Mammary intercourse is said by Alex Comfort to produce mutual orgasm in women with sensitive breasts (what Margot Anand terms local orgasms of the breast),[REF][REF] and it was one of the nine substitute exercises for penetrative sexual activities, as detailed in the Paradis Charnels of 1903 [REF].
Since mammary intercourse is a non-penetrative sex act, the risk of passing a sexually transmitted infection (STI) that requires direct contact between the mucous membranes and pre-ejaculate or semen is greatly reduced.