Use of a composition comprising shortened fibers of poly-β-1→4-N-acetylglucosamine (“sNAG nanofibers”) for topical administration for treating inflammatory bowel disease in a human subject having inflammatory bowel disease, such as ulcerative colitis or Crohn’s disease, wherein the sNAG nanofibers comprise 70%, or more than 70%, of N-acetylglucosamine monosaccharides, and wherein (i) more than 50% of the sNAG nanofibers are between 1 to 15 µm in length, or (ii) the sNAG nanofibers are less than about 15 µm in length. Preferably the sNAG nanofibers are of microalgal origin,
