Hyaluronic Acid Serum Guide: Evidence-Based Benefits, How to Use It, and Choosing the Best Formula for Your Skin

Key Highlights
Introduction
What Hyaluronic Acid Is and How It Works in Skin
Molecular Weight, Forms, and Why They Matter
Concentration: Does Percent Matter?
Vehicles and Texture: How Formulation Influences Efficacy
How to Layer Hyaluronic Acid Serum in a Skincare Routine
Combining Hyaluronic Acid with Other Active Ingredients
Clinical Benefits and Evidence: What the Studies Show
Choosing the Right Hyaluronic Acid Serum for Your Skin Type
Common Myths and Misconceptions
Side Effects, Sensitivity, and When to See a Professional
Storage, Shelf Life, and Stability
DIY Hyaluronic Acid: Risks and Limitations
Real-World Examples: How HA Serums Fit into Different Routines
Product Selection Checklist
When Hyaluronic Acid Won't Solve the Problem
Emerging Directions and Advanced Delivery Systems
Cost Considerations and How to Get the Best Value
Measuring Effectiveness: How to Know a Serum Is Working
Practical Tips for Daily Use
FAQ

Key Highlights

Hyaluronic acid (HA) serums boost skin hydration by attracting and holding water molecules; different molecular weights determine whether HA hydrates surface layers or penetrates deeper.
Proper layering, concentration awareness, and ingredient pairing (retinoids, vitamin C, exfoliants) maximize benefits while minimizing irritation; formulations and delivery systems matter more than marketing claims.
Safety profile is strong for most people, but formulation quality, preservatives, and additives determine tolerability; preserved, pH-stable serums with clear ingredient lists deliver the most predictable results.

Introduction

Hyaluronic acid serums have become a cornerstone of daily skincare routines, lauded for their immediate hydrating effect and touted as a universal booster for skin health. The term appears on product labels across price points, from drugstore gels to medical-grade ampoules. The popularity rests on a simple premise: HA attracts water and holds it within the skin, smoothing fine lines and restoring a supple appearance. The reality is more nuanced. Molecular size, vehicle, concentration, co-ingredients, and application technique influence outcomes—and not all hyaluronic acid serums are created equal.

This article explains how hyaluronic acid works, what distinguishes one serum from another, how to select a product for your skin type and goals, and how to incorporate HA into a broader skincare regimen safely and effectively. The guidance combines biochemistry, evidence from clinical studies, and practical recommendations that dermatologists and estheticians use. Expect clear, actionable advice and realistic expectations for short- and long-term benefits.

What Hyaluronic Acid Is and How It Works in Skin

Hyaluronic acid is a glycosaminoglycan—a long chain carbohydrate—naturally present in human tissue, especially the skin, eyes, and joints. Its chemical structure enables strong water-binding: a single HA molecule can hold up to 1,000 times its weight in water. Within skin, HA contributes to the extracellular matrix, supporting hydration, elasticity, and volume.

Topically applied HA does not rebuild the extracellular matrix on its own, but it changes the skin’s water content. When hyaluronic acid sits on the skin surface, it draws moisture from the air and underlying layers. That process plumps the stratum corneum and minimizes the appearance of fine lines. Over time, improved hydration can support barrier function and enhance comfort for dry or sensitized skin.

The extent of benefit depends on molecular weight and formulation. High-molecular-weight HA tends to form a film on the skin surface, which prevents transepidermal water loss (TEWL) and provides visible smoothing. Low-molecular-weight HA can penetrate to the epidermis to provide more intrinsic hydration and signal certain cellular processes. Manufacturers often combine molecular weights to deliver both immediate surface plumping and deeper hydration.

Molecular Weight, Forms, and Why They Matter

Not all hyaluronic acid molecules behave the same. Manufacturers and researchers categorize HA by molecular weight:

High molecular weight (HMW-HA): Usually >1,000 kDa. Creates a hydrating film on the surface, reduces water loss, calms inflammation, and gives immediate smoothing.
Intermediate molecular weight: Around 500–1,000 kDa. Offers a balance of surface and limited epidermal interaction.
Low molecular weight (LMW-HA): Below ≈500 kDa. Capable of penetrating the epidermis and influencing cellular hydration and some signaling pathways.
Oligo-HA or very low molecular weight: Small fragments sometimes associated with different biological effects, including inflammatory signaling in certain experimental contexts.

What manufacturers often sell under the label “hyaluronic acid” is sodium hyaluronate, the salt form that is more stable and easier to formulate. Sodium hyaluronate penetrates more readily than native HA because of its lower molecular weight. Hyaluronic acid derivatives—cross-linked HA or esters—appear in specialized products to extend hydration delivery or produce filler-like effects in topical form. Those derivatives alter behavior: cross-linked forms resist degradation and provide longer-lasting surface hydration.

Select a serum that lists multiple HA molecular weights for a fuller hydration profile. If a formula promotes only “hyaluronic acid” without specifying type or molecular weight, expect mostly surface hydration.

Concentration: Does Percent Matter?

Ingredient concentration affects performance for many actives, but hyaluronic acid is less straightforward. Laboratory and clinical studies rarely hinge on a single optimal percentage because the ingredient functions primarily by osmosis and film formation. Common concentrations in serums range from 0.1% to 2%; thicker gels and professional ampoules may go higher.

Higher concentrations increase viscosity and surface plumping but can feel sticky if the vehicle is inappropriate. Low concentrations can still be effective if the formula uses multiple molecular weights and a compatible vehicle that allows HA to hydrate rather than sit as an inert film. For dehydrated or mature skin seeking immediate smoothing, a mid-range concentration coupled with HMW-HA for surface film and LMW-HA for epidermal hydration works well.

Pay attention to the full ingredient list rather than percent alone. Humectants like glycerin and propanediol, occlusives like squalane, and emollients shape the HA’s performance. A 1% HA serum with glycerin and a lightweight emollient typically outperforms a 2% product with poor formulation.

Vehicles and Texture: How Formulation Influences Efficacy

Hyaluronic acid is water-loving, so serums often rely on aqueous vehicles. The texture, absorption speed, and finishing skin feel derive from the combination of humectants, thickeners, solvents, and emollients.

Lightweight water-based serums: Rapid absorption, non-greasy finish. Ideal under moisturizers and makeup.
Gel formulations: Provide a cooling sensation and immediate surface plumping. Works well for oily or combination skin.
Creams or emulsions containing HA: Combine humectant action with lipids for barrier repair. Better for dry skin because occlusives reduce TEWL.
Ampoules and treatment boosters: Concentrated serums often packaged for short-term intensive hydration.

Ingredients to watch:

Glycerin and propanediol: Synergize with HA as humectants.
Alcohol denat: Speeds drying but can irritate; avoid high levels in sensitive skin formulas.
Fragrance: Adds irritation risk; fragrance-free options are preferable for sensitive or acne-prone skin.
Preservatives: Necessary for aqueous serums. Phenoxyethanol and ethylhexylglycerin are common; look for reputable systems to prevent contamination.

Formulators balance immediate sensory appeal with functional performance. A sticky HA serum might indicate an overly high concentration or insufficient co-ingredients to reduce tackiness. A watery serum that disappears instantly may lack enough humectants to sustain hydration.

How to Layer Hyaluronic Acid Serum in a Skincare Routine

Timing and layering determine whether HA enhances or undermines skin hydration. The core principle: apply HA on damp skin and finish with an occlusive. Damp skin gives HA water to bind; an occlusive seals that moisture and prevents TEWL.

A practical morning routine:

Cleanse with your usual cleanser.
Pat face gently; leave skin slightly damp.
Apply a few drops of HA serum and spread evenly.
Follow with antioxidant serum (e.g., vitamin C) if used.
Use moisturizer to lock in hydration.
Apply broad-spectrum sunscreen.

Evening routine:

Double-cleanse if wearing sunscreen or makeup.
Apply toners or chemical exfoliants if part of your regimen, then wait for them to absorb.
Put HA serum on slightly damp skin.
Layer targeted actives – thinner products first, retinoids and thicker moisturizers later.
Finish with a nourishing cream or oil.

Avoid letting HA dry completely on skin before applying moisturizer; as it dries, it can pull water from deeper layers if there’s insufficient ambient humidity, which may worsen dehydration. In low-humidity climates, apply HA serum and then a moisturizer immediately.

Combining Hyaluronic Acid with Other Active Ingredients

Hyaluronic acid pairs well with a broad range of actives because it focuses on hydration rather than altering skin cell turnover. Some notable combinations and considerations follow.

Retinoids: Retinoids increase cell turnover and can cause transient dryness and irritation. HA serums reduce dryness and promote barrier function when used alongside retinoids. Apply HA before or after retinoid based on texture—if HA serum is lightweight, use it before to hydrate; if retinoid is in a gel, place HA on top to reduce irritation.

Vitamin C: Vitamin C ascorbic acid is typically acidic and may destabilize some formulations. Use HA serum either after vitamin C serums or layer vitamin C first, allow it to absorb, then apply HA. Combining delivers hydration without interfering with vitamin C’s antioxidant benefits.

Niacinamide: Niacinamide complements HA by strengthening the skin barrier and reducing TEWL. There’s no chemical incompatibility; the two can be used together to improve tone and moisture retention.

Alpha and beta hydroxy acids (AHA/BHA): Chemical exfoliants can increase penetration and transient sensitivity. Apply AHAs/BHAs first, rinse or wait for absorption, then apply HA to soothe and rehydrate.

Peptides: Peptides benefit from a hydrated environment; HA supports peptide delivery by improving epidermal hydration and appearance. Use both for anti-aging routines.

Sunscreen and makeup: HA plays well under sunscreen and makeup, but very watery HA may affect sunscreen spread. Apply HA, wait a moment, then moisturize and sunscreen.

Avoid layering too many actives in a single session if skin is sensitive. Use HA as an ally to cushion and maintain hydration when experimenting with stronger treatments.

Clinical Benefits and Evidence: What the Studies Show

Clinical research substantiates several core benefits of topical hyaluronic acid:

Immediate hydration: Multiple randomized trials show HA increases stratum corneum hydration within hours. Participants often report improved skin smoothness and reduced scaling.
Reduction in fine lines: Short-term plumping from water retention reduces the visibility of fine lines; longer-term studies suggest sustained use improves skin elasticity and appearance, especially when formulations include multiple molecular weights.
Barrier support: HA supports barrier recovery after irritant exposure and may reduce TEWL when combined with occlusives.
Wound healing and anti-inflammatory effects: HA plays a role in tissue repair. Topical formulations (often higher molecular weight) can modulate inflammation and support healing in clinical settings. These effects are more pronounced in controlled medical formulations than cosmetic serums.
Compatibility with other actives: Clinical trials show HA reduces dryness and irritation from topical retinoids, improving tolerability and adherence.

Limitations appear in inconsistent reporting on concentration and molecular weight across studies. Long-term structural changes in the dermal matrix from topical HA alone are modest compared with injectable HA or procedures that stimulate collagen. Expect topical HA to improve hydration and appearance rather than act as a substitute for in-office volumizing treatments.

Choosing the Right Hyaluronic Acid Serum for Your Skin Type

Skin goals, type, and lifestyle should guide product selection. Use these practical guidelines.

Dry, dehydrated skin:

Seek hydrating serums with multiple HA molecular weights and added humectants (glycerin, panthenol).
Prefer formulas with light emollients or that pair with a richer moisturizer.
Avoid high-alcohol or heavily fragranced serums that strip moisture.

Oily or acne-prone skin:

Choose gel or lightweight water-based serums with non-comedogenic humectants.
Avoid heavy oils in the serum itself; layer a lightweight oil only if needed.
Look for serums labeled non-comedogenic or oil-free.

Sensitive skin:

Pick fragrance-free, alcohol-free formulations with minimal additives.
Low preservative allergenicity helps; single-ingredient HA boosters exist but still require preservatives in water-based products.
Patch-test new products before full-face application.

Aging skin:

Opt for serums with combined molecular weights and supportive ingredients—peptides, ceramides, or antioxidants.
Consider products that pair HA with retinoid-friendly delivery systems to minimize dryness.

Climate considerations:

High humidity: HA works well; lighter textures are fine.
Low humidity: Use HA with occlusive moisturizers to prevent net water loss.

Price vs. performance: Expensive packaging or concentrated marketing does not guarantee superior performance. Evaluate ingredient lists, molecular weight information, and product transparency. Proven formulations from reputable brands often outperform unknown or unpreserved DIY alternatives.

Common Myths and Misconceptions

Myth: Topical HA can permanently restore lost collagen or replace injectables. Fact: Topical HA improves hydration and temporary plumping but does not replace the volumizing and structural effects of injectable cross-linked HA fillers. It does not rebuild dermal collagen to the degree seen with lasers, RF, or fillers.

Myth: Higher percent HA always means a better product. Fact: Percent alone is a poor indicator. The formula’s molecular weight mix, vehicle, and co-ingredients define performance and sensory properties.

Myth: Hyaluronic acid causes acne and clogs pores. Fact: HA is a humectant and generally non-comedogenic. Comedogenic reactions usually stem from other ingredients—heavy oils, silicones, or occlusive emollients—in the product rather than HA itself.

Myth: All HA serums are interchangeable. Fact: Formulations differ widely. Molecular weight, additional humectants, preservatives, and the presence of active ingredients produce distinct outcomes.

Side Effects, Sensitivity, and When to See a Professional

Hyaluronic acid has a favorable safety profile for topical use. Adverse reactions are uncommon but can include:

Irritation or stinging: Often from alcohols, fragrances, or preservatives rather than HA itself.
Contact dermatitis: Rare, usually attributable to additives.
Paradoxical dryness: If HA serum is applied to very dry skin in low-humidity settings without a subsequent occlusive, it may pull water from deeper layers as it dries.

Seek professional advice if you experience persistent redness, itching, blistering, or signs of infection. For chronic skin conditions—eczema, rosacea, or compromised barrier—consult a dermatologist before adding new actives.

Pregnancy and breastfeeding: Topical HA is considered safe during pregnancy and lactation because it is non-systemic. If in doubt, confirm with a clinician.

Procedural considerations: If planning in-office treatments (microneedling, lasers), inform the practitioner about your HA products. Some treatments may require pausing certain topical actives. HA itself is typically acceptable but might affect post-procedure care.

Storage, Shelf Life, and Stability

Most HA serums are water-based and require preservatives. Proper storage preserves efficacy and prevents microbial growth.

Shelf life: Unopened serums typically last 1–3 years depending on preservatives. Once opened, expect 6–12 months of effective use for most products; manufacturers increasingly list exact PAO (period after opening) symbols.
Temperature: Store in a cool, dry place away from direct sunlight. Heat speeds degradation of actives and can compromise pumps and preservatives.
Packaging: Airless pumps and single-dose ampoules reduce contamination risk and preserve product integrity. Transparent bottles can degrade faster if exposed to light.
DIY formulations: Homemade HA serums without effective preservatives pose a high contamination risk. Avoid storing water-based DIY serums for extended periods.

If a serum changes smell, color, or texture, discard it.

DIY Hyaluronic Acid: Risks and Limitations

Hyaluronic acid powder is available to consumers for home preparation. While DIY serums might seem economical, risks outweigh benefits for most users.

Preservative necessity: Water-based formulations require proper preservatives to prevent bacterial and fungal growth. DIY preservative selection and dosing can be complex and dangerous if mishandled.
Sterility: Mixing without sterile tools and containers invites contamination.
Efficacy: Homemade serums often lack viscosity control and may not achieve desirable molecular weight distribution or stability.
Cost comparison: High-quality commercial serums use validated preservative systems and stable formulations; the small savings on DIY rarely justify the risks.

If you choose to DIY, use sterile technique, stable preservatives suitable for aqueous formulations, and store products refrigerated for short-term use only. Dermatologists generally recommend commercially produced serums for safety and predictable performance.

Real-World Examples: How HA Serums Fit into Different Routines

Example 1: Student with combination skin and acne-prone areas Morning routine: gentle gel cleanser, lightweight water-based HA serum, niacinamide serum, oil-free moisturizer, mineral sunscreen. Evening routine: oil-based cleanser to remove makeup, gentle foaming cleanser, BHA spot treatment as needed, HA gel to hydrate, lightweight moisturizer. Outcome: HA reduces skin tightness from acne treatments and improves makeup application without adding oil.

Example 2: Office worker with dehydrated mature skin Morning: hydrating cream cleanser, leave-on vitamin C, dual-weight hyaluronic acid serum (HMW + LMW), peptide serum, richer moisturizer with ceramides, SPF. Evening: gentle cleanser, retinoid (every other night), HA serum immediately after retinoid when tolerated, nutrient-rich night cream. Outcome: HA cushions retinoid-induced dryness, and combined actives support improved elasticity and reduced fine lines over months.

Example 3: Athlete in dry climate Routine emphasizes occlusion: apply HA serum immediately post-shower while skin is damp, pair with thick emollient or ointment at night, use humidifier during sleep. Outcome: HA plus occlusion preserves hydration despite low ambient humidity and frequent showers.

These examples show HA’s flexibility when matched to the rest of the regimen. The right complementary products amplify HA’s hydrating effect.

Product Selection Checklist

When choosing a hyaluronic acid serum, evaluate these factors:

Ingredient transparency: Does the product list sodium hyaluronate, molecular weights, or just “hyaluronic acid”?
Molecular weight diversity: A formula that lists multiple molecular weights offers broader hydration.
Humectant partners: Look for glycerin, propanediol, or panthenol to support long-lasting hydration.
Occlusive compatibility: If you have dry skin, ensure the serum layers well under thicker creams or oils.
Avoid irritants: Fragrance-free and alcohol-free options reduce the risk of sensitivity.
Packaging: Airless pumps or ampoules reduce contamination risk and extend shelf life.
Value: Compare performance and ingredient list rather than price tag alone.
Clinical claims: Evaluate whether the brand provides evidence or clinical testing to support claims.

A single high-quality HA serum can serve multiple roles—pre-moisturizer hydrator, post-retinoid soother, and everyday plumping serum.

When Hyaluronic Acid Won't Solve the Problem

Hyaluronic acid excels at improving hydration and the look of superficial fine lines but has limits:

Deep wrinkles and volume loss: Structural dermal changes require collagen stimulation (retinoids, lasers, RF) or injectable fillers to restore volume.
Persistent pigmentation: HA does not correct melanin overproduction. Antioxidants, retinoids, and specific lightening agents are required.
Severe barrier dysfunction: Advanced eczema or chronic dermatitis often needs prescribed topical steroids, non-steroidal anti-inflammatories, or barrier repair therapies beyond daily HA use.

Use HA as part of a comprehensive plan that targets the underlying cause of skin concerns.

Emerging Directions and Advanced Delivery Systems

Researchers and formulators are exploring ways to extend and refine HA’s benefits.

Cross-linked topical HA: Designed to resist enzymatic degradation and maintain surface hydration longer.
Microneedling with HA: Studies test whether HA applied post-microneedling enhances hydration and recovery. Clinical use varies depending on practitioner protocol.
Nano-encapsulation and liposomal delivery: Aims to protect low-molecular-weight HA and optimize penetration.
Combination therapeutics: HA paired with growth factors, peptides, or topical fillers in clinical formulations targets both hydration and tissue remodeling.

These innovations require validation through controlled trials; some hold promise for longer-lasting topical effects but are not standard for daily over-the-counter use yet.

Cost Considerations and How to Get the Best Value

The hyaluronic acid market spans a wide price range. Cost reflects research, formulation complexity, packaging, and brand positioning. To get the best value:

Prioritize ingredient clarity: A mid-priced product with transparent molecular weight listings and supporting humectants often outperforms expensive products with opaque ingredient claims.
Look for clinical data: Brands that publish study results or dermatologist endorsements may demonstrate efficacy.
Focus on formulation synergy: A well-balanced formula that pairs HA with supportive humectants and barrier lipids yields better results than HA alone.
Avoid unnecessary extras: Fragrances, colorants, and exotic but unproven extracts add cost with minimal benefit.

A thoughtful purchase balances price with the features that matter for your skin.

Measuring Effectiveness: How to Know a Serum Is Working

Track short-term and long-term markers.

Short-term (days to weeks):

Immediate sensation: Skin feels less tight and appears smoother after application.
Visual changes: Finer lines look less pronounced; makeup applies more evenly.
Tactile changes: Skin surface feels softer and more elastic.

Long-term (months):

Reduced flakiness and improved barrier function.
Sustained improvement in skin texture and resilience.
Better tolerance to drying actives like retinoids.

Document progress with photographs under consistent lighting and a simple journal noting concurrent routine changes. If no improvement appears after consistent use (6–8 weeks) despite proper layering and occlusion, reassess the formulation and consider professional advice.

Practical Tips for Daily Use

Apply HA to damp skin, not bone-dry.
Pair with an occlusive or moisturizer to lock in gains.
Use morning and/or evening depending on your routine; consistent use yields the best results.
If sensitivity develops, simplify your routine: stop potential irritants and reintroduce HA alone to test tolerance.
Keep products sealed and stored away from heat and light.
For travel, choose single-dose ampoules or ensure refrigeration if advised by the manufacturer.

Small changes in application and product selection produce meaningful differences in efficacy.

FAQ

Q: How quickly will I see results from a hyaluronic acid serum? A: Surface hydration and reduced appearance of fine lines can appear within hours to days. Noticeable improvements in skin texture and barrier function often require consistent use over 4–12 weeks.

Q: Can hyaluronic acid cause breakouts? A: HA itself is generally non-comedogenic. Breakouts usually stem from other ingredients in the product—heavy oils, silicones, or occlusive emollients. Choose oil-free or non-comedogenic formulas for acne-prone skin.

Q: Should I use hyaluronic acid with retinol? A: Yes. HA reduces retinol-induced dryness and irritation. Apply HA on slightly damp skin and then follow with moisturizer. Adjust layering based on product textures.

Q: Is sodium hyaluronate the same as hyaluronic acid? A: Sodium hyaluronate is the salt form of hyaluronic acid. It is more stable and typically used in topical formulations because it penetrates slightly better and is easier to combine with other ingredients.

Q: Can I make my own hyaluronic acid serum at home? A: DIY serums carry contamination risks if preservatives and sterile technique are not used. Homemade aqueous serums can grow bacteria and fungi; commercially produced serums with validated preservative systems are safer and more reliable.

Q: Does hyaluronic acid work for oily skin? A: Yes. Lightweight HA gels hydrate without adding oil. Hydration can actually help regulate sebum production and reduce compensatory oiliness.

Q: How long should I continue using hyaluronic acid serum? A: Ongoing use maintains hydration benefits. Results are reversible—stopping HA will gradually return skin to its prior hydration state. Use continuously as part of your routine.

Q: Is hyaluronic acid safe during pregnancy? A: Topical HA is considered safe in pregnancy and lactation because it is not systemically absorbed. Consult your healthcare provider if you have specific concerns.

Q: Will HA help with deep wrinkles and sagging? A: Topical HA improves hydration and the look of fine lines but does not restore lost facial volume or deep wrinkles to the extent that injectable fillers, collagen-stimulating treatments, or surgical procedures can.

Q: What should I avoid combining with HA serums? A: Avoid mixing in other products in the palm that are not compatible. HA pairs well with most actives, but watch for direct application with acidic toners or products that may neutralize or destabilize sensitive formulations. Apply stronger actives (acidic vitamin C, chemical exfoliants) first, then HA to rehydrate.

Q: How do I store my hyaluronic acid serum? A: Store in a cool, dry place away from sunlight. Use airless or opaque packaging when possible. Discard if color, smell, or texture changes.

Q: Are there any side effects? A: Side effects are rare and typically result from additives like fragrance, alcohol, or preservatives. Discontinue if you experience persistent irritation or allergic reaction and consult a clinician.

Q: Can HA be used on the body or scalp? A: Yes. HA can hydrate the body and scalp. Lightweight sprays or body serums deliver hydration to knees, elbows, and scalp when formulated appropriately.

Q: What is the best concentration to look for? A: No single percentage guarantees superior results. Look for products with a thoughtful blend of molecular weights, supportive humectants, and a stable, well-formulated vehicle rather than fixating on concentration alone.

Q: Are expensive brands better? A: Price does not guarantee efficacy. Evaluate ingredient transparency, molecular weight diversity, preservatives, and formulation synergy. A mid-priced well-formulated product often delivers more consistent results than a high-cost item with poor clarity.

Q: How can I tell if my HA serum is working with other actives? A: Reduced tightness, improved tolerance to irritants, and visible skin texture improvement indicate HA is enhancing your routine. If irritation persists, simplify the regimen and reintroduce products slowly to identify interactions.

Hyaluronic acid serums offer dependable hydration, immediate cosmetic benefit, and a favorable safety profile. Their true value depends on formulation science, correct application, and thoughtful integration with other skincare actives. Select products with transparent ingredient lists, employ smart layering (damp skin plus occlusive), and maintain realistic expectations: HA enhances skin hydration and appearance but is not a cure-all. When used consistently and intelligently, HA serums belong in the toolkit of nearly any effective skincare routine.