400 WORD PUBLIC HEALTH ARTICLE CRITIQUE

Scandinavian Journal of Public Health, 2010; 38: 232–238

ORIGINAL ARTICLE

Sick building syndrome in relation to domestic exposure in Sweden – A

cohort study from 1991 to 2001

B. SAHLBERG, G. WIESLANDER & D. NORBÄCK

Department of Occupational and Environmental Medicine, Uppsala University Hospital and Uppsala University, Sweden

Abstract Background: Most studies on sick building syndrome (SBS) are cross-sectional and have dealt with symptoms among office workers. There are very few longitudinal cohort studies and few studies on SBS in relation to domestic exposures. The aim of this study was to investigate changes in SBS symptoms during the follow-up period and also to investigate changes in different types of indoor exposures at home and relate them to SBS symptoms in a population sample of adults from Sweden. We also wanted to investigate if there was any seasonal or regional variation in associations between exposure and SBS. Methods: A random sample of 1,000 people of the general population in Sweden (1991) was sent a self administered questionnaire. A follow-up questionnaire was sent in 2001. Results: An increased risk for onset of any skin symptoms (risk ratio (RR) 2.32, 1.37–3.93), mucosal symptoms (RR 3.17, 1.69–5.95) or general symptoms (RR 2.18, 1.29–3.70) was found for those who had dampness or moulds in the dwelling during follow-up. In addition people living in damp dwellings had a lower remission of general symptoms and skin symptoms. Conclusions: Dampness in the dwelling is a risk factor for new onset of SBS symptoms. Focus on indoor environment improvements in dwellings can be beneficial both for the inhabitants and the general population. Reducing dampness in buildings is an important factor for reducing SBS symptoms in the general population.

Key Words: Asthma, building dampness, cohort study moulds, indoor environment, sick building syndrome (SBS)

Introduction

Sick building syndrome (SBS) is a set of non-specific

symptoms occurring in a particular building and the

symptoms normally improve or disappear when

people are away from the building. Such non-specific

symptoms are common in the general population [1]

and even more common among people living in

buildings with indoor air problems. The syndrome

has been defined empirically on the basis of case

reports in which the occupants of a specific building

described similar symptoms that were attributed to

indoor climate problems [2]. Various factors, such as

wall-to-wall carpeting, type of ventilation system,

high room temperature, low supply of outdoor air,

and low air humidity have been shown to influence

the prevalence of SBS symptoms [3–5]. Female

gender and history of allergic disorder have been

shown in many studies to be important risk factors

for SBS symptoms [3–6]. In buildings with a CO2 level <800 ppm the risk for SBS symptoms decreased [7] and SBS symptoms can be more common at

personal airflow rates below 10 l/s [8].

Building dampness is a common indoor exposure,

and has been shown to be related to an increased

prevalence of both asthmatic symptoms and SBS

[9–11]. In a review by Bornehag et al. (2001), it was

concluded that dampness in buildings is a risk factor

and there are associations between both self-reported

and observed dampness and symptoms [9]. The

dampness approximately doubles the risk of health

effects [9,10]. Building dampness in Swedish multi-

family residential buildings has been reported to be

related to a pronounced increase of symptoms com-

patible with SBS symptoms [12].

One common indoor source of volatile organic

compounds (VOC) is emissions from fresh paint.

Correspondence: B Sahlberg, Department of Occupational and Environmental Medicine, Uppsala University Hospital and Uppsala University, SE-751 85

Uppsala, Sweden. Tel: þ46 186 113869. Fax: þ46 185 19978. E-mail: [email protected]

(Accepted 7 September 2009)

� 2010 the Nordic Societies of Public Health DOI: 10.1177/1403494809350517

Two recent studies have shown that 26%–32% of the

Swedish population have had the interior of their

dwelling painted during the last year [1,13].

Nowadays most indoor paint in Sweden is water

based [13] and emissions from fresh indoor paint in

the dwelling may cause airway symptoms [13] and

eye irritation [1,14]. In addition, tobacco smoking is

related to many diseases such as chronic obstructive

pulmonary disease (COPD), lung cancer and ischae-

mic heart disease [15]. Some SBS symptoms,

e.g. general symptoms, are also related to tobacco

smoking [16] and some studies have shown that

exposure to environmental tobacco smoke (ETS)

contributes to the occurrence of SBS symptoms [17].

Most studies on SBS are cross-sectional and have

dealt with symptoms among office workers. There

are hardly any longitudinal cohort studies [18,19]

and few studies on SBS in relation to domestic

exposures [1,6,20–22]. Moreover only a few studies

deal with risk factors for SBS symptoms in the

general population [1,19]. To our knowledge there

are no longitudinal studies on SBS symptoms in

relation to home environmental factors. Since a

cross-sectional study does not give strong evidence

on causal relations, there is a need for longitudinal

studies on SBS, especially in the general population.

Aim

The aim of this study was to investigate changes of

SBS and different types of indoor exposures at home

over a 10-year follow-up period (1991–2001) in a

population sample of adults from Sweden. Moreover

we studied the onset of SBS in relation to personal

factors at baseline and home exposure during the

follow up. We also wanted to investigate if there was

any seasonal or regional variation between indoor

exposures and SBS symptoms.

Material and methods

Study population

The study population consisted of a random sam-

ple of 1,000 persons in the general population aged

20–65 years in 1991. The sampling was done by

Statistics Sweden, which is a central government

authority for official statistics and other government

statistics, and in this capacity also has the responsi-

bility for coordinating and supporting the Swedish

system for official statistics. In order to study sea-

sonal effects, the sample was further divided into

four sub-samples (250 subjects in each). The subjects

in each sub-sample received the standardized

self-administered questionnaire during one of the

four seasons (September 1991 to August 1992). The

response rate was 70%. A follow-up questionnaire

was sent after 10 years (September 2001 to August

2002) to all subjects who participated in the first

study (n¼695), following the same division into

seasonal sub-groups as in the first study. The

response rate in the follow-up was 61% (n¼427).

Assessment of symptoms and personal factors

The questionnaire contained questions on age, sex,

hay-fever and smoking habits. Current smokers were

defined as those participants in the interview who

reported smoking, smoking more than one cigarette

per day, and reported ceasing smoking less than a

year ago. The questionnaire contained questions

requiring ‘‘yes’’ or ‘‘no’’ answers on 16 different

SBS symptoms used in earlier investigations [1].

In Table I the SBS symptoms are listed. The recall

period was three months. Work-related symptoms

were not addressed in this study. There was one

question asking whether the symptoms disappeared

or improved when being away from the workplace or

the home environment. However, this information

was not used in this study, which covers symptoms

regardless of the subject’s opinion on causes.

The prevalence of symptoms was calculated for

each of the 16 symptoms. The symptoms were

classified as eye, nasal, throat, facial dermal, or

general symptoms, and the prevalence of subjects

with at least one symptom in each group was

calculated. The prevalence of subjects with at least

one mucous membrane symptom (eye irritation,

swollen eyelids, nasal obstruction, dryness in throat,

sore throat, or irritating cough), dermal symptoms or

general symptoms was calculated.

Assessment of information on the dwelling

The questionnaire requested information on building

age, type of building, type of ventilation system, air

humidification, presence of wall-to-wall carpets, and

four different signs of microbial growth, malodours

or building moisture during the last 12 months. The

questions on building dampness have been validated

in a previous study [23]. The validation was made by

comparing self-reported building dampness by the

inhabitant in the dwelling, with observations on signs

of building dampness made by an occupational

hygienist visiting the dwellings. If the presence of at

least one observed sign of building dampness was

used as the gold standard, sensitivity was 74% and

specificity was 71%. The questionnaire used in the

follow up contained three additional questions on any

Sick building syndrome and domestic exposure: cohort study in Sweden 233

building dampness, any indoor painting, and any

wall-to-wall carpeting in any of the dwellings the

participants had lived in during the 10-year follow-up

period. These questions were used to study associa-

tions with onset of SBS.

Statistical methods

Changes in prevalence of health parameters or

building characteristics were tested by the

McNemar test. For each person, the weekly occur-

rence of any mucosal, dermal or general symptom

was calculated both in the beginning and at the end of

the follow-up period. Onset of any mucosal symptom

was defined as presence of at least one mucosal

symptom at the end of the follow-up period, but

absence of any mucosal symptom in the beginning.

Onset of any dermal or any general symptom was

defined in a similar way. Remission of symptoms

was defined as presence of symptoms (mucosal,

dermal or general) in the beginning and absence of

the particular type of symptom at the end of the

follow up. Multivariate statistical analysis was per-

formed by multiple binominal regression, calculating

relative risk (RR) with 95% confidence interval (CI)

for onset or remission of each type of symptom

group. When studying onset of symptoms, partici-

pants with the particular type of symptoms at base-

line were excluded. When studying remission of

symptoms, only participants with the particular

symptom at baseline were included. In the binomial

models control was made for possible confounding

by keeping age at baseline, gender, current smoking

at baseline, and hay fever at baseline together with the

three home-exposure variables.

In addition, associations between dampness during

the follow-up and onset of symptoms was studied in

different sub-groups separately, stratifying for sex,

hay fever at baseline, smoking at baseline, region at

baseline (southern, mid and northern Sweden), and

the four seasons. In all statistical analyses, two-tailed

tests and a 5% level of significance was applied.

All analyses were done with SAS� system version 9.1.

Results

The follow up study was restricted to those 427

people who participated in both the initial study and

the follow up-study. A comparison between partici-

pants (n¼427) and non-participants (n¼268) gave

the following results: the non-participants did not

differ significantly from the participants with respect

to age, gender, hay fever, doctor’s diagnosed asthma,

or smoking habits at baseline. The initial mean age

was 42 years. The prevalence of asthma had numer-

ically increased and the prevalence of hay fever

had significantly increased (Table I). There were

no significant changes in chronic bronchitis. The

prevalence of current smoking had decreased and the

prevalence of ex-smokers had increased significantly

(Table I). The prevalence of mucosal symptoms

remained unchanged, and any general and any skin

symptoms had decreased. Among individual symp-

toms cold and headache had decreased (Table I).

Some improvements in the home environment

with regard to building dampness and indoor moulds

were observed. Visible indoor mould during the last

year had decreased. Also, mouldy odour and any sign

of building dampness had decreased. Other types of

odour, excluding mouldy odour, had decreased. The

proportion of dwellings with mechanical ventilation

either in living rooms or bedrooms had slightly

increased (Table II). The prevalence of any type of

building dampness had increased, but water leakage,

Table I. The prevalence of asthma, allergies, chronic bronchitis,

smoking habits and type of symptoms among participants in both

studies.

Prevalence (%)

1991

(n¼427)

2001

(n¼427) p-value a

Asthma 7.8 9.7 0.18

Any type of allergy 27 27 1.00

Hay fever 12 16 0.04

Chronic bronchitis 6.9 6.2 0.56

Current smoker 28 19 0.002

Ex-smoker 22 32 <0.0001 Type of symptom

Eye irritation 16 19 0.27

Swollen eyelids 10 9 0.56

Nasal catarrh 12 11 0.61

Nasal obstruction 20 18 0.22

Dryness in the throat 18 17 0.46

Sore throat 8 6 0.08

Irritating cough 7 10 0.06

Any mucosal b

41 43 0.73

Headache 22 17 0.02

Tiredness 35 33 0.35

Sensation of getting a cold 23 16 0.0005

Nausea 6 7 0.32

Any general c

48 42 0.02

Facial itching 9 6 0.11

Facial rash 8 8 1.00

Itching on the hands 9 8 0.78

Rashes on the hands 10 8 0.18

Eczema 13 9 0.06

Any skin d

21 16 0.02

a Differences tested by McNemar statistical test.

b The prevalence

of subjects with at least one symptom classified as mucosal. c The

prevalence of subjects with at least one symptom classified as

general. d The prevalence of subjects with at least one symptom

classified as skin.

234 B. Sahlberg et al.

sign of floor dampness and visible moulds had

decreased during the study period. A large propor-

tion (70%) had painted indoors during the follow-up

period and nearly a third of these had used solvent-

based paints. Furthermore 31% of the subjects had

lived in a dwelling with wall-to-wall carpet and a third

had lived in a dwelling with some type of building

dampness.

The cumulative incidence of subjects with new

onset of at least one symptom in each group was 12%

for skin symptoms, 28% for mucosal symptoms and

25% for general symptoms. For headache the cumu-

lative incidence was 10% and for tiredness it was

15%. An increased onset for any skin, mucosal or

general symptoms was found for those who had any

type of building dampness in the dwelling during

follow up. We did not find any relations between

onset of any symptoms and indoor painting, either

for any type of paint or for use of solvent-based

paints. Among personal factors hay fever at baseline

was related positively to onset of skin and mucosal

symptoms, and age was related to onset of mucosal

membrane symptoms (Table III). We also analyzed

the relationship between specific mucosal symptoms

such as eye, nose and throat and building factors and

personal factors. Onset of eye symptoms (RR 2.41,

1.38–4.35) and throat symptoms (RR 2.33, 1.10–

4.95) was significantly more common in damp

dwellings.

In the stratified analysis, we analyzed associations

between symptoms and dampness in the dwelling.

There was no consistent gender difference for the

association between onset of any type of symptoms

and dampness in the dwelling. Subjects with hay

fever had a numerically higher RR for onset of

general symptoms and skin symptoms, but confi-

dence intervals were overlapping. No regional or

seasonal differences for RR for onset of any symp-

toms in relation to dampness were observed.

Smokers at baseline had a consistently higher RR

for onset of general, skin and mucosal symptoms in

relation to dampness as compared to non smokers.

The RR was two to eight times higher for smokers,

but confidence intervals were partly overlapping.

Remission from general symptoms or skin symptoms

was less likely in subjects with dampness in the

dwelling, and remission from general symptoms was

less likely if the dwelling had been painted indoors

during follow up. Moreover, remission from skin

symptoms was less likely in subjects with hay fever at

baseline (Table IV).

Discussion

The main findings in this study were that the

people who had any type of building dampness

had a significantly higher incidence for general

symptoms, skin symptoms and mucosal symptoms.

Table III. Relationship between onset of weekly symptoms, building factors and personal factors.

Type of symptoms

General a

(RR 95% CI) b

Skin c

(RR 95% CI) b

Mucus d

(RR 95% CI) b

Female gender 1.45 (0.96–2.21) 1.59 (0.88–2.89) 1.33 (0.88–2.02)

Age (10y) 0.90 (0.74–1.11) 1.11 (0.90–1.48) 1.11 (1.00–1.34)*

Hay fever 1.46 (0.78–2.73) 2.76 (1.30–5.84)* 2.30 (1.22–4.32)*

Current tobacco smoker 0.95 (0.57–1.59) 1.67 (0.86–3.21) 0.73 (0.44–1.22)

Any type of building dampness 2.32 (1.37–3.93)* 3.17 (1.69–5.95)* 2.18 (1.29–3.70)*

Indoor painting 1.42 (0.91–2.21) 1.23 (0.68–2.23) 1.11 (0.71–1.73)

Any wall-to-wall-carpet 0.64 (0.40–1.01) 0.72 (038–1.38) 0.79 (0.50–1.24)

a Subjects with onset of at least one symptom classified as general.

b Relative risk (RR) and 95% confidence interval.

c Subjects with onset of at

least one symptom classified as skin. d Subjects with onset of at least one symptom classified as mucosal. *p < 0.05

Table II. The prevalence of environmental factors in the current

dwelling of subjects who participated both in the initial study 1991

and in the follow up in 2001.

Prevalence

(%)

Prevalence

(%)

(n¼427) (n¼427)

1991 2001 p-value a

Any type of pet at home 40 36 0.09

Indoor painting in the last

12 months

30 25 0.10

General mechanical ventilation

(in bedroom or living room)

20 22 0.32

Other type of odour

(mouldy odour excluded)

7.9 1.8 0.0001

Water leakage last 12 months 11 7.3 0.10

Signs of floor dampness

last 12 months

5.8 3.3 0.08

Visible moulds last 12 months 5.3 1.5 0.002

Mouldy odour last 12 months 2.8 0.5 0.008

Any type of building dampness b

18 24 0.02

a Differences tested by McNemar statistical test.

b Subjects report-

ing at least one factor regarded as dampness.

Sick building syndrome and domestic exposure: cohort study in Sweden 235

Furthermore, those with hay fever had a higher

incidence for skin symptoms and mucosal symptoms,

and a lower remission for skin symptoms. In addition

subjects living in damp dwellings had a lower remis-

sion of general symptoms and skin symptoms, and

those in dwellings that had been painted indoors had

a lower remission of general symptoms. In our study

the incidence of asthma had numerically increased

and the prevalence of hay fever had increased. This is

in accordance with other studies on asthma in the

population [28,29].

Some methodological issues in this study need to

be addressed. The study is solely based on self-

reported data with no objective measurement, and

the information on building dampness in the longi-

tudinal analysis was collected retrospectively.

Moreover, good reproducibility of self-administered

questions on building humidity, visible moulds, and

flooding has been reported [23,24]. The questions

used in this study have been validated in earlier

studies by Norbäck et al. (1999) with regard to the

relationship between observed and self-reported

dampness. The sensitivity and specificity for the

presence of at least one sign of building dampness

were 74% and 71% respectively.

Recall bias can be a potential problem, as is the

possibility that the subjects overestimate or underes-

timate their personal symptoms and/or signs of

indoor dampness. Moreover, studies have established

that there was no difference in the reporting rate of

indoor dampness between symptomatic and asymp-

tomatic subjects [25] and that both groups tended to

underestimate the true observed indoor dampness

[26]. Selection bias can occur, both because of an

incorrect study design and as a result of a low

response rate. The response rate in the initial study

was 70%, and of these 61% participated in the

follow-up study. Furthermore, the participants who

were lost during follow up did not differ from the

participants in baseline characteristics on age,

gender, hay fever, doctor’s diagnosed asthma, or

smoking habits. Thus, we would not expect any

major bias due to drop outs. One limitation however

is that the long follow-up period may lead to transient

symptoms related to exposure being missed, and only

permanent symptoms remaining after exposure being

registered.

Visible indoor moulds, mouldy odour, other type

of odour and any type of building dampness had

decreased significantly, possibly due to better main-

tenance and other improvements, suggesting less risk

for impaired health. Moreover, the number of dwell-

ings with mechanical ventilation had slightly

increased. The prevalence of any building dampness,

water leakage, sign of floor dampness and visible

moulds had decreased during the study period. This

illustrates that the increased focus on damp buildings

in Swedish dwellings have resulted in indoor envi-

ronmental improvements. A large amount of subjects

had painted indoors during the follow-up period. We

found that solvent-based paints were more com-

monly used by subjects renovating their dwelling

compared with those who used professional painters.

Studies on indoor painting show that professional

painters in Sweden almost exclusively use water-

based paints [13]. Although subjects renovating their

dwelling were using solvent-based paints to a larger

extent, we did not find any relation between onset of

any symptoms and use of solvent-based paints.

However, the remission from general symptoms was

less likely in subjects who had their home painted

indoors with any type of paint.

A higher onset of general, skin and mucosal

symptoms was observed for all subjects with any

type of dampness in the dwelling. Analyses for

specific symptoms showed that subjects with any

type of dampness in the dwelling also had a

significantly higher onset for throat symptoms and

eye symptoms. Two review articles by Bornehag et al.

(2001, 2004) have concluded that building dampness

Table IV. Relationship between remission of weekly symptoms, building factors and personal factors.

Type of symptoms

General a

(RR 95% CI) b

Skin c

(RR 95% CI) b

Mucus d

(RR 95% CI) b

Female gender 0.79 (0.43–1.47) 0.62 (0.18–2.05) 0.80 (0.41–1.55)

Age (10y) 1.11 (0.82–1.48) 1.00 (0.43–1.22) 0.90 (1.00–18.66)

Hay fever 2.18 (0.99–4.19) 0.18 (0.05–0.70)* 0.47 (0.19–1.14)

Current tobacco smoker 1.28 (0.59–2.79) 0.74 (0.20–2.74) 0.92 (0.39–2.16)

Any type of building dampness 0.48 (0.23–0.99)* 0.24 (0.07–0.83)* 0.46 (0.21–1.02)

Indoor painting 0.43 (0.21–0.86)* 0.51 (0.15–1.69) 1.13 (0.56–2.27)

Any wall to wall carpet 1.57 (0.80–3.10) 1.42 (0.41–4.97) 1.21 (0.58–2.53)

a Subjects with remission of all symptoms classified as general.

b Relative risk (RR) and 95% confidence interval.

c Subjects with remission of

all symptoms classified as skin. d Subjects with remission of all symptoms classified as mucosal. *p < 0.05

236 B. Sahlberg et al.

is a risk factor for airway symptoms and also other

symptoms such as tiredness and headache, but these

conclusions are mainly based on cross-sectional data.

In addition, our results show that remission from

general symptoms or skin symptoms was less likely in

subjects with any type of dampness in the dwelling.

Similar results have been presented for respiratory

symptoms and building dampness [27].

No major sex, regional and seasonal difference was

observed for the association between dampness in the

dwelling and onset of symptoms. To our knowledge,

studies on seasonal or regional differences on asso-

ciations are rare. Our data indicate that tobacco

smoking might enhance the effect of building damp-

ness on incidence of SBS, but this finding needs to be

confirmed in larger studies.

In cross-sectional data female sex has been shown

to be an important risk factor for SBS symptoms

[3–6]. but our incidence data imply that there is no

difference in onset of SBS between females and

males. One cause of this discrepancy could be that

most other studies on SBS are cross-sectional and

present prevalence for SBS symptoms.

In conclusion, dampness and moulds in the dwell-

ing are a risk factor for onset of new SBS symptoms.

In addition, subjects living in damp dwellings have a

lower remission of general and skin symptoms.

Moreover, hay fever may increase the onset and

decrease the remission from SBS. Smoking may

enhance the association between dampness and

onset of SBS symptoms. The substantial reduction

of tobacco smoking in Sweden is expected to have a

beneficial impact on public health, with less exposure

to environmental tobacco smoke and less smoke-

related diseases in the future.

Acknowledgements

This study was supported by Uppsala University

hospital in Uppsala Sweden.

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