Is dandruff the only cause of visibly flaky scalp?

Most people have met someone who suffers from dandruff if they do not suffer from the condition themselves. At some time or another, we have all encountered someone with the tell-tale white flakes in their hair and on their shoulders, so most of us are familiar with what dandruff looks like.
However, the white lumps or flakes on the shoulders of someone wearing dark clothing do not necessarily indicate a person who suffers from dandruff, because there are other conditions that can cause the skin on the scalp to flake in a similar way.
Some of these conditions might require medical attention or special treatment, so you cannot automatically assume that flaky skin landing on your shoulders immediately tells you that you have dandruff (although as dandruff would be by far the most common cause of flaky skin, it would be the most likely cause).
Learning to recognize these other conditions is a valuable exercise as it should enable you to differentiate between dandruff and something else that might be (or may become) more serious and worthy of medical attention.
Dandruff problems.