Most of the reasons for the sudden thickening of thighs are caused by excessive accumulation of fat in the legs, which may be caused by the excessive intake of high-calorie and high-fat food like pork and doughnuts in a short period of time, and the infrequent aerobic exercise like skipping rope and jogging, which prevent the fat of the whole body from being decomposed in time, and in the long run, the fat accumulates in the thighs, leading to the thickening of thighs. In addition, if there is no problem of overeating and good eating habits, the sudden thickening of the thighs may also be caused by some diseases, such as thrombophlebitis of the lower limbs can easily cause edema of the lower limbs, making the thighs thick. If the thighs are thick because of the disease factor, you must go to a professional hospital for leg examination in time to confirm the cause of the disease, and then take relevant drugs for targeted treatment.