Human tears are of three types and have different chemical composition

There are three types of human tears: basal, reflex and emotional, which differ in their chemical composition. Basal tear allocated continuously in small quantities, wetting cornea and protecting eyes from dust and bacteria.

The second type of tears - a reaction to stimuli, such as foreign particles, evaporation from the bow or tear gas. The third type are the tears of emotions, both negative and positive - they stand out when a person cries. It contains specific hormones prolactin and ACTH in a much higher concentration compared to basal reflex and tears that can be discerned even by smell.

via factroom.ru