Hyaluronic acid, What Is It?
Hyaluronic acid, also known by the names Hyaluronan or hyaluronate, is a substance that can be found in the human body. Originally thought to be a type of carbohydrate polymer, it has since been re-classified as nonsulfated glycosaminoglycan. Its main function is lubrication; it is one of the important substances in the body that lubricates and cushions various parts of the body, including joints. People who suffer from 
connective tissue disorders may find overly abundant amounts of Hyaluronic acid gathered in the affected areas – joints, eyes, heart valves, etc. It may also have an effect on the skin and joints that deteriorate as we grow older.
Depending on the type of use of the acid, its dose and method of distribution changes.
What Medical Problems Is It Used For?
Hyaluronic acid is used to prolong life, and to treat some of the issues that it seems to be connected to. Examples of these issues are osteoarthritis (hyaluronic acid injections are the newest and most promising treatments), TMJ, glaucoma, ligament healing, cartilage damage, and fractures. It is currently being studied in all of these areas to determine its usefulness in treating these conditions, but it also is in use at the same time.
Medical Studies That Back Up Its Claims
Some of the earliest studies with the acid involved rabbits. Successful eye transplants were done with the aid of hyaluronic acid, which was promising for its use and future with treating humans. Since those earliest days, there have been a multitude of studies and they have been promising or proved successful as a surgical or medical aid.
The United States Food and Drug Administration approved the acid for medical use (eye surgery-related) in 1989.
The use of the acid to treat osteoarthritis is still in practice, but it is a last resort option before surgery. 
There are doubts as to its effectiveness, and studies and trials to ultimately determine its value as a treatment continue.
With crosslinking, the acid becomes a hydrogel, and researchers have found that this is effective for both regenerative medicine and tissue regrowing.
Known as Restylane, the acid has been approved by the Food and Drug Administration to be injected as a wrinkle and other soft tissue filler.
It is still being tested and developed for a variety of uses, and has recently been approved (as Hylan GF-20) as a treatment for various osteoarthritis pain. (link to study here)
Active Ingredients, What Do They Do?
Hyaluronic acid is the sole ingredient in the treatment. It is often the active ingredient in many compounds or other forms of treatments. It can be found in anti-aging creams and treatments.
Side Effects
Hyaluronic acid is generally considered safe for most people to take. However, there is not enough data to determine if it is safe to take orally. When it has been injected, sometimes there is the occurrence of redness, pain or swelling in the area. Post-eye surgery, there have been reports of increased pressure in the eye.
In some rare cases, there have been allergic reactions reported.
Is It Safe?
First and foremost, women who are pregnant or breast feeding should not take hyaluronic acid. There has been some data that suggests that it may in fact be safe when simply injected during pregnancy, but there has been no final determination on its safety in any form during pregnancy or breast feeding. In cases of breast feeding, it is unknown if the acid will get into the breast milk or what effect that would have on the child.
Because abundance of hyaluronic acid can be found at the site of many connective tissue disorders and the areas affected by it, there is still a question of whether or not it is a contributing factor or makes the conditions worse. However, there has been some documentation that, if there is a lack of the acid, it may also contribute to tissue problems. The acid has also been noted to be linked to cases of premature aging disorders.
There is also the issue of hyaluronic acid’s role in the growth of cancer. Researches have noted a correlation between high levels of the acid with certain cancers. The disease may arise when there are levels of the acid outside of the optimal range. Studies have shown that the acid, in higher levels, can aid tumor progression or malignancy. It has been suggested that eradicating the acid may slow or halt tumor aggressiveness and as such would be a new method of cancer treatment or prevention.
Further research shows that in cases of colon cancer, the acid promotes adhesion to laminin. This means that it may also promote or facilitate metastasis of the cancer in the area.
Despite the risks, there are proven benefits to the drug, and it appears that the majority of people and doctors who use it feel the risk is worth it.
