While the facial effects of rosacea and lupus may sometimes be confused, the presence of eye symptoms may point definitely to rosacea, as it almost never occurs in lupus flares.

"The presence of ocular involvement can be very helpful in differentiating active lupus from active rosacea," said Dr. Guy Webster, associate professor of dermatology at Jefferson Medical College.

The two disorders may have a similar appearance. Like rosacea, lupus sufferers often have redness across the central portion of the face, often in a butterfly pattern. Although both rashes can be smooth in texture, especially in early rosacea, the presence of bumps and pimples, which rarely occur in a lupus flare, may help differentiate the two diseases.

Moreover, unlike lupus, as many as 50 percent of rosacea patients may also have ocular signs. Visually, an eye affected by rosacea often appears simply to be watery or bloodshot. Patients may feel a gritty or foreign-body sensation in the eye, or have a dry, burning or stinging sensation.

Inflammation of the eye or eyelid, called blepharitis, is also very common in rosacea, Dr. Webster said.