Blackheads are dark formations on the skin due to an accumulated mixture of oil and cells in a blocked skin pore. Whiteheads are small flesh-or white-colored bumps due to skin pore blockage. Cysts are closed sacs beneath the skin or deeper that contain fluid or semisolid substances. The areas of the skin that are most susceptible to acne are those areas that contain the largest number of oil glands.
For example, it is estimated that there are 2,000 oil glands per square inch on the forehead alone. The face, chest, shoulders, and back are the areas with the highest population of oil glands.
Acne commonly occurs in people between their teenage years and their 20s. However, it is not restricted to this age. Older adults and children can also have acne.