Milia are white, enclosed keratin-filled cysts that contain sebum, dead skin cells and bacteria, which form a hard ball beneath the outer layer of the skin.

• A. Whitehead
• B. Blackhead
• C. Steatoma
• D. Milia

Answer: (D)

Milia are tiny, white, enclosed cysts that form when keratin becomes trapped beneath the outer layer of the skin, creating a hard, white bump just under the surface. The description in the question—white, enclosed keratin-filled cysts forming a hard ball beneath the skin—fits milia perfectly, since these bumps are keratin-filled and sit beneath the epidermis rather than being oil-filled or open to the surface. This distinguishes them from whiteheads or blackheads, which are clogged follicles filled with sebum and dead skin cells, and from steatomas, which are sebaceous cysts filled with oil.