The cause of sarcoidosis is not known. And, there may be more than one thing that causes it.

Scientists think that sarcoidosis develops when your immune system responds to something in the environment (e.g., bacteria, viruses, dust, chemicals) or perhaps to your own body tissue (autoimmunity).

Normally, your immune system defends your body against things that it sees as foreign and harmful. It does this by sending special cells to the organs that are being affected by these things. These cells release chemicals that produce inflammation around the foreign substance or substances to isolate and destroy them.

In sarcoidosis, this inflammation remains and leads to the development of granulomas or lumps.

Scientists have not yet identified the specific substance or substances that trigger the immune system response in the first place. They also think that sarcoidosis develops only if you have inherited a certain combination of genes.

You can't catch sarcoidosis from someone who has it.

More research is needed to discover what causes sarcoidosis.