Contact dermatitis is a red, itchy rash caused by direct contact with a substance or an allergic reaction to it. The rash isn’t contagious or life-threatening, but it can be very uncomfortable. Many substances can cause such reactions, including soaps, cosmetics, fragrances, jewelry and plants. To treat contact dermatitis successfully, you need to identify and avoid the cause of your reaction. If you can avoid the offending substance, the rash usually clears up in two to four weeks.