Hyaluronic Acid
The most popular hydrating ingredient in skincare. Hyaluronic acid (HA) is a glycosaminoglycan naturally produced by the body that can hold up to 1,000x its weight in water. In skincare, different molecular weights serve different functions: high molecular weight HA sits on the skin surface forming a moisture barrier, while low molecular weight HA penetrates deeper layers for plumping hydration.
Hyaluronic acid is the most popular hydrating ingredient in skincare, and understanding molecular weight is key to using it effectively. Your body naturally contains roughly 15 grams of HA, with about 50% in the skin. Natural skin HA turns over rapidly — approximately half is replaced every 24 hours — which is why consistent application matters.
The molecular weight determines where HA works in the skin. High molecular weight HA (>1000 kDa) is too large to penetrate the stratum corneum and forms a hydrating film on the surface, reducing water loss. Medium weight HA (100-1000 kDa) penetrates into the upper epidermis. Low molecular weight HA (<50 kDa) can reach the dermis, where it stimulates fibroblast activity and collagen production — but it can also trigger mild inflammation in some people.
The 'desert climate' problem is real but often overstated. In very low humidity (<30%), HA can draw moisture from deeper skin layers to the surface where it evaporates, potentially worsening dryness. The solution is simple: always apply HA to damp skin and seal immediately with an occlusive moisturizer. This ensures HA draws water inward rather than outward.
Concentration & Usage
Concentrations: 0.1-2%. Higher is not always better — concentrations above 2% can feel sticky and may actually pull moisture FROM skin in dry climates. Multi-molecular weight formulations are preferred. Apply to damp skin and seal with moisturizer.
Application
Topical (serum, cream, mask). Apply to damp skin and layer occlusive on top. Injectable HA fillers are a separate medical category.
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Mechanism of Action
Hyaluronic acid is a glycosaminoglycan (GAG) composed of repeating D-glucuronic acid and N-acetyl-D-glucosamine disaccharides. Its hydroxyl and carboxyl groups create strong hydrogen bonding with water—each molecule binds up to 1000x its weight in water. High molecular weight HA (>1000 kDa) forms a viscoelastic film on the stratum corneum, reducing transepidermal water loss (TEWL). Medium weight (100-1000 kDa) penetrates the upper epidermis. Low molecular weight HA (<100 kDa) reaches the dermis and binds CD44 and RHAMM receptors on fibroblasts, triggering ERK and PI3K signaling that stimulates fibroblast proliferation, hyaluronan synthase (HAS2) expression, and collagen I/III synthesis. Sodium hyaluronate—the salt form—has improved stability and penetration. Multi-weight formulations provide surface hydration and deeper dermal stimulation.
Ingredient Interactions
Both are water-soluble and layer beautifully. HA draws moisture into the skin while niacinamide strengthens the barrier to keep it there. Safe for all skin types including sensitive.
HA draws water into the skin; ceramides seal the barrier so the moisture stays. Apply HA to damp skin, then ceramide moisturizer on top. Universally beneficial.
Both draw moisture into the skin but through different mechanisms. Glycerin is a smaller molecule and provides consistent hydration; HA holds up to 1000x its weight in water at the surface.
Hyaluronic acid helps maintain hydration while retinol increases cell turnover. Apply HA serum first, then retinol, then moisturizer.
No conflicts. Vitamin C provides antioxidant protection while HA maintains hydration. Apply vitamin C serum first (lower pH), then HA.
See our full Ingredient Interactions Guide for more combinations and timing strategies.
Regulatory Status
Cosmetic ingredient. Available OTC worldwide. Also used as injectable dermal filler (medical device, e.g. Juvederm, Restylane).
Risks & Safety
Common
Stickiness at high concentrations. In very dry/arid climates, HA can draw moisture from deeper skin layers to the surface where it evaporates.
Serious
None.
Rare
Mild irritation from very low molecular weight HA penetrating too deeply.
Compare Hyaluronic Acid With
Research Papers
10Published: June 16, 2024
AI Summary
The results showed beneficial effects of both test products, with notable enhancements in dermis density, skin texture, and a reduction in the severity of wrinkles. In contrast, the administration of either of the products did not yield any significant impacts on skin elasticity or hydration.
Published: January 17, 2025
AI Summary
Aging reduces the production of hyaluronic acid (HA) in the skin, leading to wrinkles and sagging. This systematic review and meta-analysis aimed to compare the effectiveness of HA-based injectable products for reducing wrinkles and enhancing skin elasticity, hydration, and radiation.
Published: April 16, 2015
AI Summary
The original work was described in several articles. The objective of this study was to determine whether hyaluronic acid attenuates skin necrosis, and to further clarify its uses in wound repair in humans, animal models and in vitro studies.
Published: July 20, 2020
AI Summary
All these biomaterials are used as wound-covering, anti-adhesive devices and as scaffolds for tissue engineering, such as epidermis, dermis, micro-vascularized skin, cartilage and bone. In this review, the essential biological functions of HA and the applications of its derivatives for pharmaceutical and tissue regeneration purposes are reviewed.
Published: July 31, 2020
AI Summary
Hyaluronic acid (HA), a non-sulfated glycosaminoglycan (GAG), is a major component of skin extracellular matrix (ECM) and it is involved in the inflammatory response, angiogenesis, and tissue regeneration process.
Published: February 15, 2016
AI Summary
Although widely accepted, the conventional methods such as Franz diffusion cells are unable to provide the accurate localization of actives in the skin layers. It presents a high molecular specificity to distinguish exogenous molecules from skin constituents.
Published: July 14, 2023
AI Summary
It is rapidly degraded by the injection of hyaluronidase, thus creating an ideal injectable material that is low risk and reversible. Its duration of effect may be longer than expected based on bioavailability of the HA product due to collagen synthesis or fibroblast stimulation.
Published: November 30, 2023
AI Summary
To evaluate the impact of oral intake of Hyaluronic Acid (HA) on skin health.
Published: December 31, 2017
AI Summary
Indeed, distinct effects are evident after the first session, but a progressive enhancement of skin texture is detectable for up to 12 months after repeat treatment at 4 to 6 month intervals. Thus, a strong consensus was reached that NSB procedures are minimally invasive, safe, and effective, and designed to improve skin texture and maintain ski...
Published: February 29, 2024
AI Summary
Inflammatory skin diseases represent a significant health concern, affecting approximately 20-25% of the global population. However, addressing these challenges is hindered by their chronic nature, insufficient therapeutic effectiveness, and the propensity for recurrence and adverse side effects.
Frequently Asked Questions
What is Hyaluronic Acid used for?
The most popular hydrating ingredient in skincare. Hyaluronic acid (HA) is a glycosaminoglycan naturally produced by the body that can hold up to 1,000x its weight in water. In skincare, different molecular weights serve different functions: high molecular weight HA sits on the skin surface forming a moisture barrier, while low molecular weight HA penetrates deeper layers for plumping hydration.
What are the side effects of Hyaluronic Acid?
Common: Stickiness at high concentrations. In very dry/arid climates, HA can draw moisture from deeper skin layers to the surface where it evaporates. Serious: None. Rare: Mild irritation from very low molecular weight HA penetrating too deeply.
How is Hyaluronic Acid administered?
Hyaluronic Acid is administered via topical (serum, cream, mask). apply to damp skin and layer occlusive on top. injectable ha fillers are a separate medical category..
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