Why can't people with autoimmune diseases take melanin?

Wrong word. Melanin is producted by skin cells in response to sun light and is responsible for darkening the skin. Melatonin is a hormone that has been linked in some studies as a possible cause for autoimmune hepatitis (liver disease). Persons who have already developed one autoimmune disease are at higher risk for developing another type of autoimune problem and this may be the origin of this recommendati.
Melanin and autoimmu. Where did you read or hear this? Melanin is a substance that can be affected by autoimmune disease and ingestion of external melanin supplements will have no benefit, but I have not heard about this contraindication. Did you discuss this with a rheumatologist?