The narrator describes Dr. Jekyll as
a large, well-made, smooth-faced man of fifty, with something of a stylish cast perhaps, but every mark of capacity and kindness—you could see by his looks that he cherished for Mr. Utterson a sincere and warm affection.
In contrast, Mr. Enfield tells Mr. Utterson that he "had taken a loathing" to Mr. Hyde on his very first sight of the man:
But the doctor’s case was what struck me. He was the usual cut and dry apothecary, of no particular age and colour, with a strong Edinburgh accent and about as emotional as a bagpipe. Well, sir, he was like the rest of us; every time he looked at my prisoner, I saw that Sawbones turn sick and white with desire to kill him. I knew what was in his mind, just as he knew what was in mine . . .
Even more than that, Enfield describes Hyde as possessing a "black sneering coolness" and "carrying it off, sir, really like Satan." While Jekyll is kind, handsome, and warm, Hyde is cruel, odious, and unfeeling. Jekyll enjoys people and their company, especially the company of people he cares for (like Utterson), but Hyde seems to care for nothing and no one but himself. In fact, he is so hateful that he inspires the doctor—a man who has taken an oath to do no harm—to seem to want to murder him.
Further, after Utterson meets Hyde himself, the narrator describes Hyde as
pale and dwarfish, he gave an impression of deformity without any nameable malformation, he had a displeasing smile, he had borne himself to the lawyer with a sort of murderous mixture of timidity and boldness, and he spoke with a husky, whispering and somewhat broken voice; all these were points against him, but not all of these together could explain the hitherto unknown disgust, loathing and fear with which Mr. Utterson regarded him.
Jekyll, of course, is described as being rather tall and handsome. Hyde seems cramped and deformed, by contrast. He seems incredibly unnatural, which, of course, he is, and this sense of his unnaturalness seems to impact everyone who meets him. Human beings are by nature, in this text, comprised of both good and bad parts—capable of being both kind and wicked—and yet this person is only bad and wicked. People seem to sense this right away.