Plan Sésame (PS) is a user fee exemption policy launched in 2006 to provide free access to health services to Senegalese citizens aged 60 and over. Analysis of a large household survey evaluating PS echoes findings of other studies showing that user fee removal can be highly inequitable. 34 semi-structured interviews and 19 focus group discussions with people aged 60 and over were conducted in four regions in Senegal (Dakar, Diourbel, Matam and Tambacounda) over a period of six months during 2012. They were analysed to identify underlying causes of exclusion from/inclusion in PS and triangulated with the household survey. The results point to three steps at which exclusion occurs: (i) not being informed about PS; (ii) not perceiving a need to use health services under PS; and (iii) inability to access health services under PS, despite having the information and perceived need. We identify lay explanations for exclusion at these different steps. Some lay explanations point to social exclusion, defined as unequal power relations. For example, poor access to PS was seen to be caused by corruption, patronage, poverty, lack of social support, internalised discrimination and adverse incorporation. Other lay explanations do not point to social exclusion, for example: poor implementation; inadequate funding; high population demand; incompetent bureaucracy; and PS as a favour or moral obligation to friends or family. Within a critical realist paradigm, we interpret these lay explanations as empirical evidence for the presence of the following hidden underlying causal mechanisms: lacking capabilities; mobilisation of institutional bias; and social closure. However, social constructionist perspectives lead us to critique this paradigm by drawing attention to contested health, wellbeing and corruption discourses. These differences in interpretation lead to subsequent differential policy recommendations. This demonstrates the need for the adoption of a “multi-epistemological” perspective in studies of health inequity and social exclusion.