Metal-induced allergic contact dermatitis, particularly nickel, affects over 10% of the general population. Herein, chitosan-glycerol gel as protective barrier formulation was synthesized by neutralization reaction with an aim to reduce metal-ion diffusion into the skin to prevent allergy. Active functional groups in chitosan-glycerol gel were able to capture allergenic metal ions present in artificial sweat solution. The efficacy of the barrier formulation against nickel-ion penetration was evaluated ex vivo using pig skin. We found that the percutaneous absorption of nickel ion reduced by ∼98% when chitosan-glycerol gel was used as a barrier formulation.