Abstract: It is an object of the present invention to provide fibers, a clothing fabric, and underwear which can maintain excellent cool contact feeling, texture, and pleasant feeling and can suppress fiber yellowing and reddening in distribution process or during in use. The present invention provides fibers containing a thermoplastic elastomer, an acidic compound, and a phosphorus antioxidant, wherein the acidic compound is a styrene-maleic anhydride copolymer or an acid anhydride and the acidic compound is contained in an amount of 0.1 parts by weight or more per 100 parts by weight of the thermoplastic elastomer.