4 Answers

A skin ulcer is a crater-like formation on the skin that is caused by any number of reasons, from an infection to cancer or inflammation, report doctors at the National Institutes of Health. Ulcers are sores that typically do not heal properly or keep returning. Ulcers may or may not cause pain. Many people with skin ulcers experience a burning or itching around the area of the wound as well as discomfort from the swelling that usually accompanies an ulcer. Ulcers also may be accompanied by a red rash, a brown discoloration around the sore and dry, flaky skin.

Read more: http://www.livestrong.com/article/25245-causes-skin-ulcers/#ixzz2PQuWNxg6

My late mother had ulcers on her ankles which were cured by the application of Manuka honey.

Ulcer can be caused by several different diseases, conditions or infections.
Pyoderma gangrenosum is a rare disorder of the immune system that causes large ulcers on the skin, usually on the legs.
Bedsores are skin ulcers that are also called pressure sores.
Buerger's disease is a blood vessel disorder that causes blood clots and inflammation in the blood vessels of the arms and legs.

Oh, a number of reasons. Chemical (battery acid), natural (too much sun), and physical (perhaps it's an allergic reaction or decubidus ulcer). Keep them clean and dry and if they persist, see a doctor for antibiotics or physical closure .....