Boils are primarily caused by infection of a hair follicle or oil gland by bacteria, most commonly Staphylococcus aureus (staph bacteria), which is frequently found on the skin and inside the nose

. The infection usually begins when bacteria enter the skin through small breaks such as cuts, insect bites, or other skin injuries, allowing the bacteria to invade deeper tissues

. The body’s immune response sends white blood cells to fight the infection, resulting in pus formation under the skin, which creates the painful, swollen lump known as a boil

. Boils often develop in areas where hair follicles are abundant and where skin rubs together or sweats, such as the face, neck, armpits, buttocks, thighs, and groin

. Certain factors increase the risk of developing boils, including:

• Having a weakened immune system (due to conditions like diabetes, HIV, or other illnesses)

• Poor hygiene or skin conditions like eczema that break the skin barrier

• Close contact with someone who has a staph infection

• Obesity and poor nutrition

Boils can sometimes recur, especially if a person is a carrier of staph bacteria or has an underlying condition that impairs the immune system

. In summary, boils are caused by bacterial infection (mainly Staphylococcus aureus) of hair follicles or oil glands, facilitated by breaks in the skin and influenced by individual risk factors such as immune status and hygiene