Viral Exanthem: This is a common cause of a maculopapular rash in adults, often accompanied by systemic symptoms such as full body aches. The rash's description and the patient's symptoms align with a viral etiology, which could include infections like parvovirus B19, among others.

Drug Reaction: Many medications can cause a maculopapular rash, and given the widespread nature of the rash and the absence of itch or pain, a drug reaction should be considered, especially if the patient has recently started new medications.
Allergic Contact Dermatitis: Although the rash is not itchy, which is unusual for allergic contact dermatitis, it's still a possibility, especially if the patient has been exposed to new substances or products.
Infectious Mononucleosis: Caused by Epstein-Barr virus, this condition can present with a rash, fever, and body aches, although the rash is not always present.

Toxic Shock Syndrome: Although rare, this condition is life-threatening and can present with a rash, fever, and body aches. It's crucial to consider this diagnosis, especially if the patient shows signs of systemic illness.
Stevens-Johnson Syndrome/Toxic Epidermal Necrolysis: These are severe skin conditions usually triggered by medications or infections. They can be life-threatening and require immediate medical attention.
Meningococcemia: This bacterial infection can cause a rash and is life-threatening. The rash can initially appear as a maculopapular rash before progressing to petechiae or purpura.

Secondary Syphilis: This can cause a variety of rashes, including a maculopapular rash, and is often accompanied by systemic symptoms.
Kawasaki Disease: Although more common in children, Kawasaki disease can occur in adults and presents with fever, rash, and other systemic symptoms.
Erythema Multiforme: This condition can cause a target-like rash but can also present with a maculopapular appearance. It's often associated with infections or medications.