Chitosan-based nail formulations are useful to treat nail inflammatory diseases like psoriasis, atopic dermatitis and lichen planus. The chitosan is normally in the form of an amino-polysaccharide derivative, preferably water soluble, such as hydroxypropyl chitosan. The formulation may be a nail lacquer, a spray, a cream, an ointment, a gel, a lotion or a foam and may have a content in chitosan, chitosan derivative or a salt thereof from 0.1 to 25 wt. % with respect to the total weight of the formulation.