A skin condition that occurs when hair follicles plug with oil and dead skin cells. Blackheads are small bumps that appear on your skin due to clogged hair follicles. When these pores are plugged, the dead skin cells in the open pore react with oxygen in the air and turn black, forming a blackhead. Enjoy the videos and music you love, upload original content, and share it all with friends, family, and the world on YouTube. A comedo is a clogged hair follicle (pore) in the skin. Blackhead facts · Blackheads are composed of dried sebum (oil) and dead skin cells.