A boil starts as a hard, red, painful lump usually less than an inch in size. Over the next few days, the lump becomes softer, larger, and more painful. Soon a pocket of pus forms on the top of the boil. Signs of a severe infection are
- the skin around the boil becomes red, painful, and swollen;
- more boils may appear around the original one;
- a fever develops;
- the lymph nodes in the area become swollen.