Many patients say they have metal allergies, most commonly belt buckles, metal ornaments (earrings, necklaces, rings, etc.), but it is actually metallic nickel that is at fault. Metal-nickel allergy is clinically divided into 3 phases. Phase 1 is mainly in contact with the site: such as metal belt buckle around the umbilicus triggers dermatitis, bra back buckle in the back triggers dermatitis. Nickel-containing jewelry such as necklaces and earrings can cause dermatitis at the site of wear, and many others. Stage 2 lesions can spread to the surrounding skin as a result of allergens spreading through lymphatic vessels. Stage 3 is hematogenous disseminated dermatitis. Systemic absorption of nickel in nickel-sensitive individuals can cause systemic contact dermatitis, manifesting as sweat pimples, generalized eczema, etc. In addition to the nickel-containing metals that we can see in our daily lives, there are many things that contain nickel that we cannot see, such as the soaps and detergents we commonly use; and some foods such as mushrooms, corn, celery, etc. contain nickel. Due to the wide distribution of nickel, it is difficult to completely avoid exposure and dermatitis can recur. Therefore, patients are reminded to pay attention to the premise of life, once the onset of treatment in a timely manner.