Blackheads are small, dark spots that appear on the skin, typically on the face, nose, chest, or back. They form when pores become clogged with excess oil, dead skin cells, and debris. Unlike whiteheads, which are closed, blackheads remain open, allowing the trapped material to oxidize upon exposure to air, turning it dark in color. They are a common type of acne and can be caused by factors such as hormonal changes, poor skin care, or excessive oil production.