When the plugged follicle can no longer hold its contents, it bursts and spills everything onto the nearby skin-sebum, shed skin cells, and bacteria. Lesions or pimples develop as a result of the skin's being irritated. People with acne frequently have a variety of lesions. This lesion is often referred to as a microcomedo because it cannot be seen by the naked eye. If the plugged follicle, or comedo, stays beneath the skin, it is called a closed comedo or whitehead.
Whiteheads usually appear on the skin surface as small, whitish bumps.
A comedo that reaches the surface of the skin and opens up is called a blackhead because it looks black on the skin's surface. This black discoloration is not due to dirt. Both whiteheads and blackheads may stay in the skin for a long time. The exact cause of acne is unknown, but doctors believe it results from several related factors. One important factor is rising hormone levels.