Papules: These are small, raised bumps that indicate inflammation is occurring in hair follicles.
Pustules: Larger than papules, these red, tender bumps have white pus at their tips and are a sign of a more advanced, deeper inflammation.
Nodules: One of the most painful forms of acne, these bumps remain below the surface of the skin and are large and solid. They develop when buildup occurs deep within hair follicles that are severely clogged.
Cysts: Painful, pus-filled lumps that form beneath the skin, and that present an increased risk of scarring due to their depth and collagen-destroying potential. You can learn more about how cysts form - and how to treat them - in our article Cystic Acne Agony.