Overcrowding and Hazardous Dwelling Condition Characteristics: A Systematic Search and Scoping Review of Relevance for Health.

Crowding in dwellings is an important public health issue. We hypothesize that overcrowding may cause indirect health effects by adversely affecting the dwelling itself, for example, by increasing dampness leading to mold. We therefore performed a systematic search and a scoping review on overcrowding leading to dwelling condition characteristics of relevance for health. A literature search was performed using the PubMed and Scopus databases up to 5 March 2021. The search yielded 100 records with relevant information. We found that overcrowding is defined in numerous ways and often address "socially deprived" populations. Six studies report associations of overcrowding with at least one dwelling condition characteristic, namely lead, cadmium, microorganism distribution, dust mite and cockroach allergens in dust, cockroach infestation, peeling paint, and mold. One of the studies reports associations between several characteristics, e.g., association of mold with cleanliness and rodent infestation, and points out the common use of pesticides. Additional characteristics were extracted from the remaining 94 records, without data on statistical associations with overcrowding. Our review suggests that multiple potentially hazardous dwelling condition characteristics often coincide in overcrowded dwellings. The epidemiological attribution of health effects to any characteristic is therefore difficult. Causal relationships are even more difficult to establish, as overcrowding is also associated with a range of social and other circumstances that may affect health. The complexity should be considered by scientists and practitioners dealing with overcrowding in dwellings.