There is provided a cosmetic additive in which the cosmetic obtained by mixing has excellent transparency, and good spread and feeling of use during application, and stickiness when dried can be suppressed, and a cosmetic containing the additive. A cosmetic additive containing cellulose fibers having an average fiber diameter (D) of 0.001 to 0.05 μm, and a ratio (L/D) of average fiber length (L) to average fiber diameter (D) of 5 to 500; and a cosmetic containing the cosmetic additive.