A granuloma is a proliferative swelling formed by macrophages and their evolved cells together after the organism has been exposed to some external stimulus.
There are three general causes of granuloma formation:
1. Bacterial infection: e.g. Mycobacterium tuberculosis.
2. Lesions of the immune system: e.g. pulmonary tuberculosis, leprosy, syphilis, etc.
3. Other causes: e.g. trauma, foreign bodies, etc.
Granuloma formation is essentially a delayed metamorphosis, mainly by macrophages, multinucleated giant cells and epithelioid cells, as well as some inflammatory cells, such as: neutrophils, lymphocytes, etc., after stimulation of these cells will infiltrate the skin so that the skin surface to form a nodular lesion, very soft to the touch, and over-exertion will bleed. If this kind of swelling appears on the surface of the skin, you should consult a doctor immediately.