Symmetrical black lumps inside the nails of both big toes may be caused by chronic nail trauma that results in subungual bruising, judging by the symptoms. This under nail bruising may form a black lump after a longer period of time. Usually, if it occurs symmetrically, it is likely to be formed slowly by wearing shoes and squeezing. It is recommended to wear loose shoes and observe for a period of time. If the bruising under the nail is caused by wearing shoes, it will generally be relieved gradually after changing to loose shoes, and the normal nails will gradually push the black lump to the outside, and it will gradually subside. If the nail still exists after a period of time after changing to loose shoes, then you need to go to the hospital for an examination, preferably a dermoscopy.