Only the esterified forms of fumaric acid are used therapeutically, such as fumaric acid monoethylester or fumaric acid di-methylester. Healthy people do not need to supplement with fumaric acid. Those using this substance (either orally or topically) should work with a dermatologist, since determining the optimal intake should be done on an individual basis. Even under these circumstances, supplementing should be started with small amounts (60–100 mg per day) and increased gradually over several weeks until an effect is noted.