Tinea corporis (Ringworm): This is the most likely diagnosis because the question specifically mentions a rash that looks like ringworm. Tinea corporis is a common fungal infection characterized by circular, itchy, and red patches on the skin.

Nummular dermatitis: This condition presents with coin-shaped patches of eczema, which can resemble ringworm. It's often seen in individuals with a history of atopic dermatitis.
Granuloma annulare: A benign skin condition that forms a ring-shaped lesion, typically on the hands or feet. It's more common in children and young adults.
Pityriasis rosea: Although it doesn't always present in a ring-like fashion, some cases can mimic ringworm, especially in the early stages. It's characterized by a herald patch followed by a secondary eruption of oval-shaped lesions.

Lyme disease (Erythema migrans): The initial stage of Lyme disease can present with a distinctive "bull's-eye" rash, which might be mistaken for ringworm. Missing this diagnosis can lead to serious complications if left untreated.
Erythema multiforme: A skin condition characterized by target-like lesions, which can sometimes appear ring-like. It can be associated with infections, medications, or other medical conditions, and requires prompt recognition and treatment.

Sarcoidosis: A systemic disease that can cause skin lesions, including those that might resemble ringworm. It's less common and typically presents with other systemic symptoms.
Cutaneous leishmaniasis: In some cases, this parasitic infection can cause skin lesions that might be mistaken for ringworm, especially in travelers to endemic areas.
Mycobacterial infections (e.g., cutaneous tuberculosis): These can cause a variety of skin lesions, including some that might resemble ringworm. They are less common and often associated with systemic symptoms or immunocompromised states.