As WebMD points out, rashes specific to the torso can be caused by shingles, pityriasis rosea and heat rash. However, as HowStuffWorks explains, some rashes appear all over the body, including on the torso. These include rashes due to eczema, ringworm, hives, contact dermatitis, psoriasis, acne and allergic reactions.
According to the Mayo Clinic, shingles most commonly manifests as a rash that wraps around one side of the torso and buttocks, though it can also appear on other areas of the body. Shingles is an outbreak of the varicella-zoster virus and typically only occurs in people who experienced chickenpox as a child. A shingles rash is a series of raised blisters that burn and itch. An attack of shingles typically lasts two weeks but can continue for years.
Pityriasis rosea also occurs primarily on the torso, as the Mayo Clinic points out. This rash begins as a single spot of up to 4 inches that then spreads out in a Christmas-tree shape, leading to its nickname as the Christmas-tree rash. Pityriasis rosea is probably caused by a virus, and its main symptom is itching.
According to the Mayo Clinic, heat rash most often occurs when tight-fitting or overly warm clothing obstructs the free flow of sweat from the body. It can either manifest as small, red bumps that sting or as fluid-filled bumps that show no other symptoms. Avoiding heat and wearing loose-fitting clothing typically helps heat rash clear up on its own.