Usually, the skin heals itself over time. BUT, there are some situations where skin sores just keep getting progressively worst, such as bed sores, skin cancers, and diabetic wounds. Bed sores must be diligently dealt with by consistent ointments and air exposure with pressure relief. 
Skin cancers are another story.* These sores are very serious and need professional health care to not allow them to get bigger or out of control. Skin cancers should never be allowed to get to the late stage, you should have long ago been to your Doctor. But that does not necessarily mean you can just sit back and not take an active role in supporting your professional medical care protocols by assisting the healing process from both inside the body as well as outside.
This is a rather remarkable personal story. One that is not recommended you copy if you have access to medical care. Get professional care first. Not getting early professional care could yet prove to be a large mistake.
STORY: I read about a skin health formula being used to heal wounds including skin cancer sores. I remembered reading about a similar application where cartilage was used internally for joint health and cancer prevention. The original research used cartilage chips placed in skin wounds to speed healing. It turned out that the people taking oral cartilage also exhibited less cancers and their arthritis and joint pain improved. The researchers changed their study direction and the cartilage skin wound healing connection was quietly overshadowed, at least in the vitamin industry. But this application is used in medical settings by Doctors aware of this research. This next reference is very complete in wound healing details plus quite graphic pictures are depicted. But, there is no mention of using ground cartilage, although consuming vitamin C is mentioned. ref
How might cartilage help wound healing?
There are a number of ways. Cartilage contains Glycosaminoglycans (GAGs) or mucopolysaccharides such as Glucosamine and chondroitin. Glucosamine helps build collagen and more cartilage and it also stimulates hyaluronic acid production, another GAG, which speeds up the healing process. ref
OF INTEREST: This is a good place to reveal another vital concept seldom mentioned in nutrition. The thickness of the skin naturally gets thinner as one ages. BUT, there are processes that speed it up and nutrients that slow this thinning down. Have you noticed how thin an older smoker's skin gets much earlier than a non smoker. Smoking quickly uses up vitamin C since vitamin C is needed to detoxify smoke elements. Vitamin C is necessary to build collagen, a vital component of skin elasticity and thickness. Plus, the skin is also made up of elastin fibers that cross the collagen. A simple test that reveals the age of the skin is to pinch and stretch a small part of the skin and see how quickly it bounces or springs back into its original position. As one ages, this recovery process slows down and the pinch marks remain visible longer. The criss-crossing elastin and collagen fibers are breaking down. There are enzymes responsible for this action. Anti-oxidants slow this process down, especially those contained in grape seed extract, or OPC's. Dr Perricome likes Carnosine to prevent protein folding and the resulting formation of glycation spots (AGES). AGES stands for Advanced Glycation End Spots. ref ref
THE SKIN FORMULA
The skin formula was made up of bovine cartilage powder, ascorbic acid (vitamin C) powder, and a drop of DMSO to carry it into the skin. Not having DMSO, I just used the two powders and mixed them up, about a dime sized pinch of each with a couple drops of water in my cupped palm. This makes a clear slimy consistency film. You just have to re-wet it on the skin every few minutes since it rapidly dries out. Leave it on for about 15-20 minutes, them shower off. This application was applied to a skin sore that was not healing on it's own and had lasted for many months. It was on my chest about 4 inches below the neck line, a high sun area from wearing open neck button up shirts. The sore would scab over and the scab would catch on my shirt and crack open and bleed. When it changed shapes and colors, the thought entered that it was a pre-cancerous lesion. After mixing this brew and applying it every night for many months, the sore begin to slowly heal and eventually went away completely about six months later. Today it is hardly noticeable.
WHY IT IS UNWISE NOT TO GET PROFESSIONAL CARE
This occurred at a time when I didn't have health care insurance and couldn't afford it being self employed and a young man with a growing family. I did have a policy for a short period, but it was too expensive even then and I had to let it lapse. Skin cancers, similar to most cancers, can metastasize and spread to other tissues and organs. If my sore was cancerous, it could have spread and again be waiting to erupt or be already building in other body areas. UPdate: Now, 30 years later, irregular activity is appearing at this spot that needs attention due to my age, 74. One other small cancer spot was cut out, but the original spot is still normal.
This is where you have some weapons to use to keep the immune cells on full alert to find and destroy DNA damaged cells before they can multiply and develop into tumors. When cancers get large enough to be noticed, Doctors measure the blood and find that natural immune Killer Cells are less in numbers and are too low in energy to fight off the growing tumor cells.
HOW TO KEEP KILLER CELLS ACTIVE and PLENTIFUL
Researchers long ago discovered that people who consume more vegetables and fruits tend to have fewer of certain cancers, plus a reduction was also seen in those who exercise regularly. ref Something in vegetables and fruits must perk up the immune system killer cell activity. Scientists have now pinpointed some of these phytochemicals, such as SGS from broccoli and other cruciferous vegetables, and beta glucans from mushrooms. ref And in fruits there are many flavonoid compounds with similar effects. Many of these give fruits their bright colors. From whole brown rice comes inositol hexaphosphate. ref Plus, you might recall from an earlier article that excess unmetabolized folic acid, a synthetic B vitamin, reduced killer cell activity by 22% (about the same as sugar) in one study. article
Thus, you have plenty of natural killer cell enhancers to use in your battle to get and stay healthy. Monitor your skin health at the very least monthly. And remember, anti-oxidants have a balance point. Not too much, not too little, but just the right amount wins the health game.
OF INTEREST: Vitamin A slows down skin aging by balancing CCN1 destructive activity on type 1 collagen production. ref
SUNSHINE VITAMIN D and SKIN CANCER
The following information is part of the puzzle that escapes many professionals. While skin cancer, squamous cell carcinoma, is caused by ultraviolet sunlight, it is also indirectly prevented by sunlight too. Vitamin D produced by sunlight, goes into the body and gets converted into an active hormone form when blood calcium levels get low. This hormone form goes into skin cells and prevents damaged skin cells from turning cancerous. How this happens; hormone vitamin D triggers genes to prevent HA breakdown products from acting on damaged cells. ref