Erythema multiforme is a skin condition that can develop as a hypersensitivity reaction to drugs or an infection, although there are many other causes of this disorder, with new ones being found every year. Although the specific mechanism of the disease isn't known, it appears that sensitivity to bacterial, viral, and chemical irritants leads to an acute immune response involving the small blood vessels of the skin and the eruption of flat, circular, red patches, resembling targets with dark centers. The patches usually develop suddenly, appearing on arms, legs, palms, hands or feet and, sometimes, on the face or lips. They may or may not itch and may be accompanied by fatigue, fever, and joint pain. Some people also develop abnormalities of vision, including dry or bloodshot eyes, eye pain, burning or itching, or mouth sores.
I discussed your question about scarring with Robin Ashinoff, M.D., chief of Dermatologic, Mohs and Laser Surgery at Hackensack University Medical Center in Hackensack, Hackensack, NJ. She told me that the scars from erythema multiforme can leave a noticeable change in the surface of the skin, and the affected area can be either raised or depressed. Dr. Ashinoff said that these may improve by the application of silicone dressings and topical wound lacquers, which are sold over-the-counter at drug stores in the section where bandages are sold. She said you could also massage hard or raised scars to soften or flatten them. Use any type of lubricant, and massage for five to 10 minutes several times a day. Topical vitamin E may help, too, but Dr. Ashinoff tells me that about 30 percent of patients develop an allergic reaction to it.
Erythema multiform can also cause darkening of some areas of skin (hyperpigmentation). You can treat this with topical bleaching creams containing hydroquinone (non-prescription products are available over the counter; you'll need a prescription for a higher concentration). Other creams that may help are kojic acid (stop using it if causes irritation), unpasteurized soy milk (apply twice a day for 12 weeks) and topical vitamin C.
Andrew Weil, M.D.
Here's more information on erythema multiforme.