Hyaluronic Acid (HA) is a common ingredient used in moisturizers for the purpose of increasing topical drug application efficacy, anti-aging, and as a solution to dry skin. It has many functions within the human body, and its high-water retention allows it the ability to be used either by itself or in combination with other ingredients with a high level of effectiveness.
Hyaluronic Acid, termed occasionally as “nature’s moisturizer,” is a high-molecular weight carbohydrate that is bound together by sugar molecules (making it a type of molecule called a biopolysaccharide).1 It was first discovered in 1934 inside the eyeball of a cow,2 and is responsible for skin hydration, joint lubrication, filling space within the skin, and creating the framework that cells use to migrate.3 It was first used commercially as an egg-white substitute (in 1942)1, but it was then discovered that skin contains fifty-percent of its total volume within the body and its effects in dermatological functions began to be studied.2,3
HA is predominantly known for its unique capacity to retain water within a state between solid and liquid called viscoelasticity. The higher the molecular weight of Hyaluronic Acid being used (which can be modified through laboratory processes), the more effective it is in water-retention.2 The most unique part of HA is its capacity to attract and retain water molecules that are roughly one-thousand times the weight of its own molecules.4 It is able to do this through its hygroscopic (the ability to attract moisture) and hydrophilic (water-loving) properties, which allow it to form large concentrations of water in certain areas of the skin (such as the dermis and epidermis).4,5
The overall hydration of the skin is entirely dependent on the amount of water bound to Hyaluronic Acid molecules within the dermis, as well as the most vital areas of the epidermis, and the skin’s moisture is maintained out of the continued survival of the stratum granulosum (the waterproof layer of the epidermis that prevents water loss during the shedding of dead skin cells).3
The loss of water in the epidermis, prevented by the presence of HA in the stratum gransoleum barrier, subsequently results in the loss of collagen and elastin (responsible for maintaining skin plumpness and texture); the water that supplies the barrier is sourced from the dermis and is stopped by the other side of the membrane, which is made of lipids (that prevent the further release of water).3
Hyaluronic Acid present in the dermis allows a regulation of water volume, pressure, ion flow, and stabilizes the different structures of the skin using electrostatic properties.3 As aging occurs, while the dermal HA remains, the epidermal Hyaluronic acid is significantly reduced — as demonstrated, in studies, by the large presence of HA in infants versus the elderly.6
The topical application of Hyaluronic Acid inherently allows its, and other ingredients’, absorption into keratin (protein build-ups such as blackheads), epidermal, and dermal layers which allow the stratum granulosum layer to rebuild (which, consequently, results in the production of collagen and elastin) and acne-treating ingredients to be able to target difficult-to-access cells.2 It is able to be absorbed through three key functions of the skin: specific HA receptors that are able to place the absorbed HA into the correct locations, the structure of HA which allows it to penetrate, and its ability to hydrate the surface area of the skin. These functions allow Hyaluronic Acid, and the ingredients with it, to be retained in the epidermis.2
The two conditions that Hyaluronic Acid is most commonly used to treat are visible signs of skin-aging and dryness. As aging is signified by a thinning of the skin and a loss of elasticity from intrinsic (the natural unpreventable process)/extrinsic (photoaging or other sources of skin damage) sources, a loss of moisture contributes to the visible appearance or representation of both disorders.3,7
Whether intrinsically or extrinsically aged, there are elevated levels of degraded collagen synthesis as the damage/aging of the skin increases.3 Hyaluronic Acid is able to directly increase the collagen levels of the skin and treat superficial wrinkles through the augmentation of specific collagen-producing tissues within the skin.7 Its anti-aging effect is accomplished through its multifunctional properties of collagen-restoration, water-binding, the ability to moderate tissue hydration, and to heal wounds within the skin.8
Dry skin tends to occur (along with aging) from the decrease of Hyaluronic Acid within the skin, which results in reduced dermal hydration and its resultant redness.7 A popular ingredient in cosmetics for its (clinically-proven) ability to improve tissue hydration, it is able to accelerate the healing process of dry and damaged areas.6
One of the more-common types of dry skin is called actinic keratoses (AKS) (scaly spots or patches) that are normally induced by sunlight. Hyaluronic Acid has been studied as a treatment method for AKS, and a significant decrease in severity was observable within 60 to 90 days of regular and consistent application.6
Hyaluronic Acid’s topical application also increases the hydration of the stratum corneum which allows a soothing protective film that helps to prevent further damage to the functioning of the skin, and actively reduces the recurrence of inflammation. It has been proven to assist with different forms of dry skin (xerosis, atopic dermatitis, ichthyosis, etc.) with up to 78.5% improvement recorded in the treated areas.7,9
Hyaluronic Acid, as an ingredient found naturally within the body, has no major adverse reactions that have been recorded.2,7 There are no issues of biocompatibility (where the body rejects a new ingredient) as it is found within almost every species — which limits the likelihood of allergic or systemic reactions upon application.