Two weeks ago I forgot to take my watch off when I went to bed. In the morning I noticed a large area of redness on my left lower chest area. Two days later the redness became blistered and incredibly painful. Today, two weeks later, it looks like an ulcer gone very bad, it still hurts like the dickens, but I think it's getting better. So, after 46 years, I have developed a sensitivity to nickle. The watch strap is stainless steel, but the little safety clasp is nickel. The Dr. said It will take up to 8 weeks to go away completely, and will leave a scar. He also said nickle sensitivity can be more irritating to skin than poison ivy. Nice.