What are boils and carbuncles?

A boil, also known as a furuncle, is a single hair follicle which has become infected, notes WebMD. The follicle fills with pus and becomes red, inflamed and painful. A carbuncle is a group of several boils that form under the skin and connect to form one larger infected area.

Boils and carbuncles are usually caused by staphylococcus aureus bacteria, or staph, notes Drugs.com. One boil can be left to heal alone if it is kept clean. When popped, it becomes contagious and can spread, either to other areas on the infected person or to other people, according to WebMD. Once a carbuncle has formed, medical treatment is required to promote healing, manage complications and reduce scarring, notes Drugs.com.