If a person has swelling in the unilateral foot, related causes need to be ruled out for better treatment. At least a few conditions need to be considered: swelling of the unilateral foot with inflammation, especially cellulitis, which can cause swelling of the unilateral foot with redness, swelling, heat, and pain, and requires treatment with topical or oral medications. If a person develops gouty nodules, the skin in the corresponding area can also feel swollen, and there are obvious clues from the medical history or narrative. Mosquito bites or certain traumatic injuries can also present with unilateral foot swelling. Mosquito bites often show redness, while traumatic injuries often have a clear history of trauma, and the patient can clearly look for the cause of the trauma. If the above is ruled out, there is a possibility of poor blood return to the unilateral extremity, commonly due to thrombosis of the unilateral extremity. This thrombosis obstructs venous blood return, thus causing the swelling of the unilateral foot, and the corresponding vascular ultrasound is needed for differential diagnosis. In addition, there may be neuromuscular problems.