Skin cancer is a reason for sores that won't heal, according to About.com. When these sores are found on the legs or feet, they can also be caused by poor circulation, diabetes, varicose veins, smoking and high blood pressure, explains Cleveland Clinic.
Other causes are clotting disorders, a build-up of lymph fluid that causes the legs to swell, inflammatory disease such as lupus or vasculitis, and sickle cell anemia, says Cleveland Clinic.
There are three types of skin cancer, according to About.com. They are squamous cell and basal cell skin cancer and melanoma. Squamous and basal cell skin cancers often present as sores that won't heal. Fortunately, both are highly treatable when they are caught early. Basal cell skin cancer, or carcinoma, rarely spreads.
There are three common types of leg and foot ulcers, notes Cleveland Clinic. They are venous stasis ulcers, diabetic ulcers and arterial, or ischemic, ulcers. Venous stasis ulcers are located below the knee but above the ankle and are found on both legs. They drain green or yellow pus if they are infected.
Diabetic ulcers are a complication of diabetes and are often found on the bottom of the patient's feet, says Cleveland Clinic. However, if they are the result of an injury, they can be located anywhere on the foot. They not only affect diabetics but anyone who has lost sensation in his foot. Arterial ulcers are located on the toes or the toenail bed.