Staphylococcus aureus, a type of bacteria that normally lives on the skin and in the nose, is frequently the cause of boils, according to Mayo Clinic. The bacteria gain entry to the body via a small nick in the skin or via an insect bite.
Boils are skin infections that commonly develop on the face, neck, armpits, shoulders and buttocks, states WebMD. In some cases, an ingrown hair can result in a boil, advises MedicineNet.com. In other cases, a splinter or other object lodged under the skin may cause a boil to develop. Clogged sweat glands that become infected may cause boils related to acne.