When defining hair and its composition the subject matter can become complex very quickly. This is largely due to the many processes involved. To prevent any confusion we will discuss, in detail, how hair is formed later. Our initial intent is to keep our topics as simple as possible.

Hair occupies space and has weight (mass) and can therefore be characterized as matter. One of the key elements of hair is sulfur. Hair also consists of a fibrous protein called keratin. From these statements one may conclude:

Hair is composed of keratin. Keratin can be defined as a sulfur-rich protein.