Furuncles, commonly known as boils, are painful, pus-filled bumps that form under the skin when hair follicles become infected. They are usually caused by bacteria, particularly Staphylococcus aureus, and can occur anywhere on the body, though they are most common in areas where friction occurs, such as the armpits and thighs. These infections often start as red, swollen lumps and can grow larger over time. Treatment typically involves warm compresses to promote drainage, and in some cases, a healthcare provider may need to drain the boil. Maintaining good hygiene can help prevent furuncles from developing.