Is Radiant Skin Just About Hydration — or Firmness Too?

Summary in Three Lines

• Radiance is the impression skin gives when light comes back from it evenly. It is created by light that bounces straight off the surface (surface reflection) together with light that enters the skin and comes back out (subsurface reflection). Oily shine from sebum is not the same thing.
• Hydration is an ingredient of radiance: in a randomized study, the side treated with a hyaluronic acid skin booster received higher radiance scores from photographs. Even at the same level of hydration, though, skin tone and texture change the way light comes back.
• Expert consensus treats firmness as a foundation of good skin quality. Firmness treatments work in different layers, and for none of them have we found a study that measured radiance itself directly. We suggest dealing first with the one thing that is dulling your radiance most.

What Radiance Is — Skin That Returns Light Evenly

Put simply, radiance is the light that comes back from your skin. That light can be divided into two broad kinds.

• Surface reflection — light that bounces straight off the outer surface of the skin.
• Subsurface reflection — light that travels into the skin, scatters, and comes back out.

In an image-analysis and perception study from Japan, photographs of the faces of 45 people were shown to 30 respondents, who rated their radiance (Matsubara et al., 2012). The radiance people perceived was explained by two things taken together: how much light came back from beneath the surface, and how the light reflected from the surface was distributed. In other words, radiance is a balance between surface shine and inner brightness.

The same researcher also carried out a cross-sectional study comparing 83 Japanese women in their 20s to 40s by age group (Matsubara, 2012). How evenly the surface reflection was spread and how strong the subsurface reflection was both differed with age, but the hydration measurement showed no difference between age groups. Even with similar hydration, then, the way light comes back can differ. Younger skin showed stronger subsurface reflection and more even surface reflection, and the researcher suggested this might connect with the common impression of young skin as glowing from within and older skin as looking shiny. Because the study compared age groups at a single point in time, however, it cannot tell us what caused the differences.

Oily Shine Is Not Radiance

Skin that looks shiny because of sebum is closer to a state in which only the light glinting off the surface stands out. The key to radiance is not how much light comes back but how evenly it comes back. If your skin is shiny because it produces a lot of oil, it may make more sense to look first at the oil and the texture than to add more moisture.

Hydration — Hydrating Skin Boosters Really Are an Ingredient of Radiance

Hydrating skin boosters (injections of non-cross-linked hyaluronic acid, known in Korea as mulgwang or "water-glow" injections) can help radiance. In a randomized split-face study, non-cross-linked hyaluronic acid (HA) was injected into one cheek and saline into the other, three times at monthly intervals (Baspeyras et al., 2013; 55 participants). A trained panel scored standardized photographs without knowing which cheek was which. Three months after the last injection, radiance scores had risen on the HA side and dropped slightly on the saline side, and the difference between the two sides was statistically significant. These were changes in scores given to photographs; the amount of light coming from the skin was not measured directly.

In the same study, dermal thickness on the HA side had increased at three months, and the elasticity measurements shifted in the direction of less stiff skin. The difference in these elasticity values compared with the saline side, however, did not reach a clear level of statistical significance. These were the results of one specific product given three times at monthly intervals, in a study run by the product's manufacturer, and they should be read with that in mind.

An expert consensus that defined the components of good skin quality also lists skin boosters among the treatments that help radiance, by restoring hydration and stimulating the skin (Goldie et al., 2021). So hydrating injections are not simply about looking dewy for a little while. Why the same injection can work differently from person to person is explained separately in our column on why skin boosters sometimes seem not to work.

Hydration is an ingredient no radiance plan can leave out. Not every concern about radiance starts with dryness, though.

Texture and Tone — Why Light Looks Different at the Same Hydration

Imagine two pieces of silk under the same light, one crumpled and one smoothed flat. The fabric is identical, but on the crumpled piece the light scatters in all directions and looks patchy, while on the flat piece it comes back smoothly. Skin texture (pores, fine lines, rough flaky skin) is like the creases in the fabric, and skin tone (melasma, spots, redness) makes the color of the returning light uneven.

In a randomized split-face study, 50 Thai women applied a serum containing vitamins C and E and other ingredients to one side of the face only, for 8 weeks (Rattanawiwatpong et al., 2020). On the treated side, gloss measurements improved at weeks 4 and 8 and the melanin index fell, so the tone looked brighter, yet skin moisture did not differ between the treated and untreated sides. Moisture stayed the same while the gloss measurement went up. This study looked at a single topical serum over 8 weeks, and it was funded by a company.

It is the same picture as in the age-group study above, where hydration was similar but light came back differently. Simply evening out tone and texture can change how radiant the skin looks.

So when melasma, redness or rough texture is the main thing hiding your radiance, we recommend sorting out tone and texture first, with treatments such as laser toning, vascular lasers or peels. In such cases, we think the right order is to find out what is blocking the light before adding more and more hydrating injections.

Firmness — What Expert Consensus Calls a Foundation

An expert consensus reached by 10 aesthetic dermatologists and physicians using a Delphi method describes good skin quality in four categories (Goldie et al., 2021).

• Is the tone even?
• Is the surface (texture) even?
• Is the skin firm?
• Does the skin glow?

Firmness here means the overall elasticity (viscoelasticity) of the skin and the tissues beneath it, and it includes the ability to spring back (elasticity), the ability to hold up (tautness), and even the hydration of the epidermis. Hydration is part of firmness, in other words, so the two do not move separately. Glow, by contrast, is the one category of the four with no subcategories of its own, because radiance is not a single component but an impression created when several factors come together. The same consensus also notes that what we see at the surface can start in, or be affected by, deeper tissues, so topical approaches alone may not be enough.

A follow-up consensus then turned this framework into a treatment sequence (Kerscher et al., 2025; 12 experts). The experts strongly agreed that firmness is the foundation for managing the other three categories. Without the support of firmness, refining radiance may have only a limited effect on the impression the face gives as a whole, so they advise attending to tone, texture and firmness first and refining radiance after that. As treatments for firmness they listed microfocused ultrasound (MFU-V), diluted CaHA and ablative fractional lasers. They also noted that skin that is too taut and hard is not desirable either, which is worth keeping in mind: tightening as much as possible is not the goal. Because there are very few direct comparisons between treatments, however, the consensus itself states that the sequence was set on the basis of expert experience.

Research also links the structure inside the skin with light. In a study that measured the skin of the inner arm optically in 28 people, light scattering in the dermis decreased with age, and the researchers interpreted this as reflecting changes in collagen density and structure (Golmajer Zima et al., 2024). It concerned the inner arm rather than the face, and it did not look at the effects of any treatment.

In Dr. Jeong's judgment, when the skin is firm enough to support its texture, light may come back from it a little more evenly. No study we have found, however, has directly measured how much radiance changes after firmness improves. So firmness is not a treatment that replaces radiance; think of it instead as looking after the skin's elasticity so that radiance can appear even.

Firmness Treatments — Each Works in a Different Layer

Firmness treatments act on different layers of the skin. The overview below is not meant to rank them; it is meant to help match a treatment to the layer that needs support. We should say at the outset that for none of the four have we found a controlled study that measured radiance itself directly.

Diluted CaHA — A Collagen Stimulator Spread Thinly Beneath the Dermis

This is a collagen stimulator made of fine particles of calcium hydroxylapatite (CaHA) suspended in a gel (CMC). It is originally used as a volumizing injection to fill hollows, but when diluted and spread thinly and widely beneath the skin, it can be used to firm the skin itself rather than to add volume.

In a pilot study, diluted CaHA was injected into 20 people with lax skin on the neck and upper chest (décolletage), and tissue samples were taken at 4 and 7 months. Type I and type III collagen, elastic fibers (elastin) and new blood vessels all increased, and these changes matched improvements in skin elasticity measurements and increases in dermal thickness measured by ultrasound (Yutskovskaya and Kogan, 2017). It was a 20-person study without a control group, and the results concern the neck and upper chest, not the face. For the face, a retrospective study reviewed 40 people treated with diluted CaHA to improve the skin of the mid and lower face: aging scores had improved after 4 months, and skin imaging showed changes in collagen pattern and increased vessel density (Rovatti et al., 2020). This study had no control group either.

Diluted CaHA is therefore more accurately seen as a firming treatment that supports radiance by strengthening the dermis than as an injection that adds glow right away, as hydrating injections do.

Ulthera (MFU-V) — Lifting That Tightens Lax Tissue and Smooths Texture

Ulthera is a procedure that tightens tissue by creating tiny thermal coagulation points at each transducer's set depth while viewing the inside of the skin on an ultrasound screen; the depth seen on screen and where heat actually forms can differ. In an observational study, 22 women with sagging along the jawline and under the chin received a single Ulthera treatment, and their skin elasticity and hydration measurements were followed for 24 weeks (Kerscher et al., 2019). At week 4, during the swelling phase, elasticity values dipped temporarily; by weeks 12 and 24 they were significantly higher than before treatment, while skin hydration and barrier function (transepidermal water loss) stayed the same. It was a 22-person study without a control group, and the results concern the lower face and under the chin. That it raised firmness beneath the surface without disturbing the surface is a meaningful point for radiance.

A review also sorted the effects of Ulthera into firmness, texture, tone and glow (Pavicic et al., 2025). Of 703 records screened, 67 studies were included: 52 on firmness, 35 on texture, 4 on tone and 4 on glow (some studies fell into more than one category, so the numbers do not add up to the total). The evidence, in other words, is concentrated on firmness and texture. The 4 studies grouped under glow actually looked at things such as melasma and elasticity, and the review itself states that no study has yet directly measured the effect of Ulthera on glow. Glow is inferred only indirectly, from improvements in elasticity and texture.

The expert consensus mentioned above explains that skin looking brighter after Ulthera is due less to pigment fading than to texture becoming smoother so that light scatters less (Goldie et al., 2021; expert opinion). What to expect from Ulthera is firmness and texture; radiance is a change that may follow on from those.

Re2O — Allogeneic Dermis That Replenishes the Dermis Itself

Re2O is an injectable human acellular dermal matrix (hADM): donated human skin from which all cells have been removed, with the remaining dermal tissue processed into very fine particles. This dermal framework is called the extracellular matrix (ECM), a mesh of collagen, elastic fibers and water-binding components, and the product consists mostly of collagen. The inner-arm study above interpreted the change with age as a change in the density and structure of dermal collagen, and the dermis itself is exactly what Re2O targets. Rather than prompting the skin to make collagen, it replenishes dermal components directly, which sets it apart from collagen stimulators.

In a randomized, double-blind split-face study, 20 adults with rough cheek skin received Re2O on one cheek and non-cross-linked HA alone on the other, and were followed for 20 weeks (Lee et al., 2026). Differences between the two sides were reported in skin density, elasticity, wrinkle depth, pore area, hydration, barrier measures and pigmented area. The differences emerged gradually: from week 8 for hydration and physician assessment, and from week 12 for pores. In the rat experiments in the same paper, fibroblasts were seen moving into the injected material and forming new collagen there, but that part is an animal result. It is a single study of 20 people over 20 weeks, the Re2O injections also contained HA, and an author who advised on the product's development took part. Because the number of sessions is reported differently in the paper and in the trial registration, we have not stated it here.

Because Re2O is a material that fills the dermis, when Dr. Jeong uses it on its own, he places only part of it with a cannula and injects the rest by hand into the dermal layer, spreading it so that very small, closely spaced raised bumps form at the surface.

GOURI — Liquid PCL That Supports the Skin From Beneath the Dermis

GOURI is a particle-free liquid collagen stimulator made of PCL (polycaprolactone), a material long used in medicine, for example in absorbable sutures. Dr. Jeong mainly lays it down broadly just beneath the dermis with a cannula. Because it is a thin liquid, it spreads easily through the looser layer beneath the dermis but does not rise far into the denser upper dermis. He therefore explains it as laying a thin mesh (a scaffold) beneath the dermis to support the skin above. This picture of how it spreads is his explanation, based on the formulation and the properties of the tissue.

Human studies of liquid PCL are still few. In a prospective single-arm study of 30 people, liquid PCL was injected just beneath the dermis (in the superficial subcutaneous layer) three times at monthly intervals and followed for 6 months; elasticity measurements changed in the direction of less stretching when the skin was drawn up by suction (Thongjaroensirikul et al., 2026). Because there was no control group, the authors themselves noted limits to drawing conclusions about efficacy and mechanism. Notably, skin hydration values actually fell in the same study. Without a control group the cause cannot be known, but it shows that a firmness treatment does not take the place of hydration, which is one more reason to look at surface hydration and deeper firmness together.

A retrospective study that reviewed 30 people who received liquid PCL in the midface twice with a cannula also reported improvements in skin texture, elasticity and volume over 6 months (Ponzo et al., 2025). The product name was not stated, and the material was placed in the deep dermis for volume. On whether PCL makes collagen in human tissue, a study took biopsies from 2 people 13 months after a particle-type PCL filler was injected into the dermis and found new collagen formed around the particles (Kim and Van Abel, 2015). Because that was a particle-type product, the result cannot simply be carried over to the liquid form, and we did not find human tissue data for liquid PCL in this review.

There is also a caution. Rare bruising lasting several months has been reported in 7 cases, under the eyes, at cannula entry points and on the arm (Byeon et al., 2026). The authors interpreted it as bruise pigment being trapped in the dense PCL mesh and clearing slowly, and all cases eventually resolved. Rarely, an allergic reaction can also persist for a long time. And if sagging comes from deep fat or the retaining ligaments, GOURI alone has limits, so lifting treatments should be considered as well.

How Do These Connect to Radiance?

Dr. Jeong's view is that when Re2O makes the dermis denser and smooths pores and texture, or when GOURI supports the layer beneath the dermis, light may come back from the skin a little more evenly. Because no study has directly measured radiance for either, this is an interpretation based on theory. Since they target different layers, both may be planned together for someone whose dermal density and overall support are both lacking; because no comparative study of the two used together has been found, this is his judgment based on the layers involved. If the concern clearly sits in one layer, one treatment is enough, and we recommend considering both only when both layers need support. The differences between the two are explained in detail in our column on how GOURI and Re2O differ.

Here are the four side by side.

The question to ask about firmness treatments, then, is not which one ranks highest but which layer of your own skin needs support.

Combining Treatments — What Is Known and What Is Not

With several firmness treatments available, the question "Wouldn't it work more if I combined them?" comes up naturally. The combination with the most human studies so far is Ulthera (MFU-V) with diluted CaHA.

A systematic review that gathered human studies of the two used together found 11 studies out of 4,019 records, most of them before-and-after comparisons (Amiri et al., 2025). Global aesthetic improvement scores and skin elasticity and texture measures improved, biopsies showed increased production of collagen and elastic fibers, and no serious adverse events were reported. All 11 studies, however, were judged to have designs in which the influence of other factors is hard to rule out, and the tissue results came from a single person's sample in each study.

There is also one randomized pilot study that compared the order directly (Doyle et al., 2025; 12 people). One group had Ulthera first and diluted CaHA 6 weeks later; the other group had the reverse order; both were followed for 120 days. Global improvement scores and self-perceived age scores differed by treatment order, while participants' own ratings of the jawline were similar in both groups. In the tissue, the change in the area occupied by elastic fibers also differed by order, but that is a change in elastic fiber area, not a sign that elasticity or radiance improved to the same degree. The study did not explain why a 6-week interval was chosen.

In short, using the two together is a combination with consistently reported improvements in sagging and firmness, and on treatment order there is only a single 12-person study. That combining them makes radiance last longer, or doubles the effect, has not been shown. Dr. Jeong first looks at whether each treatment is needed on its own, and for people whose firmness is already good, he explains that there is no need to add it.

What We Look At in Clinic — Starting With What Hides Radiance Most

"So where should I start?" Sooner or later, it comes down to this question. In a consultation about radiance, we look at four things in turn.

1. Hydration — whether your skin feels tight underneath and whether makeup flakes. If your skin stings, we look at the skin barrier first.
2. Tone — whether melasma, spots or redness are blocking the light.
3. Texture — whether pores, fine lines or rough flaky skin are scattering the light.
4. Firmness — how well the skin springs back when gently pinched and released, and whether there is sagging. Pinching and releasing the skin is also the method the treatment consensus above recommends for assessing firmness (Kerscher et al., 2025).

As the table shows, there is more than one route to radiance. That is why we recommend a plan that first deals with the one thing hiding your radiance most, and then checks together whether firming treatment is needed. If an important event is coming up, hydration comes first; if you are taking the long view, we work on tone and texture and on firmness as well.

As we see it, surface hydration provides radiance for now, while deeper firmness supports that radiance so it looks even. You do not need to have every treatment; the first step is to find the one thing your skin lacks most right now. Simply coming in and saying "My skin has lost its glow" is enough for us to decide together where to start.

Precautions and Limits of the Evidence

This article is general information based on research reviewed up to October 31, 2026, and it does not replace individual medical care. Even with the same treatment, results and how long they last can vary with skin thickness, age, skin condition and previous treatments.

After injection treatments, bruising, swelling, redness and pain can occur, usually settling within a few days. Collagen-stimulator injections can rarely cause palpable nodules, and rare bruising lasting several months has been reported with liquid PCL. After Ulthera there may be temporary swelling, tightness or numbness. Please be sure to tell us before treatment if you are pregnant or breastfeeding, take anticoagulants, have an autoimmune disease, or have had fillers or thread procedures in the past.

The relationships between radiance and hydration, texture and tone rest on perception and cross-sectional studies and small clinical studies, and the view of firmness as a foundation of good skin quality is at the level of expert consensus. Most studies of diluted CaHA, Ulthera and GOURI had no control group or were small, and for Re2O there is a single randomized split-face study (Lee et al., 2026). For none of the four treatments did we find a study that measured radiance directly, nor did we find human tissue data for liquid PCL or a comparative study of Re2O and GOURI used together. The link between firmness and radiance is an interpretation based on the evidence, and we found no evidence that combining treatments makes radiance last longer.

The two expert consensus papers cited (Goldie et al., 2021; Kerscher et al., 2025), the Ulthera review (Pavicic et al., 2025), the systematic review of the combination (Amiri et al., 2025) and the sequencing study (Doyle et al., 2025) were supported by the company that makes Ulthera and a CaHA product, and some authors disclosed advisory, speaking or employment relationships. Authors employed by the manufacturer also took part in the Ulthera elasticity and hydration study (Kerscher et al., 2019). The hydrating injection study (Baspeyras et al., 2013) was carried out by the product's manufacturer, and the serum study (Rattanawiwatpong et al., 2020) was company-funded. In the Re2O study (Lee et al., 2026), one co-author advised on the product's development and the manufacturer supplied the test product. Some authors of the liquid PCL bruising case series (Byeon et al., 2026) are members of the manufacturer's research team, and some authors of the prospective liquid PCL study (Thongjaroensirikul et al., 2026) have received lecture fees from the manufacturer. We have interpreted each study with its design and limitations in mind.

References

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From Consultation Through Treatment

A board-certified dermatologist examines you directly, identifies which layer the cause sits in, sets the device and the parameters, and then carries out the procedure as the same physician. This is not a structure in which a consultant sells the treatment.

The number of sessions, the intervals, the maintenance point and the cost are agreed together before the first session.

Related care: Skin Booster Rejuvenation Treatment in Seoul · Collagen Stimulator Treatment in Seoul