Infiltration is the invasion of body tissues into abnormal cells or the presence of body cells that should not normally be present, as well as the spread of certain diseased tissues to the surrounding area. The presence of abnormal substances or excessive accumulation of pre-existing substances within cells or in the interstitium is also known as infiltration, and some degeneration or deposition is also known as infiltration. Most of the infiltrations are pathologic and have varying effects on the body. In inflammation, various inflammatory cells infiltrate the inflamed tissue, which is the body’s defensive response to resist inflammation and is called inflammatory infiltration. In tumor patients, on the other hand, tumor cells can infiltrate the surrounding normal tissues, called tumor cell infiltration, which is often characteristic of malignant tumors. Of course, any infiltration is harmful to the organism, and the size of the damage depends on the nature and amount of infiltrating material, and the influence of the affected organs.