In this paper, we are concerned with a mathematical model of secondhand smoker.
The model is biologically meaningful and mathematically well posed. The reproductive number R0 is determined from the model, and it measures the average number of
secondary cases generated by a single primary case in a fully susceptible population. If
R0 < 1, the smoking-free equilibrium point is stable, and if R0 > 1, endemic equilibrium
point is unstable. We also provide numerical simulation to show stability of equilibrium
points. In addition, sensitivity analysis of parameters involving in the dynamic system
of the proposed model has been included. The parameters involving in reproductive
number measure the relative change in R0 when the value of the parameter changes.