Table 2.

Associations between carpet use and adverse health outcomes.

Authors [Reference]	Type of Study	Results
Norbäck et al. [1].	Longitudinal. Questionnaire. (Initial cross-sectional study with self-reporting of symptoms followed by later questionnaire).	Personnel in schools with wall-to-wall carpet reported increased prevalence of eye and airway symptoms, face rashes, headache and abnormal tiredness compared with those in schools with hard floors. Removal of carpets caused several symptoms to decrease. Frequency of airway symptoms remained increased in the carpet group.
Norbäck et al. [2]	Longitudinal study. A four year study among personnel in six primary schools.	Chronic SBS was related to VOC, previous wall to wall carpeting in the schools, hyperreactivity, and psychosocial factors.
Skov et al. [3]	Cross sectional (self-reported). 2369 office workers in 14 buildings, where indoor climate measurements were made, filled out a questionnaire.	Floor covering, the shelf factor and the fleece factor were among several factors associated with the prevalence of symptoms (work-related mucosal irritation and work related general symptoms).
Wargocki et al. [23]	Reversible intervention study. Experimental study with cross-over design. Persons unaware of intervention were exposed once with the pollution source present and once without the pollution source. Self-reporting of symptoms and evaluation of task performance.	Pollution source was a 20 years old carpet. Removal of pollution source resulted in increased satisfaction with perceived indoor air, reduced prevalence of headaches and significantly faster typing of text. Reducing the pollution load was effective in improving comfort, health and productivity.
Wargocki et al. [24]	Reversible intervention study. Experimental study with a cross-over design. Persons unaware of the intervention. Self-reporting of symptoms and evaluation of task performance.	Carpets used as pollution source. Overall productivity increased with increased ventilation. Results show that maintaining good indoor air quality by controlling indoor pollution sources and ensuring adequate ventilation important for comfort, health and productivity.
Wargocki et al. [25]	Reversible intervention study. Subjective assessments of perceived air quality, intensity of sick building syndrome symptoms and performance of office work.	Removing the pollution source improved the perceived air quality, decreased the perceived dryness of air and the severity of headaches, and increased typing performance.
Bluyssen et al. [26]	Self-reported (Cross sectional study).	An increase in adverse health effects was observed in offices where carpet was the main type of floor covering.
Jaakkola et al. [27]	Cross sectional. (Population-based incident case-control study)	The risk of asthma was related to the presence of plastic wall materials and wall-to-wall carpet at work, the latter in particular in the presence of mold problems (adjusted OR = 4.64, 95% CI: 1.11, 19.4).
Chen et al. [28]	A 1:2 matched case-control study. Self-reported.	Cockroaches, carpet, pets, and in-utero exposures to ETS affected the timing of early-onset asthma.
Ekici et al. [29]	Retrospectiv cross sectional. Parents and grandparents of schoolchildren were asked to answer questionnaires about respiratory system-related symptoms and characteristics in the children.	Childhood respiratory infections associated with increased risk of asthma, chronic bronchitis and chronic cough. Several factors including wall-to-wall carpets were associated with increased risk of frequent childhood respiratory infections.
Ferry et al. [30]	Longitudinal. Exposures to 17 environmental factors before the age of two were reported retrospectively.	Individuals with early childhood asthma more likely to have lived in a house with carpet and more likely to report suffering a serious chest illness before the age of two compared to those with later asthma onset. Carpet exposure and suffering a serious chest illness concurrently before age two increased the individual risk even more.
Vicendese et al. [31]	Hospital-based case-control study.	Carpeted floors in the bedroom associated with increase in asthma readmissions (OR =  4.07, 95% CI 1.03–16.06).
Herr et al. [32]	Longitudinal (Birth cohort). Data on wheezing disorders, medical visits and medications, as well as biological markers of atopy, were collected at 18 months.	Prevalence of wheeze was influenced by several factors where carpet covered floor in the child’s bedroom was one.
Liu et al. [33]	Cross-sectional study.	Bedroom carpets were one of several indoor factors associated with higher prevalence of respiratory symptoms.
Tsai et al. [34]	Genetic analysis and questionnaire about children’s exposure and disease status.	Genetic variation in the IL-13 gene affects health outcomes in the airways. This study indicated that variations in the IL-13 gene could be linked to asthma in children and that asthma disease was related to carpet use.
Zock et al. [35]	Housing data obtained by an interviewer-led questionnaire. Associations between housing data and asthma (based on symptoms the last year) as well as bronchial responsiveness were evaluated.	Carpets and rugs in the bedroom were related to less bronchial responsiveness and fewer asthma symptoms.
Behrens et al. [36]	Data from two cross sectional surveys 5 years apart.	Carpets were inversely associated with adverse respiratory conditions but not when the analysis was restricted to individuals with no report on carpet avoidance due to a history of atopic disease.
Skorge et al. [37]	Self-reported (Cross sectional study).	Wall to wall carpets in the bedroom was negatively associated with cough with phlegm, chronic cough, and attacks of dyspnoea.
Mommers et al. [38]	Nested case-control study. Part of a longitudinal study in children on respiratory health and indoor environment.	A negative association between asthma symptoms and wall-to-wall carpets was observed
Al-Zahrani et al. [39]	Cross sectional study	Carpets in the bedroom were among several factors that did not appear related to the extent of asthma control.
Voute et al. [40]	Longitudinal. Participating children had peak-flow measurements three times a day for a 1-month period. Concurrently, the parents recorded respiratory symptoms and medication use daily.	Peak-flow variability in asthmatic children not related to wall-to-wall carpeting on classroom floors.
Jaakkola et al. [41]	Cross sectional.	Risk of current asthma, wheezing, and allergy in Russian children were related to recent renovation and the installation of materials with potential chemical emissions. This included new linoleum flooring and synthetic carpeting, particleboard which were determinants of one or several of the adverse health outcomes.
Herberth et al. [42]	Blood sampling, inflammatory markers. Within a birth cohort study, blood samples of 6 year old children were analysed for concentration of inflammatory markers.	Increased levels of inflammatory markers were related to renovation activities, in particular, new floor covering. Among floor covering materials only wall-to-wall carpets were associated with elevated IL-8 and Monocyte Chemoattractant Protein-1 (MCP-1) levels.
Ebbehøj et al. [43]	Intervention, cohort.	Workers developed skin and/or airway problems after renewal of offices (new furniture and carpets). Removal of carpets significantly improved symptoms. Workers were examined in 2009 and re-examined in 2013. Chemicals from glued carpets suspected as trigger.
Allermann et al. [44]	In vitro study. The inflammatory potency of floor dust was measured as interleukin-8 secretion from the lung epithelial cell line A549 after exposure to dust.	Carpet flooring may act as a “sink” for microorganisms resulting in a higher inflammatory potency of floor dust