A foreign body granuloma is a mass of cells surrounding an object in the body. Normally, when something enters the body, whether by injection, accident, or infection, cells called macrophages attack the object and basically eat it. If the object is too large for the macrophages to destroy or otherwise cannot get rid of, they cluster around the object and form a granuloma.
Visible symptoms of a foreign body granuloma include a painful tumor-like lump, reddened and infected skin, or small red bumps, although they are not limited to forming just at or below the skin level. Granulomas may form within the brain or other parts of the body. Animals are also susceptible to granulomas, which can cause inflammation and, at least for laboratory animals, make it harder for surgery to heal.
Granulomas do not need a large solid object to occur. They can form around anything, even liquid particles like tattoo ink, especially red ink. Injected silicone is also a trigger for foreign body granuloma formation, as are surgical cotton, piercings, and cholesterol crystals found in injured and poorly drained ears. Bacterial infections can be another basis for the formation of granulomas.
Treatment for a foreign body granuloma depends on its location and the reason for its formation. In some cases, corticosteroids are the preferred treatment, but in others, such as cholesterol granulomas in the middle ear, the lump must be removed. Granulomas can also cause atrophy or thinning of the surrounding skin. A foreign body granuloma is not always round and may have an asymmetric shape that projects into the tissue, making surgery difficult and undesirable in some cases.
Whether or not a foreign body granuloma will form around something is unknown, and having one does not mean that a person will form them repeatedly or develop them in response to everything. Granulomas can also occur at any time, meaning they could form long after the object or substance was introduced. "Dermal fillers" such as collagen used in cosmetic procedures tend to produce multiple granulomas at the sites where the filler was injected at the same time, and these may resolve on their own. If they don't, medications like corticosteroids are the next step in treatment.