@markyy (yes real doctor). I feel I need to explain a bit. The effect of pressure reduction that stems from crying is not it’s primary function or the cause of crying per se.. it’s simply one of the occurences during the crying episode and one of the ways it can be brought about. Increased bloodflow and vasodilations fosters fluid buildup in the glands which secrete their excess tears/mucus. Crying in itself can be a response to specific physical ain and/or emotional pain and stress and has been shown to not only reduce stress and increase a sense of emotional release, but also a sense of physical well being through the production of endorphins. You could say it’s a sort of self defense mechanism in which the body feels a need for release (think of the body as a steam cooker) and finds the fastest outlet.
Some studier have shown remarkable findings in clinical populations, demonstrating a
beneficial effect of shedding emotional tears on physical health. Saul and Bernstein (1941) and French (1939) found intriguing relationships between crying and course of urticaria (i.e., hives) and asthma, respectively, suggesting that crying reduces the symptoms of these conditions. Kepecs, Robin and Brunner (1951) reported a
relationship between crying and exudation into cantharides blisters in the skin, showing that the inhibition of crying was followed by an initial drop in the exudation rate, later followed by an increase if the inhibition continued. More recently, a study among
patients with rheumatoid arthritis revealed that shedding tears reduces the negative influence of stress on the neuroendocrine and immune responses in peripheral blood (Ishii, Nagashima, Tanno, Nakajima, & Yoshino, 2003), and Kimata (2006) showed that
crying reduced allergic reactions. Furthermore, an experimental rat study (Ilinskii et al., 1985) even suggests that stimulation of the lacrimal gland may have a positive effect on wound healing. However, these intriguing findings need replication. In addition to the question regarding in which conditions crying may be beneficial.
Four potential relevant hypotheses have been formulated concerning the putative underlying mechanisms that might be responsible for the supposed positive
effects of crying.. The first idea, mentioned earlier, is that crying stimulates the activity of the parasympathetic nervous system, which is connected to relaxation and recovery, but also to helplessness and giving-up (Vingerhoets, 1985). Along these lines, Rottenberg, Wilhelm, Gross, and Gotlib (2003) and Hendriks et al. (2007) have demonstrated that crying is indeed associated with a parasympathetic rebound mechanism. Another possible mechanism that has received much attention in the popular media is Frey’s (1985) idea that tears function in the removal of toxic waste products (e.g.,stress hormones), which are released in the blood when we are in distress, which is presumed to result in a better mood and perhaps even better health.
Hope this helps.