When the Torah was translated into English, the Hebrew word makkah was translated as plague. In the modern lexicon, however, the term plague often brings to mind the hideous Black Plague that decimated Europe in the Middle Ages. While the ten makkot spread across Egypt with the speed of a devastating contagion, the only plague to manifest as a medical condition was the sixth plague: boils. Of course, it would only be fair to note that the "plagues" of frogs and the lice (plagues 2 and 3) were extremely physically uncomfortable for the Egyptians.
The plague of boils is unique in other ways, for it appears to have also been the final blow to the once powerful Egyptian magicians:
"And they [Moses and Aaron] took soot from the furnace, and stood before Pharaoh; and Moses threw it heavenward; and it became boils breaking out into blisters upon man and upon beast. And the magicians could not stand before Moses because of the boils; for the boils were upon the magicians, and upon all the Egyptians" (Exodus 9:10-11).
During the makkah of lice, the magicians had finally admitted that this particular plague was a magical feat that they could not replicate and had even acknowledged God's power: "And the magicians did so with their enchantments to bring forth lice, but they could not: so there were lice upon man, and upon beast. Then the magicians said to Pharaoh, 'This is the finger of God'" (Exodus 8:14-15).
During the plague of boils, the magicians were so personally affected by the boils that they could not even stand in Moses' presence when he appeared before Pharaoh. It is interesting to note that now, with the complete and total defeat of the magicians, it was God who "hardened the heart of Pharaoh" (Exodus 9:12).