The level of melatonin in the saliva is about 30% of that in blood, recognized to present the free, unbound plasma melatonin levels.228 Like blood melatonin, salivary melatonin is an indicator of the circadian phase.228 Besides, the detection and quantification of daytime salivary melatonin content can positively reflect the levels of some depression-related inflammatory markers, such as CCL2/MCP-1, CCL3/MPI-1α, and VEGF-A.229 Yvan et al. has found a positive correlation between salivary melatonin levels and urinary excretion of 6-sulphatoxymelaton in children. Here, CCL2 is linked to major depressive disorder.