Systemic Lupus Erythematosus (SLE): This is the most common cause of a malar rash, which is a characteristic "butterfly-shaped" rash across the cheeks and nose. SLE is an autoimmune disease that can affect various parts of the body, including the skin, joints, kidneys, and other organs.

Rosacea: A chronic skin condition characterized by inflammation of the skin on the face, leading to redness, acne-like symptoms, and sometimes a malar rash.
Dermatomyositis: An inflammatory disease that affects the muscles and the skin, causing a distinctive rash on the face, including the malar area, as well as muscle weakness.
Sjögren's Syndrome: An autoimmune disorder that primarily affects the glands that produce tears and saliva, but can also cause skin rashes, including a malar rash.

Lyme Disease: Caused by the bacterium Borrelia burgdorferi, transmitted through the bite of an infected tick. Early stages can present with a distinctive rash (erythema migrans), which, although not typically malar, should be considered due to its serious implications if untreated.
Erythema Multiforme: A skin condition characterized by target lesions, which can sometimes appear as a malar rash. It can be triggered by infections or medications and has a range of severity.

Sarcoidosis: A disease in which granulomas (abnormal masses of inflamed tissue) can form in various parts of the body, including the skin, leading to rashes that could resemble a malar rash.
Polymorphous Light Eruption (PMLE): A skin condition that occurs in response to sunlight, causing a rash that could potentially appear on the face, including the malar area, though it's less common in this specific distribution.