Viral Exanthem: This is often the most common cause of a maculopapular rash, especially in children and young adults. Viruses such as coxsackievirus, echovirus, and adenovirus can cause widespread rashes.

Allergic Reactions: Medications, foods, and environmental factors can trigger allergic reactions leading to maculopapular rashes. Common culprits include antibiotics, NSAIDs, and certain foods.
Insect Bites or Stings: Reactions to bites or stings from mosquitoes, bed bugs, or other insects can cause maculopapular rashes.
Eczema (Atopic Dermatitis): While typically more localized, eczema can sometimes present with a diffuse maculopapular rash, especially in severe cases or during flare-ups.
Contact Dermatitis: Irritant or allergic contact dermatitis can cause a maculopapular rash, depending on the substance causing the reaction and the area of the body exposed.

Meningococcemia: A life-threatening condition caused by Neisseria meningitidis, which can present with a petechial or maculopapular rash. Early recognition is crucial for survival.
Rocky Mountain Spotted Fever (RMSF): Caused by Rickettsia rickettsii, transmitted by ticks. The rash can be maculopapular and is often accompanied by fever and headache.
Secondary Syphilis: Can cause a diffuse maculopapular rash, among other symptoms. It's critical to consider syphilis in the differential due to its potential for serious complications if left untreated.
Kawasaki Disease: An acute febrile illness of childhood that can present with a maculopapular rash, along with other specific criteria. It's essential to diagnose promptly to prevent cardiac complications.

Pityriasis Rosea: Characterized by a herald patch followed by a widespread, symmetrical maculopapular rash. It's relatively rare and often self-limiting.
Drug-Induced Lupus: Certain medications can induce a lupus-like syndrome, which may include a maculopapular rash among its symptoms.
Sarcoidosis: A systemic granulomatous disease that can rarely present with a maculopapular rash, among other manifestations like lung involvement and lymphadenopathy.
Lymphoma: Some types of lymphoma, particularly cutaneous T-cell lymphoma, can present with skin manifestations, including maculopapular rashes, though this is exceedingly rare as a primary presentation.