You can buy medical-grade silicone sheets for scar treatment that are taped over moderately-raised scars to flatten them over time (however, they won't work on keloid scars.) They may also help flatten uneven areas from second-degree burns. There are many medical studies that show this method improves the appearance of new scars, though the mechanism is unknown.

It doesn't seem to work as well on old scars. It has been quite successful with new surgical scars. See for example "Effectiveness of Silicone Sheets in the Prevention of Hypertrophic Breast Scars," Annals of Plastic Surgery, 37(4), 345-348, 1996 Oct; and "Effect of Four Treatment Variants on the Functional and Cosmetic state of Mature Scars," Journal of Wound Care, 9(7), 319-324, 2000 Jul (abstracts available on Medline).

You need to keep the scar covered with this material for at least 10 hours per day for about eight weeks to see results. The longer you use the material, the flatter the scar can become, and some people continue for six months or more. There are a few brands of these silicone sheets available at pharmacy counters or in the first-aid section.

Silicone Sheets for Scars 

The sheets are expensive, about $20 to $45 for a 1.5" x 4" piece, but it doesn't wear out. (Rejuveness brand also has different sized face masks available to hold sheets against the face at night.) Some of the brands also sell a special tape to hold the pad in place because regular first-aid tape doesn't stick to it very well. Curad sells less-expensive small, disposable pads called "Curad Scar Therapy" which work on the same principle (see www.curadusa.com). Band-Aid brand also has a similar product.

Some medical studies have also shown that simply keeping a new raised scar completely covered with tight-fitting first-aid tape or athletic tape for at least 10 hours per day for eight weeks works nearly as well as these products. See for example "Prevention of Hypertrophic Scars by Long-Term Paper Tape Application," Plastic and Reconstructive Surgery, 96(7), 1715-1718, 1995 Dec (abstract available on Medline.) The tape should be applied in the direction that best removes skin tension from the scar (your doctor can explain this). It may be easier on the face to use tape or the products from Curad or Band-Aid than the silicone pads.

Tretinoin

Tretinoin may improve the appearance of shallow depressed scars, uneven areas from second-degree burn scars, and some raised scars. See for example "The Local Treatment of Hypertrophic Scars and Keloids with Topical Retinoic Acid," British Journal of Dermatology, 103(3), 319-323, 1980 Sep (abstract available on Medline). Some Net reports claim that copper peptide can also improve depressed and raised scars, though others report little effect. Some people also report improvement by alternating nightly application of either tretinoin or copper peptide and a cosmetic acid.

Dermatologists and plastic surgeons have many techniques available for treating both raised and depressed scars. Laser resurfacing or dermabrasion are often used. See for example "Resurfacing of Pitted Facial Scars with a Pulsed Er:YAG Laser," Dermatological Surgery, 23(10), 880-883, 1997 Oct (abstract available on Medline). (Resurfacing of burn scars should probably be done by manual dermabrasion or with an erbium YAG laser since precise control of penetration depth is necessary.)

However, as with medium resurfacing for treating photoaging, resurfacing of scars doesn't seem to work well on people with oily skin and large pores. Doctors can also treat scars by surgically removing them and stitching the skin closed or replacing the scar with a skin graft. Small pitted scars can be replaced with a skin graft taken from behind the ear in a relatively inexpensive office procedure. Various materials can also be injected under depressed scars to elevate them.
When you look for a doctor to do this work, try to find a dermatologist or plastic surgeon who does a lot of work on "scar revision," since they can offer you more treatment options.

Prevention

Something should also be said about preventing scars. Acne scars can be avoided with early, aggressive treatment. Treatments are now available that will stop the inflamed lesions that can cause scars. If you are going to have surgery, discuss your concerns about scars with your surgeon in advance, so that he or she will close the incision (not an assistant) and use techniques to minimize scar formation.

If have a job or hobby where you could have injuries from flying debris, hot material or chemicals, you should wear the appropriate protective equipment on your face and body. While safety glasses are good for protecting your eyes, you should protect your whole face with a clear plastic face shield (these are available at most hardware stores). You can save a lot of time and money by preventing scars, rather than having to treat them.