Figure 1

Evidence base for increase in non-atopic asthma in the following domains: infections/humidity/dirt (green), history (orange), nutrition (yellow), psychosocial (violet), smoking (blue), pregnancy and perinatal issues (pink), and socio-economic status (brown); evidence not found (grey). Risk factors are displayed as circles of sizes proportional to the number of studies. Digits inside the circles are the relevant reference numbers.