Unkind as it may seem for Mulligan to say that “The unclean bard makes a point of washing once a month,” he is actually being generous to Stephen, or ignorant of the true magnitude of his problem. Stephen has not had a bath for eight months, because he has a morbid fear of water.
Ithaca explains "That he was hydrophobe, hating
partial contact by immersion or total by submersion in cold
water (his last bath having taken place in the month of
October of the preceding year), disliking the aqueous
substances of glass and crystal, distrusting aquacities of
thought and language."
The last proclivity may be assigned to Stephen’s Jesuitical love of intellectual clarity, but the phobia dates to a single event narrated in A Portrait. As a very young boy (probably age 6), and new to Clongowes Wood College, he was pushed by an older boy into “the square ditch,” a cesspool for a privy used by the boys in the dormitory. The water was “cold and slimy,” another boy “had once seen a big rat jump into the scum,” and Stephen is soon sent to the infirmary with a severe infection that makes him wonder whether he will die. Now, at age 22, he still dreads the water, as he acknowledges in Proteus when he thinks of "my fear" in contrast to Mulligan's aquatic heroism.