Hyaluronic acid is a natural, body-own substance that is primarily found in the joints and connective tissue. In combination with water, hyaluronic acid forms a viscous gel. This allows hyaluronic acid to optimally serve as a water reservoir and lubricant in the body.
Functions of Hyaluronic Acid in the Body
Hyaluronic acid is an important component of skin, mucous membranes, joint fluid, and the vitreous body of the eye. Here you can learn everything about the functions that hyaluronic acid fulfills in the human body.
Water Storage
One gram of hyaluronic acid can bind up to six liters of water. This immense water storage capacity makes hyaluronic acid a universal helper throughout the body. It is found almost everywhere in the human organism, but about 50% is located in the skin and in the intercellular spaces between skin cells. There, it provides stability and elasticity by binding water. Interactions of hyaluronic acid with other substances allow for the formation of a stable network from the various cell layers of the skin, the extracellular matrix, and the connective tissue. Hyaluronic acid also plays an important role in the vitreous body of the eye. The vitreous body is the large, central area of the eye that is transparent to light. It is filled with a mixture of 2% hyaluronic acid and 98% water. This mixture forms a viscous gel that is interspersed with collagen fibers. Here, hyaluronic acid ensures the elastic yet stable consistency of the vitreous body and its transparency.
Hyaluronic Acid as a Lubricant and Shock Absorber
Water is hardly compressible. Physicists and engineers take advantage of this poor compressibility of liquids in shock absorbers and hydraulic systems. The same is true in the human body. In connective tissue, hyaluronic acid causes water to be bound, thus providing protection against shock and pressure. In the jelly-like core of the intervertebral discs, a hyaluronic acid gel absorbs the pressure forces that occur. Due to its viscous consistency, hyaluronic acid-containing gels also act as lubricants. In joints, the gel adheres to the articular cartilage and forms a slippery layer. A special feature makes hyaluronic acid particularly important in joints: the gel changes with the applied forces. It becomes more fluid the stronger the forces are. This property is called structural viscosity. The knee joint is optimally cushioned under strong pressure forces, such as when standing or jumping, because the joint fluid acts as a shock absorber. During movement, the lubricating function comes to the forefront, reducing joint wear. During rapid shear movements of the joint – for example, in the knee joint while running – the synovial fluid (joint fluid) becomes more fluid, and friction in the joint decreases.
Formation of Proteoglycans
The tasks described so far relate to free hyaluronic acid. Other functions of hyaluronic acid are related to its involvement in the formation of large molecules in the body, known as proteoglycans. These are molecules where polysaccharides (glycans) are bound to a protein framework. An important proteoglycan is aggrecan, which is a component of hyaline cartilage. This type of cartilage is found wherever there are high pressure loads, such as on most joint surfaces. Thus, hyaluronic acid not only protects the joints in the joint fluid but also in the form of proteoglycans in the articular cartilage.
Use of Hyaluronic Acid in Medicine
For medical applications, sodium hyaluronate, the sodium salt of hyaluronic acid, is usually used. It was previously obtained from rooster combs but is now mostly produced biotechnologically. Hyaluronic acid is used in human medicine in various areas.
Hyaluronic Acid for the Joints
In cases of osteoarthritis and wear and tear of the joints, a preparation containing hyaluronic acid can be injected directly into the joint. There, it increases the lubricity and also acts as a shock absorber. Additionally, hyaluronic acid forms a thin layer over the articular cartilage, protecting it from damage caused by inflammatory molecules. Depending on the preparation, between one and five injections may be necessary, usually administered weekly. Hyaluronic acid injections are particularly common for knee osteoarthritis. However, they can also be used for osteoarthritis in the hip joint or for the regeneration of various joints after injuries. However, statutory health insurance does not cover the costs, as the effectiveness has been assessed very differently in studies. Another option is the oral administration of hyaluronic acid in the form of dietary supplements. The hyaluronic acid then reaches the site of action through the bloodstream. While injections achieve higher concentrations of hyaluronic acid in the joint, oral intake is painless, and the joint capsule does not need to be damaged by injections.
Application of Hyaluronic Acid in the Eye
For dry eyes, watery eye drops often only provide short-term relief. This is different when they contain hyaluronic acid. Hyaluronic acid ensures long-lasting moisture for the eye and a stable tear film. Eye ointments also adhere longer to the eye but often initially impair vision after application. Hyaluronic acid eye drops, on the other hand, do not impair vision. Hyaluronic acid is also often found in cleaning solutions for contact lenses. Additionally, hyaluronic acid can be found in some nasal sprays or throat lozenges to protect and moisturize the mucous membranes. Hyaluronic acid is also used by ophthalmologists and in specialized eye clinics. During surgical procedures on the eye, such as cataract surgery, hyaluronic acid solutions can fill the vitreous body or stabilize the anterior chamber of the eye.
Other Medical Applications of Hyaluronic Acid
New areas are continually being discovered where hyaluronic acid has medical benefits. In certain forms of incontinence, hyaluronic acid is successfully injected around the urethra. This treatment is primarily used for stress incontinence. During physical exertion, such as lifting weights, as well as during sneezing or coughing, involuntary leakage of urine occurs in stress incontinence. The so-called Implacement therapy leads to a cushioning of the tissue around the urethra by injecting four depots of hyaluronic acid gel with a syringe. Another application area for hyaluronic acid is vesicorenal reflux in children. Here, there is a backflow of urine from the bladder into the renal pelvis. Stabilized hyaluronic acid can be injected into the ureter via an endoscope. This resolves the reflux in 50 to 90% of patients.
Use of Hyaluronic Acid in Aesthetic Medicine
In cosmetic surgery, hyaluronic acid has long been used for filling wrinkles and for plumping or shaping lips and other facial or body areas.
Filling of Wrinkles
In aesthetic medicine, hyaluronic acid is most commonly used to fill wrinkles. Typical application areas include frown lines (on the forehead), the glabellar line (between the eyebrows), or the nasolabial fold (extending from the wing of the nose towards the corner of the mouth). However, other areas of application are also possible, including the neck, décolletage, or back of the hands. The injected hyaluronic acid not only plumps up the wrinkles and skin tissue but also activates skin regeneration by stimulating fibroblasts (cells in connective tissue).
Tightening, Shaping, and Volume Building
As the elasticity and firmness of the skin decrease over time due to natural skin aging or influences such as UV rays, certain areas of the face often appear sunken. A gel made from stabilized hyaluronic acid can make the facial contours tighter again and positively change the profile. Filling with hyaluronic acid can also be useful in other areas where volume needs to be added. Too thin or too sagging lips can be reshaped. Even a correction of the nose is possible with hyaluronic acid without surgery if only minor asymmetries are present. In a similar way, breast augmentation can be performed. Compared to surgery and the use of implants, such a significant increase is not possible. However, for balancing differently sized breasts or for adding a bit more volume and firmness, a hyaluronic acid gel that is injected between the breast gland and breast muscle is suitable.
Treatment of Dents and Scars
Scars or dents can often be burdensome, especially when they are found on the face. By injecting hyaluronic acid gels, dents can be plumped up and scars can be concealed. This method is suitable, for example, for acne scars or scars resulting from surgeries or injuries. Unevenness in the skin surface after liposuction can also be balanced with hyaluronic acid.
Use of Hyaluronic Acid in Cosmetics
In cosmetic advertising, hyaluronic acid is ubiquitous. Numerous eye gels, day, night, or anti-wrinkle creams contain hyaluronic acid and are intended to combat wrinkles and make the skin firmer. Here you can learn about the benefits of topical application of hyaluronic acid and whether hyaluronic acid can actually penetrate into the deeper layers of the skin.
Effect of Hyaluronic Acid on the Skin
Hyaluronic acid is a natural component of human skin. It binds water and ensures, through its gel-forming properties, that skin and connective tissue remain plump and cushioned. This natural function has primarily protective properties. The side effect is also: Well-hydrated skin with hyaluronic acid is smoother and has fewer wrinkles. With increasing age, the body produces less hyaluronic acid. This makes the skin drier, more sensitive, or prone to wrinkles. When hyaluronic acid is supplied externally, it acts in the skin just like the body's own substance. Those who do not want to have their wrinkles filled can resort to a serum or cream containing hyaluronic acid. The advantage is that the creams are relatively inexpensive and do not require painful injections. Many people already regularly use a skin cream, so applying it does not represent an additional effort.
Chemical Structure of Hyaluronic Acid
Hyaluronic acid belongs to the polysaccharides in its chemical structure. These are long-chain carbohydrate molecules where many individual sugars (monosaccharides) are connected together. Well-known polysaccharides include starch (amylose and amylopectin), cellulose, or glycogen, which serves to store glucose in the body. If a polysaccharide consists of only a single, repeating monosaccharide building block, it is called a homoglycan. In contrast, a heteroglycan is composed of at least two different monosaccharides. Hyaluronic acid belongs to the heteroglycans and can be classified into the group of glycosaminoglycans. It consists of two monosaccharides: glucuronic acid and N-acetylglucosamine. These two simple sugars combine to form a disaccharide. 250 to 50,000 of these disaccharides form a hyaluronic acid molecule. This long chain winds into a helix.
