Butterfly rash: A red, flat facial rash over the bridge of the nose. Many patients with systemic lupus erythematosus (SLE) develop this characteristic rash. Because of its shape, it is frequently referred to as the "butterfly rash" of lupus.
The butterfly rash of lupus is typically painless and does not itch. Along with inflammation in other organs, the butterfly rash of lupus can be precipitated or worsened by exposure to sunlight, a condition called photosensitivity. The photosensitivity can be accompanied by a worsening of inflammation throughout the body, causing a "flare" of the disease.
A "butterfly" rash can also occur in other conditions such as rosacea and seborrheic dermatitis.