ppm. Homes insulated with U-F foam (1 or more years after installation) will have formaldehyde levels in the range of 0.03 to 0.13 ppm with peak levels in individual homes in the range of 0.07 to 0.13 ppm. Although U-F foam-insulated homes have received the most notoriety and, of course, regulatory attention, it must be pointed out that peak formaldehyde levels in such homes are relatively low. On the other hand, conventional homes with particleboard subflooring will have measured levels of formaldehyde in the range of 0.06 to 0.15 ppm with peak levels in the range of 0.10 - 0.15 ppm. It is the mobile home, however, that exposes its residents to the highest formaldehyde levels. Typically, peak formaldehyde levels in mobile homes have been in the range of 0.20 - 0.50 ppm with values as high as 1-2 ppm reported for mobile homes manufactured before 1980. In most new mobile homes formaldehyde levels are usually less than 0.40 ppm and are typically in the range of 0.10 to 0.30 ppm.

Cabinetry & Furniture
Two of the most overlooked problems of residential formaldehyde contamination and building-related symptoms have been those associated with cabinets and furniture. Kitchen and bathroom cabinets alone have the potential for causing residential formaldehyde to rise to levels of 0.10 ppm or higher. particularly when they are new. Almost all hardwood cabinets, including solid wood, can be expected to release significant quantities of free formaldehyde into living spaces of homes. Typical materials used in cabinet manufacture include particleboard, medium-density fiberboard, and hardwood plywood. Medium-density fiberboard is the most potent source of formaldehyde found in residences. It is commonly used in cabinet manufacture as a core material overlain by hardwood plys. It is typically 5/8 inches thick and looks like a thick hardboard. However, hardboards such as Masonite are usually 1/4 inch and do not use U-F adhesives. Particleboard is often used as shelving, as core material for hardwood plys, and as countertops. In countertops, the bottom surface is not covered by barriers such as Formica and is considered to be a potent source of formaldehyde. It is not uncommon for cabinets to be made of good quality hardwood plywood. Even such cabinets are seen to be potent sources of formaldehyde, but less so than those constructed of par-ticleboard and/or medium density fiberboard. It is not unusual for cabinets to be constructed of all 3 materials- particleboard, medium-density fiberboard, and hardwood plywood.

Most wood furniture available commercially is constructed of wood products using urea-formaldehyde resins. Particularly significant are those using medium-density fiberboard and particleboard. These typically serve as core materials overlain by hardwood plys, or in the case of inexpensive furniture, a paper-based or plastic laminate.

Cabinets made from hardwood plywood or from solid wood, as well as solid wood furniture, may be significant sources of formaldehyde. The formaldehyde source is an acid-catalyzed wood finish containing urea-formaldehyde, particularly in the first six months after application. These acid-catalyzed finishes are almost universally applied to hardwood plywood cabinets manufactured in the U.S., and their use is widespread on solid wood and hardwood plywood household furniture. Such finishes are commonly applied to hardwood floors and prefinished wood materials.

Environmental Factors
Levels of formaldehyde inside a residence or other type of building structure depend not only on the potency and quantity of sources present but also on environmental conditions which exist both on the inside and outside. Particularly significant is the inside temperature and relative humidity. As a general rule in the temperature range of 65 to 86 degrees F, a temperature increase of 10 degrees F will result in an approximate two-fold increase in formaldehyde levels. Conversely, a decrease of 10 degrees F will result in a 5O% reduction in levels. Less significant, but nevertheless important, is the effect of humidity. An increase in relative humidity from 30-70% can be expected to result in an approximate 40% increase in formaldehyde levels.

Low relative humidity's during the winter period in many northern residences are in part a major cause of the significantly lower formaldehyde levels reported for homes under winter conditions. The effect of low humidity is particularly significant in UFFI homes.

In addition to low humidity, lower wintertime formaldehyde levels are due to increased infiltration rates which lower formaldehyde levels by dilution. Increased infiltration rates are associated with large indoor/outdoor temperature differences and higher wind speeds. The greater the temperature differential between the inside and outside of a building, the lower the formaldehyde level. Conversely, the smaller the temperature differential the higher the formaldehyde concentration. In the latter case, such temperature conditions are common in spring and fall months. Formaldehyde levels can be standardized to a given indoor/outdoor temperature differential using the following equation: Cs = Cm + 0.0016 delta-T where Cs = standardized formaldehyde concentration, Cm = measured formaldehyde concentration, and delta-T = the indoor/outdoor temperature difference at the time of testing.

Maximum formaldehyde values in general occur under warm, humid conditions, particularly when the residence is closed. Elevated formaldehyde can be expected in northern residences in the spring and fall if home ventilation by opening windows is practiced in the summer months and in the spring, summer, and autumn months when air conditioning is used. In warm, humid climates such as those experienced in Florida and southeastern Texas, elevated formaldehyde levels can be expected throughout most of the year. In the drier climates of the West, formaldehyde levels and exposures will be typically lower than in other areas of the country.

Formaldehyde concentrations decrease rapidly with time. Significant decreases can be expected. The decrease time or decay rate will depend on the potency of source materials, their quantity relative to the air volume in the building, and environmental factors such as ventilation, temperature, and relative humidity. The more potent the source and greater the extent of its use, the longer it will take for formaldehyde levels to decrease by a given percentage with time. The higher the temperature and relative humidity and the higher the ventilation rate, the more the formaldehyde level will decrease with time. The decrease is initially very rapid followed by extended, much slower decreases. The release of formaldehyde from source materials will never completely stop.

New Products
Since 1978 there has been a significant improvement in wood products bonded with urea-formaldehyde resins in respect to formaldehyde emissions. Low emission particleboard and hardwood plywood paneling dominate the present market for such wood products. Emissions of formaldehyde from low-emission products are only a fraction of what they were prior to 1978. Despite this, the best grades of particleboard applied as subflooring produce formaldehyde at levels that are typical of peak levels in UFFI houses which can still be described as problem houses. Products have improved, but yet remain sufficiently potent in their formaldehyde releasing potential to cause a variety of irritating symptoms.

Formaldehyde Standards
What level of formaldehyde exposure in a residence is safe? There appears to be no lower level that is safe for everyone. However, the lower the concentration, the lower the risk of adverse health effects.

A variety of official and recommended standards have been applied to formaldehyde exposures. For individuals occupationally exposed, the Occupational Safety and Health Administration (OHSA) permits exposures up to an average of 1 ppm 8 hrs./day, 5 days a week, with a requirement of medical surveillance for employees exposed to concentrations greater than 0.5 ppm.

Occupational standards cannot, however, be validly used to determine the safety of residential exposures. Such standards are designed to provide a relative measure of protection to nominally healthy workers age 18 to 65 for an 8-hour day/5 day work week. Occupational standards cannot easily be extrapolated to residential exposures which may range from 14-24 hours/day, 7 days per week. Exposed individuals in residential environments not only include nominally healthy adults, but also the very young, the old and those with existing ailments. These sub populations may be expected to be at greater health risk to formaldehyde exposures than occupationally-exposed workers.

In response to reported building-related illness health problems associated with residential formaldehyde exposures, several West European countries have proposed or promulgated indoor air quality standards for formaldehyde. For West Germany and the Netherlands this standard is 0.10 ppm maximum concentration; for Denmark 0.12 ppm. Although no residential indoor air quality standards have been established in the United States, the American Society of Heating Refrigerating and Air Conditioning Engineers (ASHRAE) has recommended a voluntary standard of 0.10 ppm, maximum concentration. NASA has had a similar standard for manned space travel of .10 ppm since 1967.

Canada has recently recommended an action level of 0.10 ppm for residential exposures with a target level of 0.05 ppm. This means that the Canadian government has concluded that levels of 0. 1 0 ppm and above are not safe and that the homeowner act to reduce levels. This is in marked contrast to the Department of Housing and Urban Development's target level of 0.40 ppm for new mobile homes. This target level in essence says that HUD believes that human exposures of 0.40 ppm in residential environments are safe. OSHA on the other hand says that exposures to 0.50 ppm over as little as an 8-hour period requires medical surveillance. The HUD target level reflects the ability of wood product manufacturers to make products which do not exceed the target level. The target level does not protect public health. Rather than protecting consumers, it provides regulatory sanction for the manufacture of defective products which are a significant threat to public health.

Building-Related Illness Checklists
Checklists have been developed and presented here to assist individuals, public health practitioners, and physicians in evaluating the potential relationship between an individual's health problems and the indoor environment of his/her residence or place of employment.

The household symptom checklist summarizes a variety of symptoms or health problems which, although they may be nonspecific, have been associated with formaldehyde exposures. These symptom/health problems usually are persistent or recurring and generally do not have an easily recognizable etiology. The checklist in itself may suggest a building-related illness health problem since it may show a pattern of household or family illness which may not be recognized in the normal practice of medicine.

Confirmation of Building-Related Illness
An evaluation of responses to the attached checklists may help to identify a building-related health problem. A strong association between the reported illness and the indoor environment is suggested with increasing frequency of positive responses.

Particularly significant are responses to items which indicate that symptom severity decreases with absence from the home or with significant home ventilation. The former, however, should be viewed with some caution. Removing an individual from his/her home not only changes exposures to air contaminants such as formaldehyde, but it also may change lifestyle patterns, type of food consumed, etc. Additionally, one must also assume that the new environment has less contamination than the existing one. In many cases the new environment itself may also pose a building-related health problem. To minimize changes in lifestyle factors, eating habits, etc. a confirmation protocol based on providing significant ventilation to the home environment is recommended.

Note #2 - Residential Formaldehyde Control available on request. Please send a self-addressed, stamped envelope for each request.


For each item respond by Checking yes, no, don't know or not applicable, in the adjacent column.

Yes No Know N/A

  1. Symptoms reported by more than one family member.
  2. Irritating symptoms most severe in family member who spends
    most time at home.
  3. Symptoms severe in infants or very young children.
  4. Symptoms become less severe when individual is absent from
    home with longer periods showing marked improvement.
  5. Symptoms diminish in severity when home is provided
    significant continuous ventilation.
  6. Symptoms exhibit a seasonal pattern.
  7. Onset of symptoms can be associated in time with:
    a. moving into a new conventional or mobile home
    b. recent house remodeling
    c. acquisition of new furnishings
    d. insulating home with urea-formaldehyde foam
  8. Symptoms reported in visitors to individual's home.



Yes No Know N/A

  1. Symptoms most severe during warm humid weather.
  2. Symptoms least severe on cold dry winter days (in colder
  3. Symptoms of eyes, upper respiratory and central nervous
    system (eye, upper respiratory and CNS effects).
  4. Peak formaldehyde levels of circa 0.06 ppm or higher.
  5. Symptom onset in environments where elevated formaldehyde
    levels are common, e.g. clothing stores, clothing sections of
    department stores, furniture stores, etc.
  6. Presence of major formaldehyde sources.
    a. particleboard subflocring
    b. paneling - hardwood plywood, particleboard
    c. cabinets - particleboard, medium density fiberboard,
    hardwood plywood
    d. wood furniture - particle board, medium density fiberboard,
    hardwood plywood
    e. urea-formaldehyde foam insulation
    f. acid-catalyzed finished wood materials - cabinets, furniture,
    hardwood floors
  7. Symptoms very severe in residents of mobile homes or new
    homes with particleboard subflooring.
  8. Symptoms associated with one area of house where potent
    sources of formaldehyde are located (i.e. closed bedroom)-



For each resident indicate with a check persistent or recurring symptoms/health problems which cannot be associated with any readily diagnosed illness such as cold, flu, etc.

Occupant's Name:


Eye irritation
Eye infection
Dry/sore throat
Excessive phlegm production
Runny nose
Sinus congestion
Sinus infection
Bronchial pneumonia
Shortness of breath
Asthmatic attacks
Disturbed concentration
Unusual fatigue
Difficulty in sleeping
Nasal Sores
Diarrhea/loose stool
Chest pain
Abdominal pain
Menstrual problems
Unusual thirst

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