neurofibromas are tumors composed of soft , growths that are fleshy of nervous tissue . It is possible for them to affect any nerve in the body , but they are most often associated with peripheral nerves - those outside the brain and spinal cord . In particular, they usually involve the nervous tissue connective of the skin . They feel like small pieces of rubbery under the skin . They usually make their appearance during childhood - especially during adolescence . The neurofibromas are generally benign ; However , in 3 percent to 5 percent of the cases , they become malignant . Relationship with neurofibromatosis