Contact Dermatitis: This is often the most common cause of a rash on the torso, resulting from an allergic reaction or irritation to substances like soaps, detergents, or plants. The rash typically appears as red, itchy, and blistered skin.

Eczema (Atopic Dermatitis): Characterized by dry, itchy, and inflamed skin, eczema can appear anywhere on the body, including the torso. It's a chronic condition with periods of flare-ups.
Psoriasis: An autoimmune condition leading to thick, scaly, red patches on the skin, often on the torso. It can be itchy and painful.
Fungal Infections (Tinea Corporis): Also known as ringworm, this fungal infection causes a ring-shaped rash on the torso or other parts of the body. It's contagious and can be itchy.
Viral Exanthems: Various viral infections can cause rashes on the torso, such as measles, chickenpox, or roseola. These are often accompanied by fever and other systemic symptoms.

Lyme Disease: Caused by a tick bite, Lyme disease can initially present with a distinctive "bull's-eye" rash (erythema migrans) on the torso or other areas. Missing this diagnosis can lead to serious complications if not treated promptly.
Meningococcemia: A severe infection caused by Neisseria meningitidis, which can present with a rash on the torso among other symptoms. It's life-threatening and requires immediate medical attention.
Stevens-Johnson Syndrome/Toxic Epidermal Necrolysis: These are severe skin conditions usually triggered by medications or infections, leading to widespread skin necrosis and detachment. They are medical emergencies.

Pityriasis Rosea: A rare skin condition characterized by a rash that starts with a single, large spot (herald patch) followed by smaller spots, typically on the torso. The cause is unknown, but it's thought to be related to viral infections.
Kawasaki Disease: Although more common in children, Kawasaki disease can cause a rash on the torso along with fever, swollen lymph nodes, and other symptoms. It affects the blood vessels and can lead to serious heart complications if not treated.
Sarcoidosis: A condition where inflammatory cells form lumps known as granulomas in various parts of the body, including the skin. Skin symptoms can include rashes on the torso, among other areas.