Large flat bumps and itchy legs may be related to acute urticaria, flat warts, lichen planus and other causes. 1. Acute urticaria: often self-conscious itchy skin, soon itchy parts of the appearance of the size of the red red masses, round, oval or irregular, the skin surface is uneven. 2. flat warts: caused by human papilloma virus infection of the skin on the legs, for small rice grains to soybean size, round or oval flat raised skin papules, some patients will feel slight itching. 3. Flat moss: typical skin lesions appear to be purplish-red flat papules occurring on the limbs, with clear boundaries, hard and dry texture, white reticular stripes, mostly accompanied by itching. There may be other reasons for the large flat pimples on the legs and itchy, it is recommended to go to the hospital in a timely manner, to clarify the cause of the disease, and standardized treatment under the guidance of the doctor.