The immune system protects the body from harmful or foreign substances. One of the ways it does this is by sending special cells to protect organs threatened by these substances. The special cells cause other cells to destroy the threat, but this process causes inflammation. Normally, once the threat is resolved, the cells go away, and the inflammation subsides.
Sarcoidosis is a condition in which these immune system cells cluster together. These cell clusters are called granulomas. The most common areas for granulomas to grow are the lungs, lymph nodes, eyes, and skin, but sarcoidosis can affect any organ or area of the body.