Dandruff refers to the shedding of dead skin.  The shedding of dead skin cells is a completely normal process; however, some people tend to have extreme cases of shedding which is also paired with certain skin symptoms such as redness and irritation.  Extreme dandruff can be triggered by varying factors such as stress, excess levels of oil in the scalp, drinking, specific drugs, etc.   Dandruff can be treated with specialized shampoos that will aim to reduce oil levels, redness and itchiness.  If a specialized shampoo does not reduce the level of dandruff then there are other topical and oral treatments that can be pursued.