Studies have shown that vaginal touch triggers the brain to release oxytocin.
If steam is setting off this trigger then that would explain reports by steam users of experiencing deeper sleep, enhanced feelings of love and sexual pleasure, increased breastmilk production, a higher state of relaxation, and an overall increase of happiness following vaginal steaming. All of these feelings are associated with the oxytocin hormone.
Sources:
https://www.ncbi.nlm.nih.gov/pubmed/3223304; Vagal afferents from the uterus and cervix provide direct connections to the brainstem;https://www.ncbi.nlm.nih.gov/pubmed/9931352;Increased plasma levels of oxytocin in response to afferent electrical stimulation of the sciatic and vagal nerves and in response to touch and pinch in anaesthetized rats. ;https://www.ncbi.nlm.nih.gov/pubmed/3223304;10 Reasons Why Oxytocin is the Most Amazing Molecule in the World;http://io9.gizmodo.com/5925206/10-reasons-why-oxytocin-is-the-most-amazing-molecule-in-the-world;The Orgasmic History of Oxytocin: Love, Lust and Labor https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3183515/