Normally, the skin renews itself every few weeks. For example, the skin on your scalp falls off in the form of very small flakes so that a new layer of skin can replace the older layer. The flakes that fall off are usually so small that you usually do not notice this occurring. However, sometimes these flakes may clump together to form very large flakes that become clearly visible to the naked eye. This condition is known as dandruff.
It is not clear why some people get dandruff while others do not. Some scientists believe that there is a yeast-like fungus that can make cells in your skin to grow extra fast. These extra skin cells will mix with the oil in your hair and then fall off in large clumps. Dandruff may also occur as a result of having too much oil. The extra oil can clump up the tiny flakes in your hair to make bigger and more visible flakes. If you are going through puberty or do not wash your hair on a regular basis, it is likely that you may get a build-up of hair oil.