SCAALA investigated the association between asthma prevalence and other allergic diseases, and potential risk factors such as early exposure to infections, environmental, nutritional, immunological, and psychosocial factors. Participants of SCAALA were part of an earlier study that investigated the impact of a sanitation program on the occurrence of childhood diarrhoea. As part of the earlier study, between 1997 and 2003, children aged 0 to 3 years were recruited from 24 areas selected to represent the population without sanitation in Salvador, Brazil, and the children were assessed at baseline and followed up every two weeks for one year. SCAALA involved two follow-up assessments of participants from the earlier study between 2005 and 2006, and again in 2008. The total number of participants recruited into SCAALA was 1,445 children and their mothers, and the children were between the ages of 4 and 12 years.