General Halleck's itchy elbows

General Henry Wager Halleck served as general-in-chief and chief of staff of the Federal army from 1862-1865. Unpopular with troops as well as with many members of the Lincoln administration, he was a particular source of irritation to Secretary of Navy Gideon Welles. In his posthumously-published diary of the war years, Welles viciously criticized Halleck for his failings as army commander. Welles also derided Halleck's personality and personal appearance. Welles found the general's habitual elbow-scratching annoying enough to mention it in five separate diary entries. This depiction of Halleck ceaselessly, nervously scratching his elbows has entered Civil War folklore. Why did Halleck scratch his elbows? Two possibilities exist. Either he did so compulsively, as a nervous habit, or he was scratching an itch. In this paper, I present a speculative argument that Halleck may have had a skin disease, possibly atopic dermatitis, and that this may have contributed to or have been the sole cause of his elbow scratching.