Boils are infections occurring in the hair follicle or the oil glands. When the pores get clogged, the dirt and oil trapped inside become the breeding ground for bacteria. First, the skin turns red after which a tender lump develops in the area. After about a week, the infected area forms a bigger lump and starts accumulating pus inside it. Boils usually occur in areas such as buttocks, armpits, face, neck, shoulders and sometimes eyelids. The ones occurring in the eyelid are called sty or stye. If the boils occur in a cluster, the condition is known as a carbuncle.