Hair holder and hair treatment method using same

A hair holder including a tubular body which has:

• a first opening located at one end;
• and a second opening located at the other end, and which is configured to allow a lock of hair to be inserted from the first opening toward the second opening and to be capable of being rolled up, the tubular body having a longitudinal direction and a width direction that is orthogonal to the longitudinal direction,
• wherein the tubular body has two sheets that form outer surfaces, and
• at least one of the two sheets is formed of a color-changeable sheet that satisfies conditions (1) and (2) below:
• (1) an L* value in an L*a*b* color coordinate space is 90 or less;
• and
• (2) a color difference ΔE*ab value in the L*a*b* color coordinate space between before and after impregnation with a standard hair treatment agent is 1.0 or greater, the standard hair treatment agent containing ammonium thioglycolate in an amount of 6 mass %, ammonium hydrogencarbonate in an amount of 2 mass %, and disodium edetate in an amount of 0.5 mass %, the balance being water, and the standard hair treatment agent being adjusted to a pH of 8.4 at 20° C. using a 28 mass % aqueous solution of ammonia, and
• wherein said color-changeable sheet contains therein a color material that is kneaded into a resin that constitutes raw material fibers of said color changeable sheet, and wherein the color material contains an acid-base indicator, a dye, a pigment or a combination thereof.