system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: What is dandruff and why does it only appear on my head?
gpt
People often confuse little white flakes on the shoulder as dandruff. Thats not. Thats just dry skin. Dry skin falls off of all of your body. Your head and shoulders are visible and your shoulders provide a nice landing spot to show case some dead skin cells.

Dandruff is a totally different animal. Large yellow greasy flakes fall off. The hair is greasier than normal. 

Shampoo likes to play off normal skin flakes as dandruff to sell product.