Hyaluronic acid is a natural, endogenous substance that occurs primarily in the joints and connective tissue. In combination with water, hyaluronic acid forms a viscous gel. As a result, hyaluronic acid is ideal for storing water and as a lubricant in the body.
Functions of hyaluronic acid in the body
Hyaluronic acid is an important component of the skin, mucous membranes, synovial fluid and the vitreous humor of the eye. Find out everything about the functions that hyaluronic acid fulfills in the human body.
Storage of water
One gram of hyaluronic acid can bind up to six liters of water. This immense water storage capacity makes hylauronic acid a universal helper in the entire body. It occurs almost everywhere in the human organism, but around 50% can be found in the skin and in the spaces between the skin cells. There it ensures stability and elasticity by binding water. Interactions between hyaluronic acid and other substances enable a stable network to form from the different cell layers of the skin, the extracellular matrix and the connective tissue. Hyaluronic acid also fulfills an important function in the vitreous humor of the eye. The vitreous is the large, central area of the eyes that allows light to pass through. It is filled with a mixture of 2% hyaluronic acid and 98% water. This mixture forms a viscous gel with collagen fibers running through it. The hyaluronic acid ensures the elastic but stable consistency of the vitreous body and its transparency.
Hyaluronic acid as a lubricant and shock absorber
Water can hardly be compressed. Physicists and technicians take advantage of this poor compressibility of fluids in shock absorbers and hydraulic systems. It is similar in the human body. In the connective tissue, the hyaluronic acid causes water to be bound and at the same time provides protection against impact and pressure. A hyaluronic acid gel also absorbs the pressure forces that occur in the gelatinous core of the intervertebral discs. Due to their viscous consistency, gels containing hyaluronic acid also function as lubricants. In joints, the gel adheres to the articular cartilage and forms a lubricious layer. There is one special feature that makes hyaluronic acid particularly important in joints: the gel changes with the forces acting on it. The stronger the forces, the more fluid it becomes. This property is called structural viscosity. The knee joint is optimally padded for strong compressive forces that act while standing or jumping, because the synovial fluid acts as a shock absorber. When moving, the lubrication function comes to the fore, which reduces joint wear. With rapid shear movements of the joint – for example in the knee joint when running – the synovia (joint fluid) liquefies and the friction in the joint decreases.
Formation of proteoglycans
The tasks described so far relate to freely available hyaluronic acid. Other functions of hyaluronic acid are related to the fact that it is involved in the formation of large molecules in the body, the so-called proteoglycans. These are molecules in which polysaccharides (glycans) are bound to a protein structure. An important proteoglycan is aggrecan (or aggrekan), which is part of hyaline cartilage. This type of cartilage can be found wherever there is great pressure, such as on most joint surfaces. Hyaluronic acid not only protects the joints in the joint fluid, but also in the form of proteoglycans in the joint cartilage.
Use of hyaluronic acid in medicine
Sodium hyaluronate, the sodium salt of hyaluronic acid, is usually used medicinally. It used to be extracted from cockscombs, but is now mostly produced using biotechnology. Hyaluronic acid is used in various areas of human medicine.
Hyaluronic acid for the joints
In the case of osteoarthritis and signs of wear and tear of the joints, a preparation containing hyaluronic acid can be injected directly into the joint. There it increases the sliding ability and also acts as a shock absorber at the same time. In addition, the hyaluronic acid forms a thin layer over the joint cartilage, protecting it from damage caused by inflammatory molecules. Depending on the preparation, between one and five injections may be necessary, which are usually given weekly. Hyaluronic acid injections are used particularly frequently for knee osteoarthritis. However, it can also be used for arthrosis in the hip joint or for the regeneration of various joints after injuries. The statutory health insurances do not cover the costs, however, as the effectiveness has been assessed very differently in studies. Another option is oral administration of hyaluronic acid in the form of dietary supplements. The hyaluronic acid then reaches the site of action via the bloodstream. Injecting higher concentrations of hyaluronic acid in the joint is achieved, but oral intake is painless and the joint capsule does not have to be damaged by injections.
Use of hyaluronic acid on the eye
For dry eyes, water-based eye drops often only help briefly. Different if they contain hyaluronic acid. The hyaluronic acid ensures long-lasting wetting of the eye and a stable tear film. Eye ointments also adhere longer to the eye, but often lead to impaired vision after application. Hyaluronic acid eye drops, however, do not affect eyesight. Hyaluronic acid is also often contained in cleaning solutions for contact lenses. In addition, hyaluronic acid is also found in some nasal sprays or throat tablets to protect and moisturize the mucous membranes. Hyaluronic acid is also used by ophthalmologists and specialized eye clinics. During surgical interventions on the eye, for example in the case of cataracts, hylauronic acid solutions can fill the vitreous humor or stabilize the anterior chamber of the eye.
Other medical fields of application for hyaluronic acid
New areas are constantly being discovered in which hyaluronic acid has a medicinal benefit. In certain forms of incontinence, hyaluronic acid is successfully injected around the urethra. This treatment is mainly used for stress incontinence. During physical exertion such as lifting loads, but also when sneezing or coughing, stress incontinence leads to an involuntary leakage of urine. The so-called implacement therapy leads to a padding of the tissue around the urethra by inserting four depots of hyaluronic acid gel there with a syringe. Another area of application 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 using an endoscope. This clears reflux in 50 to 90% of patients.
Use of hyaluronic acid in aesthetic medicine
In cosmetic surgery, hyaluronic acid has long been used to inject wrinkles and to plump or model lips and other parts of the face or body.
Injection of wrinkles
In aesthetic medicine, hyaluronic acid is most commonly used to spray on wrinkles. Typical areas of application are the worry lines (on the forehead), the frown lines (between the eyebrows) or the nasolabial fold (goes from the nostril towards the corner of the mouth). But other areas of application are also possible, including on the neck, décolleté or the back of the hand. The injected hyaluronic acid not only cushions the wrinkles and skin tissue, but also activates the regeneration of the skin by stimulating the fibroblasts (cells in the connective tissue).
Tightening, shaping and building volume
If the elasticity and firmness of the skin decrease over time due to natural 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 firmer again and positively change the profile. Injection with hyaluronic acid can also be useful in other areas where volume needs to be replenished. Lips that are too narrow or too slack can be remodeled. Even a correction of the nose is possible with hyaluronic acid without surgery if there are only minor asymmetries. Breast augmentation can also be performed in a similar way. Compared to an operation and the use of implants, such an immense enlargement is not possible. However, a hyaluronic acid gel that is injected between the mammary gland and pectoral muscle is suitable to compensate for differently sized breasts or to build up a little more volume and firmness.
Treatment of dents and scars
Scars or dents can often be distressing, especially if they are on the face. By injecting hyaluronic acid gels, dents can be plumped up and scars concealed. The method is suitable, for example, for acne scars or scars caused by operations or injuries. Unevenness in the surface of the skin after liposuction can also be leveled out with hyaluronic acid.
Use of hyaluronic acid in cosmetics
Hyaluronic acid is omnipresent in cosmetics advertising. Numerous eye gels, day, night or anti-wrinkle creams contain hyaluronic acid and are supposed to fight wrinkles and make the skin firmer. Find out here what benefits the external use of hyaluronic acid has and whether hyaluronic acid can even penetrate the deeper layers of the skin.
Effects of hyaluronic acid on the skin
Hyaluronic acid is a natural component of human skin. It binds water and, thanks to its gel-forming properties, ensures that skin and connective tissue remain plump and padded. This natural function primarily has protective properties. The side effect is also: Skin that is well supplied with hyaluronic acid is smoother and has fewer wrinkles. With increasing age, the body produces less and less hyaluronic acid. The skin becomes drier, more sensitive or wrinkles. If hyaluronic acid is supplied externally, it works in the skin just like the body’s own substance. If you don’t want to be injected under the wrinkles, you can use a serum or cream with hyaluronic acid. The advantage here is that the creams are relatively cheap and no painful punctures are necessary. Many people use a skin cream regularly anyway, so applying it doesn’t involve any extra effort.
Chemical structure of hyaluronic acid
In terms of its chemical structure, hyaluronic acid is one of the polysaccharides. These are long-chain carbohydrate molecules in which many individual sugars (monosaccharides) are linked to one another. Well-known polysaccharides are starch (amylose and amylopectin), cellulose or glycogen, which is used in the body to store glucose. If a polysaccharide consists of only one single, repeating monosaccharide component, it is called a homoglycan. In contrast, a heteroglycan is made up of at least two different monosaccharides. Hyaluronic acid belongs to the heteroglycans and can be classified in 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.