The term morbilliform refers to a rash that looks like measles. The rash consists of macular lesions that are red and usually 2–10 mm in diameter but may be confluent in places. A morbilliform rash is a rose-red flat (macular) or slightly elevated (maculopapular) eruption, showing circular or elliptical lesions varying in diameter from 1 to 3 mm, with healthy-looking skin intervening.
Patients with measles will have the rash but there are other syndromes and infections that will display the same symptom such as patients with Kawasaki disease, meningococcal petechiae or Waterhouse-Friderichsen syndrome, Dengue, Roseola, congenital syphilis, rubella, Echovirus 9, drug hypersensitivity reactions (in particular with certain classes of antiretroviral drugs, such as abacavir and nevirapine, and also the antiepileptic drug phenytoin), or other conditions may also have a morbilliform rash. It is usually present in drug reaction with eosinophilia and systemic symptoms (DRESS syndrome) following a prodrome of fever, malaise, throat pain with dysphagia, and itching. It has also been mentioned as a possible manifestation of onset or recovery from COVID-19.