Exodus 9:8-12 -- Boils

Exodus 9:8 Then the Lord said to Moses and Aaron, “Take handfuls of furnace soot, and Moses is to throw it toward heaven in the sight of Pharaoh. 9 It will become fine dust over the entire land of Egypt. It will become festering boils on man and beast throughout the land of Egypt.” 10 So they took furnace soot and stood before Pharaoh. Moses threw it toward heaven, and it became festering boils on man and beast. 11 The magicians could not stand before Moses because of the boils, for the boils were on the magicians as well as on all the Egyptians. 12 But the Lord hardened Pharaoh’s heart and he did not listen to them, as the Lord had told Moses.

All the Egyptians had boils, all over their skin.  Their animals did as well.  You may think, but weren't all their animals just killed?  Well, yes and no.  Yes they were all killed during the last plague, but we do not know how much time passed between that plague and this one.  It is possible that the Egyptians acquired some animals in that time.

This plague showed the Egyptians that the God of Israel had control over their health.  The gods of Egypt could not overcome the boils and cure the Egyptians.  The magicians could not even stand before Moses.  They were so covered in boils they did not even attempt to replicate or remove the boils.

In Deuteronomy, the Lord says this:

Deuteronomy 28:15 “But if you do not obey the Lord your God by carefully following all His commands and statutes I am giving you today, all these curses will come and overtake you:

and one punishment is:

Deuteronomy 28:27 “The Lord will afflict you with the boils of Egypt, tumors, a festering rash, and scabies, from which you cannot be cured.

Pharaoh disobeyed God by not letting the people of Israel go, so one of their punishments was the boils on the skin, which they could not heal themselves.