1,3-Butylene glycol (1,3-BG) is widely used in cosmetics, including low-irritant skin care products and topical medicaments, as an excellent and low-irritation humectant. We report a case of allergic contact dermatitis caused by 1,3-BG. A 28-year-old woman suffered from an itchy erythematous eruption on her face. By 2 days of closed patch testing, her own cosmetics and many of the hypo-irritant skin care products showed positive results. A second patch testing showed positive reaction to 1,3-BG (1% and 5%). 1,3-BG was a common component in most of the products that had elicited a positive reaction in the first patch testing. Although allergic contact dermatitis due to 1,3-BG is not so common, we have to consider 1,3-BG as a possible contact allergen in the patients presenting with allergic contact dermatitis due to various cosmetics.