Contact Dermatitis: This is a common condition that can start on the legs due to exposure to allergens or irritants and then spread to other areas, including the torso, upon further exposure or through autoeczematization.

Eczema (Atopic Dermatitis): Often starts in childhood but can persist into adulthood, characterized by itchy, inflamed skin that can begin on the legs and spread to the torso.
Psoriasis: An autoimmune condition that speeds up the life cycle of skin cells, causing cells to build up rapidly on the surface of the skin. The lesions can start on the legs and spread to the torso.
Tinea Infections (Ringworm): Fungal infections that can start on the legs and spread to other areas, including the torso, through direct contact or contaminated items.

Meningococcemia: A severe, life-threatening infection caused by Neisseria meningitidis, which can present with a rash that starts on the legs and spreads to the torso. The rash is often accompanied by fever, headache, and other systemic symptoms.
Rocky Mountain Spotted Fever (RMSF): A tick-borne illness caused by Rickettsia rickettsii, characterized by a rash that typically starts on the wrists, ankles, palms, and soles but can spread to the torso, accompanied by fever and headache.
Syphilis (Secondary): Can present with a rash on the palms and soles that may spread to the torso, along with other systemic symptoms like fever, lymphadenopathy, and mucocutaneous lesions.

Kawasaki Disease: Although more common in children, it can rarely occur in adults, presenting with fever, rash, lymphadenopathy, and desquamation of the hands and feet, which might initially appear on the legs.
Sweet Syndrome (Acute Febrile Neutrophilic Dermatosis): Characterized by the sudden onset of fever, leukocytosis, and tender, erythematous skin lesions that can start on the legs and spread to the torso, often associated with underlying systemic diseases or infections.