PVC flooring at home and development of asthma among young children in Sweden, a 10-year follow-up.

UNLABELLED: The incidence of asthma and allergy has increased throughout the developed world over the past decades. During the same period of time, the use of industrial chemicals such as phthalates, commonly used as plasticizers in polyvinylchloride (PVC) flooring material, has increased. The aim of this study was to investigate whether PVC flooring in the home of children in the age of 1-5 years is associated with the development of asthma in 5- and 10-year follow-up investigations (n = 3228). Dampness in Buildings and Health Study (DBH Study) commenced in 2000 in Värmland, Sweden. The current analyses included subjects who answered all baseline and follow-up questionnaires. Logistic regression analyses were applied to questionnaire results. Children who had PVC floorings in the bedroom at baseline were more likely to develop doctor-diagnosed asthma during the following 10-year period when compared with children living without. There were indications that PVC flooring in the parents' bedrooms was strongly associated with the new cases of doctor-diagnosed asthma when compared with child's bedroom. Our results suggest that PVC flooring exposure during pregnancy could be a critical period in the development of asthma in children at a later time; prenatal exposure and measurements of phthalate metabolites should be included in the future. PRACTICAL IMPLICATIONS: This study has found that PVC flooring material in early life was related to incidence of asthma during the following 10 years when compared with other flooring materials and especially when comparing with wood flooring type.The study has further indicated that PVC flooring in the parents' bedroom (proxy for prenatal exposure) was more associated with the development of asthma than PVC in the child's bedroom was. Our results suggest that PVC flooring exposure during pregnancy could be a critical period in the development of asthma in children at a later time. In future prospective cohort study, prenatal exposure and measurements of phthalate metabolites should be included.

Residential culturable fungi, (1-3, 1-6)-ß-d-glucan, and ergosterol concentrations in dust are not associated with asthma, rhinitis, or eczema diagnoses in children.

Qualitative reporting of home indoor moisture problems predicts respiratory diseases. However, causal agents underlying such qualitative markers remain unknown. In the homes of 198 multiple allergic case children and 202 controls in Sweden, we cultivated culturable fungi by directly plating dust, and quantified (1-3, 1-6)-ß-D-glucan and ergosterol in dust samples from the child's bedroom. We examined the relationship between these fungal agents and degree of parent or inspector-reported home indoor dampness, and microbiological laboratory's mold index. We also compared the concentrations of these agents between multiple allergic cases and healthy controls, as well as IgE-sensitization among cases. The concentrations of culturable fungal agents were comparable between houses with parent and inspector-reported mold issues and those without. There were no differences in concentrations of the individual or the total summed culturable fungi, (1-3, 1-6)-ß-D-glucan, and ergosterol between the controls and the multiple allergic case children, or individual diagnosis of asthma, rhinitis, or eczema. Culturable fungi, (1-3, 1-6)-ß-D-glucan, and ergosterol in dust were not associated with qualitative markers of indoor dampness or mold or indoor humidity. Furthermore, these agents in dust samples were not associated with any health outcomes in the children.

Validation of a parental questionnaire to identify atopic dermatitis in a population-based sample of children up to 2 years of age.

BACKGROUND: Validated eczema questionnaires have been available for schoolchildren only, but the incidence of atopic dermatitis (AD) is highest during infancy. OBJECTIVE: To validate a parental questionnaire to identify AD in children up to 2 years of age. METHODS: Parents of 476 children answered a written questionnaire prior to an examination by a physician. Sensitivity, specificity, predictive values and test-retest reliability of the questionnaire were assessed. RESULTS: A total of 245 (51%) girls and 231 (49%) boys, aged 1-24 months, with and without physician-diagnosed AD participated. Seventy-one children (15%) had physician-diagnosed AD. Validation of the questionnaire by comparisons with physicians' diagnoses showed a sensitivity of 0.87 (95% confidence interval, CI, 0.77-0.94) and a specificity of 0.98 (95% CI, 0.96-0.99). The positive predictive value was 0.90 (95% CI, 0.80-0.96) and the negative predictive value was 0.98 (95% CI, 0.96-0.99). CONCLUSION: The questionnaire identified AD in children aged 0-2 years with high accuracy.

PVC flooring is related to human uptake of phthalates in infants.

UNLABELLED: Polyvinyl chloride (PVC) flooring material contains phthalates, and it has been shown that such materials are important sources for phthalates in indoor dust. Phthalates are suspected endocrine-disrupting chemicals (EDCs). Consecutive infants between 2 and 6 months old and their mothers were invited. A questionnaire about indoor environmental factors and family lifestyle was used. Urinary metabolites of the phthalates diethyl phthalate (DEP), dibutyl phthalate (DBP), butylbenzyl phthalate (BBzP), and dietylhexyl phthalate (DEHP) were measured in the urine of the children. Of 209 invited children, 110 (52%) participated. Urine samples were obtained from 83 of these. Urine levels of the BBzP metabolite monobenzyl phthalate (MBzP) was significantly higher in infants with PVC flooring in their bedrooms (P < 0.007) and related to the body area of the infant. Levels of the DEHP metabolites MEHHP (P < 0.01) and MEOHP (P < 0.04) were higher in the 2-month-old infants who were not exclusively breast-fed when compared with breast-fed children. The findings indicate that the use of soft PVC as flooring material may increase the human uptake of phthalates in infants. Urinary levels of phthalate metabolites during early life are associated with the use of PVC flooring in the bedroom, body area, and the use of infant formula. PRACTICAL IMPLICATIONS: This study shows that the uptake of phthalates is not only related to oral uptake from, for example, food but also to environmental factors such as building materials. This new information should be considered when designing indoor environment, especially for children.

Predicted risk of childhood allergy, asthma, and reported symptoms using measured phthalate exposure in dust and urine.

UNLABELLED: The associated risk of phthalate exposure, both parent compounds in the home and their metabolites in urine, to childhood allergic and respiratory morbidity, after adjusting for exposures of indoor pollutants, especially bioaerosols, was comprehensively assessed. Levels of five phthalates in settled dust from the homes of 101 children (3-9 years old) were measured, along with their corresponding urinary metabolites. Other environmental risk factors, including indoor CO2, PM2.5, formaldehyde, 1,3-ß-D-glucan, endotoxin, allergen and fungal levels, were concomitantly examined. Subject's health status was verified by pediatricians, and parents recorded observed daily symptoms of their children for the week that the home investigation visit took place. Significantly increased level of benzylbutyl phthalate, in settled dust, was associated with test case subjects (allergic or asthmatic children). Higher levels of dibutyl phthalate and its metabolites, mono-n-butyl phthalate, and mono-2-ethylhexyl phthalate were found to be the potential risk factors for the health outcomes of interest. Similarly, indoor fungal exposure remained a significant risk factor, especially for reported respiratory symptoms. The relative contribution from exposure to phthalates and indoor biocontaminants in childhood allergic and respiratory morbidity is, for the first time, quantitatively assessed and characterized. PRACTICAL IMPLICATIONS: For asthmatic and allergic children living in subtropical and highly developed environments like homes in Taiwan, controlling environmental exposure of phthalates may be viewed as equally important as avoiding indoor microbial burdens, for the management of allergy-related diseases. It is also recognized that multidisciplinary efforts will be critical in realizing the true underlying mechanisms associated with these observations.

Children's health and its association with indoor environments in Danish homes and daycare centres - methods.

UNLABELLED: The principle objective of the Danish research program 'Indoor Environment and Children's Health' (IECH) was to explore associations between various exposures that children experience in their indoor environments (specifically their homes and daycare centers) and their well-being and health. The targeted health endpoints were allergy, asthma, and certain respiratory symptoms. The study was designed with two stages. In the first stage, a questionnaire survey was distributed to more than 17,000 families with children between the ages of 1 and 5. The questionnaire focused on the children's health and the environments within the homes they inhabited and daycare facilities they attended. More than 11,000 questionnaires were returned. In the second stage, a subsample of 500 children was selected for more detailed studies, including an extensive set of measurements in their homes and daycare centers and a clinical examination; all clinical examinations were carried out by the same physician. In this study, the methods used for data collection within the IECH research program are presented and discussed. Furthermore, initial findings are presented regarding descriptors of the study population and selected characteristics of the children's dwellings and daycare centers. PRACTICAL IMPLICATIONS: This study outlines methods that might be followed by future investigators conducting large-scale field studies of potential connections between various indoor environmental factors and selected health endpoints. Of particular note are (i) the two-stage design - a broad questionnaire-based survey followed by a more intensive set of measurements among a subset of participants who have been selected based on their responses to the questionnaire; (ii) the case-base approach utilized in the stage 2 in contrast to the more commonly used case-control approach; (iii) the inclusion of the children's daycare environment when conducting intensive sampling to more fully capture the children's total indoor exposure; and (iv) all clinical examinations conducted by the same physician. We recognize that future investigators are unlikely to fully duplicate the methods outlined in this study, but we hope that it provides a useful starting point in terms of factors that might be considered when designing such a study.

Phthalate exposure and asthma in children.

During the last decades more than 100 000 new chemicals have been introduced to the environment. Many of these new chemicals and many common consumer products that include these have been shown to be toxic in animal studies and an increasing body of evidence suggests that they are also impacting human health. Among the suspect chemicals, the endocrine disrupting chemicals (EDCs) are of particular concern. One such chemical group is the phthalates, used in soft poly vinyl chloride (PVC) material and in a huge number of consumer products. During the same period of time that the prevalence of these modern chemicals has increased, there has been a remarkable increase in several chronic illnesses, including asthma and allergy in children. In this article we outline the scientific knowledge on phthalate exposure for asthma and airway diseases in children by examining epidemiological and experimental peer review data for potential explanatory mechanisms. Epidemiological data point to a possible correlation between phthalate exposure and asthma and airway diseases in children. Experimental studies present support for an adjuvant effect on basic mechanisms in allergic sensitization by several phthalates. Despite variations in the experimental design and reported result in the individual studies, a majority of published reports have identified adjuvant effects on Th2 differentiation, production of Th2 cytokines and enhanced levels of Th2 promoted immunoglobulins (mainly IgG1 but also IgE) in mice. A limited amount of data do also suggest phthalate-induced enhancement of mast cell degranulation and eosinophilic infiltration which are important parts in the early inflammation phase. Thus, some of the early key mechanisms in the pathology of allergic asthma could possibly be targeted by phthalate exposure. But the important questions of clinical relevance of real life exposure and identification of molecular targets that can explain interactions largely remain to be answered.

Culturable mold in indoor air and its association with moisture-related problems and asthma and allergy among Swedish children.

UNLABELLED: In a nested case-control study with 198 children with asthmatic and allergic symptoms (cases) and 202 healthy controls in Värmland, Sweden, we have investigated the relationship between mold spore exposure (mean colony-forming unit) indoor and (i) different indexes of moldy odor indoor (observed by professional inspectors and reported by parents), (ii) visible signs of dampness in the homes of the children (observed and reported), and (iii) doctor-diagnosed asthma/allergy in children. No association was found between the spore concentration indoor and moldy odor and signs of visible dampness in the homes. When a semi-quantitative method in distinguishing between moldy houses or non-moldy houses was used, there were no significant differences between the observed indexes of moldy odor or visible signs of dampness (both observed and reported). No association could be found between the spore concentration in indoor air and asthma/allergy in the children. PRACTICAL IMPLICATIONS: Mold spore exposure indoor have been suggested as a possible explanation for airway problems such as asthma and allergy among people living in buildings with moisture-related problems. However, this investigation could not find any associations between the spore concentrations in indoor air and signs of dampness and moldy odor reported by parents or observed by professional inspectors. Neither was there any association between the indoor spore concentration and asthma/allergy among children. With these results, there is no reason for one-time air sampling of mold colony-forming unit (CFU) in indoor air of homes to identify risk factors for asthma/allergy in children living in Scandinavian countries.

PVC--as flooring material--and its association with incident asthma in a Swedish child cohort study.

UNLABELLED: The Dampness in Buildings and Health study (DBH) started in the year 2000 in Värmland, Sweden, with a baseline questionnaire sent to all children (n = 14,077) aged 1-6. Five years later, a follow-up questionnaire was sent to the children who were 1-3 years at baseline. A total of 4779 children participated in both the baseline and the follow-up studies and constitute the study population in this cohort study. The aim of this study was to examine the association between exposure to PVC-flooring in the child's and parent's bedroom in homes of children aged 1-3 and the incidence of asthma, rhinitis, and eczema during the following 5-year period. Adjusted analyses showed that the incidence of asthma among children was associated with PVC-flooring in the child's bedroom (AOR 1.52; 95% CI 0.99-2.35) and in the parent's bedroom (1.46; 0.96-2.23). The found risks were on borderline of significance and should therefore be interpreted with caution. There was further a positive relationship between the number of rooms with PVC-flooring and the cumulative incidence of asthma. PVC-flooring was found to be a stronger risk factor for incident asthma in multifamily homes when compared with single-family houses and in smoking families compared with non-smoking families and in women. PRACTICAL IMPLICATIONS: These longitudinal data from the DBH study found an association between the presence of PVC-flooring in the home and incident asthma in children. However, earlier results from the DBH study have shown that PVC-flooring is one important source for phthalates in indoor dust, and exposure to such phthalates was found to be associated with asthma and allergy among children. This emphasizes the need for prospective studies that focus on the importance of prenatal and neonatal exposure to phthalates in the development of asthma and allergy in children.

Low home ventilation rate in combination with moldy odor from the building structure increase the risk for allergic symptoms in children.

UNLABELLED: There are consistent findings on associations between asthma and allergy symptoms and residential mold and moisture. However, definitions of 'dampness' in studies are diverse because of differences in climate and building construction. Few studies have estimated mold problems inside the building structure by odor assessments. In a nested case-control study of 400 Swedish children, observations and measurements were performed in their homes by inspectors, and the children were examined by physicians for diagnoses of asthma, eczema, and rhinitis. In conclusion, we found an association between moldy odor along the skirting board and allergic symptoms among children, mainly rhinitis. No associations with any of the allergic symptoms were found for discoloured stains, 'floor dampness' or a general mold odor in the room. A moldy odor along the skirting board can be a proxy for hidden moisture problem inside the outer wall construction or in the foundation construction. There are indications that such dampness problems increase the risk for sensitization but the interpretation of data in respect of sensitization is difficult as about 80% of the children with rhinitis were sensitized. Furthermore, low ventilation rate in combination with moldy odor along the skirting board further increased the risk for three out of four studied outcomes, indicating that the ventilation rate is an effect modifier for indoor pollutants. PRACTICAL IMPLICATIONS: This study showed that mold odor at the skirting board level is strongly associated with allergic symptoms among children. Such odor at that specific place can be seen as a proxy for some kind of hidden moisture or mold problem in the building structure, such as the foundation or wooden ground beam. In houses with odor along the skirting board, dismantling of the structure is required for an investigation of possible moisture damage, measurements, and choice of actions. In homes with low ventilation in combination with mold odor along the skirting board, there was even a higher risk of health effects. This emphasizes the need for the appropriate remediation as this is an ever increasing problem in poorly ventilated houses that are damp.

Microbial volatile organic compounds in the air of moldy and mold-free indoor environments.

UNLABELLED: A single-blinded study was performed to analyze whether indoor environments with and without mold infestation differ significantly in microbial volatile organic compounds (MVOC) concentrations. Air sampling for MVOC was performed in 40 dwellings with evident mold damage and in 44 dwellings, where mold damage was excluded after a thorough investigation. The characteristics of the dwellings, climatic parameters, airborne particles and air exchange rates (AER) were recorded. The parameters mold status, characteristics of the interiors and measured climatic parameters were included in the multiple regression model. The results show no significant association between most of the analyzed MVOC and the mold status. Only the compounds 2-methyl-1-butanol and 1-octen-3-ol indicated a statistically significant, but weak association with the mold status. However, the concentrations of the so-called MVOC were mainly influenced by other indoor factors. 2-Methylfuran and 3-methylfuran, often used as main indicators for mold damage, had a highly significant correlation with the smoking status. These compounds were also significantly correlated with the humidity and the AER. The compounds 3-methyl-1-butanol, 2-hexanone, 3-heptanone and dimethyl disulfide were weakly correlated with the recorded parameters, the humidity being the strongest influencing factor. Only 2-methyl-1-butanol and 1-octen-3-ol showed a statistically significant association with the mold status; however, only a small portion (10% in this case) of the total variability could be explained by the predictor mold status; they do not qualify as indicator compounds, because such minor correlations lead to a too excessive part of incorrect classifications, meaning that the diagnostic sensitivity and specificity of these compounds are too low. PRACTICAL IMPLICATIONS: The assumption that mold infestations might be detected by microbial VOC emissions must be considered with great reservation. The major part of the total variability of the measured MVOC concentrations originates from not known influencing factors and/or from factors not directly associated with the mold status of the dwellings (confounders). More specific and sensitive markers for the assessment of the mold status should be found, if the screening for mold infestations should be performed by volatile organic compounds.

Prenatal exposure to acetaminophen and children's language development at 30 months.

OBJECTIVE: To examine prenatal APAP exposure in relation to language development in offspring at 30 months of age. METHOD: A population-based pregnancy cohort study including 754 women who enrolled in the Swedish Environmental Longitudinal, Mother and child, Asthma and allergy (SELMA) study in pregnancy week 8-13. Two exposure measures were used: (1) maternally reported number of APAP tablets taken between conception and enrollment; (2) APAP urinary concentration at enrollment. Language development at 30 months was assessed by nurse's evaluation and parental questionnaire, including the number of words the child used (<25, 25-50 and >50). Main study outcome; parental report of use of fewer than 50 words, termed language delay (LD). RESULTS: 59.2% of women enrolled in weeks 8-13 reported taking APAP between conception and enrollment. APAP was measurable in all urine samples and urinary APAP was correlated with the number of APAP taken during pregnancy (P<0.01). Language delay was more prevalent in boys (12.6%) than girls (4.1%) (8.5% in total). Both the number of APAP tablets and urinary APAP concentration were associated with greater LD in girls but not in boys. The adjusted odds ratio (OR) for LD among girls whose mothers reported >6 vs. 0 APAP tablets was 5.92 (95% confidence interval (CI) 1.10-31.94). The OR for LD in girls whose mothers' urinary APAP was in the highest compared to the lowest quartile was 10.34 (95% CI 1.37-77.86). While it cannot be ruled out, our available data do not support confounding by indication. CONCLUSIONS: Given the prevalence of prenatal APAP use and the importance of language development, these findings, if replicated, would suggest that pregnant women should limit their use of this analgesic during pregnancy.

Incidence rates of asthma, rhinitis and eczema symptoms and influential factors in young children in Sweden.

AIM: To estimate the incidence rates for asthma, rhinitis and eczema symptoms and to investigate the importance of different influential factors for the incidence of these symptoms. METHODS: The Dampness in Building and Health study commenced in the year 2000 in Värmland, Sweden with a parental questionnaire based on an ISAAC protocol to all children in the age of 1-6 years. Five years later a follow-up questionnaire was sent to the children that were 1-3 years at baseline. In total, 4779 children (response rate = 73%) participated in both surveys and constitute the study population in this cohort study. RESULTS: The 5-year incidence of doctor-diagnosed asthma was 4.9% (95% CI 4.3-5.3), rhinitis was 5.7% (5.0-6.4) and eczema was 13.4% (12.3-14.5). However, incidence rates strongly depend on the health status of the baseline population. Risk factors for incident asthma were male gender and short period of breast-feeding. Allergic symptoms in parents were also a strong risk factor for incident asthma, as well as for rhinitis and eczema. CONCLUSION: When comparing incident rates of asthma between different studies it is important to realize that different definitions of the healthy baseline population will give rise to different incident rates.

Day-care attendance and increased risk for respiratory and allergic symptoms in preschool age.

BACKGROUND: The reported impact of day-care attendance on respiratory and atopic symptoms has varied between studies from different countries. Regarding to the 'hygiene-hypothesis', day-care attendance may lead to less sensitization later in life, but the question still is whether day-care attendance and subsequent exposure to more frequent early infections is a risk or a protection against future allergic disease or asthma (atopic and nonatopic). METHODS: A cross-sectional postal questionnaire was replied by parents of 10,851 children, aged 1-6 years, in the year 2000 in a Swedish region (DBH-phase 1). The questionnaire focused on respiratory and atopic symptoms, the home environment and information on day care of the children. RESULTS: Children in day care were reported to have more symptoms than children in home care: adjusted odds ratio (AOR) for wheezing last 12 months, AOR 1.33 (CI 95%: 1.12-1.58), cough at night apart from colds last 12 months AOR 1.56 (CI: 1.17-2.07), doctor diagnosed asthma AOR 1.23 (CI: 0.88-1.71), rhinitis last 12 months AOR 1.15 (CI: 0.92-1.44), doctor diagnosed hay fever AOR 1.75 (CI: 0.94-3.23), eczema last 12 months, AOR 1.49 (CI: 1.24-1.79), allergic reactions to foods, AOR 1.27 (CI: 1.07-1.52), >6 colds last 12 months of 2.57 (CI: 2.12-3.12) and ear infection ever AOR 2.14 (CI: 1.87-2.45). The increased risks were mainly seen and reached significance in the youngest group of children, aged 1-4 years. Adjusting and stratification for the number of airway infections last year did not change the risk associated with day-care attendance for allergic diseases. CONCLUSIONS: Attending day care was associated with an increased risk of symptoms related to airways infections as well with eczema and allergic reactions to food. No sign of protection from day-care attendance for allergic diseases was found up to 6 years of age. Multiple airway infections and day-care attendance were found to be independently associated with asthma and allergic symptoms.

'Dampness' at home and its association with airway, nose, and skin symptoms among 10,851 preschool children in Sweden: a cross-sectional study.

UNLABELLED: There is convincing epidemiological evidence that 'dampness' in buildings is associated with respiratory effects. In order to identify health-relevant exposures in buildings with 'dampness', the study 'Dampness in Buildings and Health' (DBH) was initiated. In the first step of the study, cross-sectional data on home characteristics including 'dampness' problems, and symptoms in airway, nose, and skin among 10,851 children (1-6 years), were collected by means of a questionnaire to the parents. The prevalence of wheezing during the last 12 months was 18.9% and doctor-diagnosed asthma 5.4%. Rhinitis during the last 12 months was reported for 11.1% of the children and eczema during the last 12 months 18.7%. Gender, allergic symptoms among parents, and age of the child were associated with symptoms. Water leakage was reported in 17.8% of the buildings, condensation on windows in 14.3%, and detached flooring materials in 8.3%. Visible mould or damp spots were reported in only 1.5% of the buildings. The four 'dampness' indices were associated to higher prevalence of symptoms in both crude and adjusted analysis. Furthermore, it was found that the combination of water leakage in the home and PVC as flooring material in the child's or parent's bedroom was associated to higher prevalence of symptoms among children. However, the interpretation of this finding is unclear. The combination of water leakage and PVC may be a proxy, for example, reconstruction because of water damages. PRACTICAL IMPLICATIONS: The study have showed that moisture-related problems in buildings are a risk factor for asthma and allergic symptoms among preschool children. The recommendation to the general public is to remediate damp buildings.

Association between ventilation rates in 390 Swedish homes and allergic symptoms in children.

UNLABELLED: The aim of the study was to test the hypothesis that a low-ventilation rate in homes is associated with an increased prevalence of asthma and allergic symptoms among children. A total of 198 cases (with at least two of three symptoms: wheezing, rhinitis, eczema) and 202 healthy controls, living in 390 homes, were examined by physicians. Ventilation rates were measured by a passive tracer gas method, and inspections were carried out in the homes. About 60% of the multi-family houses and about 80% of the single-family houses did not fulfill the minimum requirement regarding ventilation rate in the Swedish building code (0.5 air changes per hour, ach). Cases had significantly lower ventilation rates than controls and a dose-response relationship was indicated. PRACTICAL IMPLICATIONS: A low-ventilation rate of homes may be a risk factor for allergies among children. Families with allergic children should be given the advice to have good ventilation in the home. In investigations, of associations between environmental factors and allergies, the air change rate in homes has to be considered.

Pet-keeping in early childhood and airway, nose and skin symptoms later in life.

BACKGROUND: It is discussed whether exposure to pets during childhood is a risk or a protective factor for sensitization and allergic symptoms. The aim of this study was to investigate the association between pet-keeping at time of birth and allergic symptoms in airways, nose and skin among young children in Sweden. METHOD: A questionnaire was sent to the parents of 14 077 children (1-6 years), the focus being on allergic symptoms, home environment and other background factors including pet-keeping and avoidance behaviour. The response rate was 79%. RESULTS: Almost one-tenth of the population had got rid of pets because of allergy in the family, and 27.3% reported "avoidance" behaviour towards pets. In a cross-sectional analysis current pet-keeping was "protective", but this may be due to the fact that people avoid exposing their child to something that they believe is a risk factor for allergies. Pet-keeping at the time of birth was associated with "wheezing", "asthma" and "rhinitis on pet-exposure" later in life for children from families with an "avoidance" behaviour, and was not "protective" for other children. There was also an indication of a dose-response relationship between the number of types of furred pets at time of birth and later symptoms in analyses adjusted for avoidance behaviour or current pet-keeping. CONCLUSION: The distribution of pet-keeping in the population is largely explained by avoidance behaviour, meaning that those who have pets mainly are those who can stand them, indicating a "healthy pet-keeping effect".