Viral exanthem (e.g., measles, rubella, roseola): This is often the most common cause of maculopapular rash, especially in children, due to the high prevalence of viral infections.

Allergic reactions (e.g., to medications, foods): These are common and can cause a wide range of skin manifestations, including maculopapular rashes.
Contact dermatitis: Direct skin contact with irritants or allergens can lead to a maculopapular rash.
Drug eruptions: Many medications can cause skin reactions, including maculopapular rashes, as an adverse effect.
Insect bites: Reactions to insect bites can sometimes appear as a maculopapular rash.

Meningococcemia: Although less common, this condition can present with a maculopapular rash that progresses to purpura and is life-threatening if not promptly treated.
Rocky Mountain Spotted Fever (RMSF): This tick-borne illness can start with a maculopapular rash and is critical to diagnose early due to its high mortality rate if left untreated.
Secondary Syphilis: The rash of secondary syphilis can be maculopapular and is a crucial diagnosis not to miss due to the implications for public health and the potential for serious complications if untreated.

Kawasaki Disease: An acute febrile illness of childhood that includes a maculopapular rash among its diagnostic criteria, though it's more known for its mucocutaneous lymph node syndrome.
Erythema Infectiosum (Fifth Disease): Caused by parvovirus B19, it presents with a distinctive "slapped-cheek" appearance but can also have a maculopapular component.
Pityriasis Rosea: A skin condition characterized by a herald patch followed by a maculopapular rash, typically on the trunk, in a Christmas tree distribution.