An interesting discovery about the content of tears was made by Dr. William H. Frey II, a biochemist at the St. Paul-Ramsey Medical Center in Minnesota. He and his team analyzed two types of tears: the emotional ones (crying when emotionally upset and stressed) and the ones arising from irritants (such as crying from onions). They found that emotional tears contained more of the protein-based hormones, prolactin, adrenocorticotropic hormone, and leucine enkephalin (natural painkiller), all of which are produced by our body when under stress.
I encourage my clients to let the tears out instead of holding them in. They serve a purpose.