An inflamed area of swelling on the skin. In modern medicine, a "boil" is a pus-filled swelling. It is caused by infectious germs, usually staphylococci. The pus is a mixture of germs and white blood cells, the body’s defense against germs. Although painful, boils usually heal naturally after rupturing or being cut open. A more severe boil with several openings is called a carbuncle. If the infection goes deeper and injures internal organs or tissues, it is called an abscess and can even be fatal.
In the Bible, the word translated as “boil” probably referred to a variety of skin diseases. The sixth plague that God inflicted on Egypt through Moses and Aaron was a plague of boils (Exodus 9:9–11; Deuteronomy 28:27, 35) or blisters. Boils or skin eruptions of a certain type were described in the Mosaic laws about health and cleanliness as one sign of leprosy (Leviticus 13:1–8, 18–23). Job’s “terrible boils from the soles of his feet to the crown of his head” (Job 2:7–8, 12) were probably too widespread to be called boils in the modern sense. He may have had:
Smallpox
Psoriasis
Tubercular leprosy
Some other disease that caused severe itching
King Hezekiah’s boil was probably a group of boils (2 Kings 20:1–7; Isaiah 38:21).