- What is HA? Why this substance has been in us since birth
- Molecular structure + crosslinking — the key that makes filler last
- The water-binding and volumizing mechanism — how much water can one HA molecule hold
- Types of HA: how monophasic and biphasic differ
- G prime — firmness and lifting strength; choosing wrong can leave lumps
- Why the body can break down HA on its own + the filler-dissolving agent
- HA vs permanent fillers/foreign substances — why HA is far safer
- HA filler in Phitsanulok — Depry Clinic
- Frequently Asked Questions
- References and verification
"HA filler" is not a foreign substance. It is Hyaluronic Acid, a substance that already exists in our own bodies — in the skin, in the joints, in the eyes — where it holds water to keep tissues hydrated. Filler is simply this same substance purified and then put through a crosslinking process that links the molecules so they last longer. When choosing a filler, I look mainly at two things: the "texture" (monophasic or biphasic) and the "firmness" (the G prime value), matching them to each area. And the thing that makes HA far safer than permanent filler is this — the body can break it down on its own, and if you're not happy with it, there's an agent that can dissolve it. In this article, Dr. Time will walk you through it all the way down to the molecular level, in a way that even non-doctors can understand.
What is HA? Why this substance has been in us since birth
When patients come to consult me about filler, the question I hear most often — and one I really love — is, "Doctor, you're injecting some unknown substance into my face… is that even safe?" I completely understand this worry, because we should worry like this about anything we put into our bodies.
But when I answer, "Actually, this substance has been in your body since you were born," almost everyone looks startled and asks, "It's in us? Where?" So that's the first thing I'd like to explain here.
HA stands for Hyaluronic Acid, which Thai speakers transliterate as "haiyaluronik aesid," and some shorten to "haiya." It is a natural substance in a group called glycosaminoglycan, which sounds complicated but whose job is very simple — it is the body's "water-holding sponge." And it sits in three important places that everyone shares.
- In the skin — HA is in the dermis, keeping our skin hydrated, plump, and elastic. When we're young, our skin is full of water because there's plenty of HA. As we age, HA decreases, so the skin starts to become dry and saggy.
- In the joints — HA is a main component of joint fluid (synovial fluid), lubricating the joints so they move smoothly without grinding against each other. (This is why some medicines for knee osteoarthritis are also HA.)
- In the eyes — the vitreous fluid in the eyeball also has HA as a key component that helps maintain the shape of the eye.
See? It isn't some "strange thing" at all. It's something our bodies make and use every single second. HA filler is therefore taking a substance the body is already familiar with, purifying it, and putting it back into the spots where it has depleted. This is the first basic reason why HA is highly biocompatible and is not seen by the body as an enemy.
Because HA is the same substance the body already has, it means the chance of the body "rejecting" or being allergic to the HA material itself is very low (what you have to watch out for is the injection technique and product quality, not the HA substance). This is the starting point of why I primarily choose to use HA-group fillers.
Molecular structure + crosslinking — the key that makes filler last
Got questions? Dr. Time offers personalized, honest consultations — no upselling.
Consult Dr. TimeThis is the heart of what I want everyone to understand, because it's the answer to one really good question: "If the HA in our bodies breaks down so quickly, why does filler last a year or more?"
Natural HA — lasts only a few hours
The natural HA molecule is like a single "long chain." Our bodies break it down very quickly with an enzyme called hyaluronidase, so the HA the body makes itself lasts only a few hours to a few days before it's fully gone. If we took raw HA like this and injected it, it would disappear within a day or two — injecting it would be a waste.
Crosslinking — weaving the chains into a net
So scientists came up with a way to make HA last longer, through a process called crosslinking — imagine that HA was originally a single thread that snaps easily. Crosslinking is taking many threads and weaving them together into a 3D net. Once it's a tightly interlocked net, the body's enzymes break it down much more slowly, so the filler lasts for many months to a year.
The substance used as the "linker" in most HA fillers is called BDDE (1,4-Butanediol diglycidyl ether). In a standardized manufacturing process, BDDE reacts until it becomes part of the net structure, and the remainder is washed out until only a very small, safe amount is left. The simple principle I want you to remember is:
- The more crosslinking → the stronger and longer-lasting the filler, and usually the better it supports structure.
- The less crosslinking → the softer, smoother, and more natural the filler, but usually shorter-lasting.
This doesn't mean "firmer is better" or "softer is better." It means "different tools for different jobs," which leads us to two more important matters — the "texture" of the filler and its "firmness." Let me explain each one by one.
The water-binding and volumizing mechanism — how much water can one HA molecule hold
Now let's look at how the "volumizing" we talk about actually happens at the molecular level. I find this part truly beautiful.
HA has a special property: it is "strongly hydrophilic (water-loving)." A single HA molecule can attract and store around 1,000 times its own weight in water. Picture a tiny sponge soaking up water until it swells — when we inject HA filler under the skin, it works two ways at once.
- Adding volume with the gel itself — the crosslinked HA gel has volume of its own, so it pushes the tissue to look plumper the moment it's injected, such as filling in nasolabial folds to make them shallower, or shaping the chin.
- Drawing in water as reinforcement — HA pulls in water from the surrounding tissue and holds it there, making that area look hydrated, with skin that looks fresh and moisturized from within.
This water-binding property is exactly what explains why, in the early period after injection, some people feel a bit "puffy" or look slightly fuller than expected — because the HA is drawing in water and there's still swelling from the procedure itself. So I always tell patients — filler shows a change in volume from the day it's injected, but the result truly settles after the swelling subsides, around 1 to 2 weeks. Don't be alarmed if it looks a little full in the first few days; give the result time to set.
Because HA holds water so well, assessing how much to inject has to "allow" for the water-binding too. Injecting too much in one session can make it look swollen or fuller than natural. So I usually choose to add gradually and reassess, rather than putting in a lot at once, to make the result as natural as possible.
Types of HA: how monophasic and biphasic differ
Now that you understand crosslinking and water-binding, let's look at how HA fillers divide by "texture" into two big families. These are terms patients often hear but rarely have explained to them, so let me explain them vividly.
Monophasic — a single-texture gel, smooth and uniform
Monophasic is filler that is a single uniform gel throughout the syringe, smooth and even like a jelly stirred until it's one consistent mass. Its advantage is that it's easy to spread, flows smoothly, sets evenly, and rarely feels lumpy to the touch. It suits work that requires fine smoothness and a natural look, such as under the eyes, shallow nasolabial folds, and the lips.
Biphasic — a particle gel, giving good lifting support
Biphasic is filler made of small gel particles dispersed in a carrier medium, like little jelly chunks floating in syrup. Its advantage is that it usually provides good lifting support and structural standing, and withstands pressure, making it suitable for structural augmentation that needs to stand up. But because it's particulate, some formulas may feel more palpable to the touch, so the area and technique have to be chosen appropriately.
| Topic | Monophasic (single-texture) | Biphasic (particle) |
|---|---|---|
| Texture | Smooth, uniform gel throughout the syringe | Small gel particles in a carrier medium |
| Spreadability | Easy to spread, flows smoothly, even | Spreadable, but emphasizes holding shape |
| Strength | Smooth, even skin, natural | Good lifting support, holds shape, withstands pressure |
| Suited for | Under-eyes, lips, shallow nasolabial folds, thin skin | Structural augmentation that needs to stand up |
| Simple summary | Focuses on smoothness | Focuses on support |
I want to emphasize — neither type is "better" overall. They are different tools for different jobs. A good clinic or doctor won't use a single filler for every spot on the face, but will choose the texture appropriate for each area. This ties into another important value I'll explain next — the "firmness," or G prime.
G prime — firmness and lifting strength; choosing wrong can leave lumps
If there were one single term I'd want patients to know before deciding to get filler, I'd choose this one — G prime.
G prime is the value that tells you the "firmness and lifting strength" of a filler. Simply put, it tells you how well that filler "holds its stand when pressure is applied." Picture this comparison — high-G-prime filler is like a "firm eraser" that holds its shape when pressed, while low G prime is like "soft jelly" that collapses under force.
High G prime → work that needs to stand up and bear force
Firm, high-G-prime filler supports structure well and doesn't collapse easily, so it suits areas that need a clear "structure" and must bear force, such as the chin, nasal bridge, jawline, and cheekbones. If you use a filler that's too soft for these jobs, it will collapse and not form a shape.
Low/soft G prime → thin-skin work that needs smoothness
Soft, low-G-prime filler is smooth and blends well into thin skin, without forming ridges or lumps, so it suits the under-eyes, lips, and very thin-skinned areas. If you use a filler that's too firm for these jobs, you may feel lumps, see ridges, or get an unnatural look.
| Area | Suitable G prime value | Reason |
|---|---|---|
| Chin | High (firm, good support) | Needs structural standing and to bear force |
| Nasal bridge | High (firm, good support) | Must hold a straight ridge, no drooping |
| Jawline / cheekbones | High to medium | Lifts and gives clear facial structure |
| Nasolabial folds | Medium | Adds volume but still needs to be smooth |
| Lips | Low to medium (soft) | Must be soft, moving naturally |
| Under-eyes | Low (very soft) | Very thin skin, must be smooth without lumps |
Choosing a filler with the "wrong G prime" for the area is a common cause of problems — for example, using something too firm under the eyes so you feel lumps or see bluish ridges (the Tyndall effect), or using something too soft in the chin so it collapses and won't hold a shape. This is why filler is "not something just anyone can inject," and why choosing the right filler type for each area is a medical judgment, not just picking up a needle and injecting. If you want to understand the big picture first, read the easy-to-understand filler guide, and if you're interested specifically in lips, see lip filler.
Why the body can break down HA on its own + the filler-dissolving agent
Now we come to what I consider the "biggest safety advantage" of HA filler, and the main reason I choose to use it.
The body gradually breaks down HA on its own
Because HA is the same substance the body already has, the body already has an enzyme that breaks it down naturally (the hyaluronidase enzyme mentioned earlier). So crosslinked HA filler isn't permanent — it is gradually broken down on its own, slowly, until it eventually disappears completely. The duration depends on the filler type, the injection site, and each person's body. The advantage is that if you don't like the result, you just "wait" and it goes away on its own — it won't stay with you for life.
Hyaluronidase — the agent that can dissolve filler if you don't want to wait
And here is the true hero of safety — hyaluronidase is an agent that a doctor injects to "dissolve HA filler" faster. If the result is unsatisfactory, asymmetric, lumpy, overfilled, or there's some complication, the doctor can use this agent to "reverse" the result.
Think about how reassuring this is — HA filler is one of the few cosmetic procedures that is "reversible." If you have it done and don't like it, it isn't a decision that binds you forever. I consider this excellent structural safety, especially in the hands of a doctor who knows how to use hyaluronidase correctly when needed.
The fact that HA filler is "reversible" doesn't mean it's fine to inject carelessly and fix it later. It means that if anything doesn't go as hoped, we always have a safe way out — unlike permanent substances, which can hardly be fixed once injected.
HA vs permanent fillers/foreign substances — why HA is far safer
I want to close the science part with the most important comparison, because it's the reason I always warn patients to avoid the "permanent fillers" and "foreign substances" that some places still secretly use.
"Permanent filler" here means substances that, once injected, the body cannot break down, such as liquid silicone, paraffin, or various foreign beauty-enhancing substances that some people mistakenly believe are "more worth it because they last longer." In reality, they are a long-term risk that is very hard to fix.
| Topic | HA filler | Permanent filler / foreign substance |
|---|---|---|
| Is it a substance in the body? | Yes, the body already has it | No, it's a foreign substance |
| Can the body break it down on its own? | Yes, gradually broken down naturally | No, it stays permanently |
| Is there an agent to dissolve/correct it? | Yes (hyaluronidase) | Almost none, usually requires surgical removal |
| Long-term risk | Low, reversible | Chronic inflammation, lumps, drooping |
| If you're not satisfied | Wait for it to dissolve, or inject the dissolving agent | Very hard to fix, may stay forever |
You can clearly see why HA is far safer. Permanent foreign substances often cause the body to develop a long-term rejection reaction, forming hard lumps (granuloma), chronic inflammation, or drooping with gravity over many years, and when you want them removed it's very difficult, sometimes requiring surgery — whereas HA is "reversible" and the body can handle it on its own.
So I use only genuine HA filler that has passed FDA verification. Beyond the type of substance, being a verified genuine product is just as important. If you want to understand the big picture of choosing filler and the related services, read on at the filler guide, or see all of the clinic's services.
HA filler in Phitsanulok — Depry Clinic
If you live in Phitsanulok or a nearby province and would like to consult about HA filler in a way that you understand before deciding, Depry Clinic would be glad to take care of you. Here, Dr. Time assesses and looks after every case personally. Many of my patients travel from Phichit · Sukhothai · Uttaradit · Kamphaeng Phet · Phetchabun because they want someone who genuinely explains things so they understand, and who chooses the filler that suits each person's face.
Because I understand all the science behind this — from crosslinking, monophasic/biphasic texture, all the way to the G prime value — I can choose the filler type suited to each area of your face: firm material to support structure for the chin and nose, soft smooth material for the under-eyes and lips. None of this is to show off; it's so that you can be confident the person injecting you truly understands what they're doing.
If you'd like to consult about filler in a way where you understand before doing it, with no course pushing, message Dr. Time to talk. The consultation is free, at no charge.
Frequently Asked Questions
What is HA filler? Is it a foreign substance injected into the body?
It's not a foreign substance at all. HA, or Hyaluronic Acid, is a substance that already exists naturally in our own bodies, found abundantly in the skin, joint fluid, and the fluid of the eyes, where it holds water to keep tissues hydrated and elastic. HA filler is this same substance purified and made to last longer, then put back into the spots where volume has been lost. So the body is familiar with it and gradually breaks it down on its own naturally.
Why does HA filler last several months to a year, even though HA in the body breaks down so fast?
Because of a process called crosslinking. Natural HA breaks down within a few hours to a day, but in filler the HA molecules are "linked" together into a 3D net using a linking agent called BDDE, which makes the body's enzymes break it down much more slowly. The more crosslinking, the stronger and longer-lasting the filler — but choosing the right level of crosslinking for the job requires a doctor's judgment.
What is G prime, and what does it have to do with choosing filler?
G prime is the firmness or lifting-strength value of a filler. High-G-prime filler is firm and supports structure well, suiting work that needs standing and force-bearing, such as the chin, nasal bridge, and jawline. Low-G-prime filler is softer and smoother, suiting thin skin and areas that need a natural look, such as under-eyes and lips. Choosing the wrong value can make the result too firm or lumpy, so it's something the doctor must judge based on the area.
If I get HA filler and I'm not happy with it, can it be corrected?
Yes, it can. And this is the most important safety advantage of HA filler, because there's an agent called hyaluronidase that, once injected, helps dissolve HA filler faster. If the result is unsatisfactory, lumpy, asymmetric, or there's a complication, the doctor can use this agent to correct it — unlike permanent fillers or foreign substances, which are very hard to remove once injected.
How does HA filler differ from permanent filler or liquid silicone, and why is it safer?
HA filler is a substance the body already has and can break down on its own naturally; if you're not happy with it, there's an agent to dissolve it. Permanent filler, liquid silicone, or foreign substances injected into the face stay in the body forever; the body sees them as foreign, which can cause inflammation, hard lumps, and drooping with gravity over time, and they're very hard to remove, sometimes requiring surgery. So HA is safer and "reversible," while permanent substances are a hard-to-fix decision.
How do monophasic and biphasic fillers differ, and which should I choose?
They're different textures. Monophasic is a single, uniform, smooth gel that's easy to spread and gives smooth, even skin, suiting fine work like under-eyes and shallow nasolabial folds. Biphasic is a gel made of small particles dispersed in a carrier, usually giving good lifting support and structural standing, suiting structural augmentation that needs to stand up. Neither is "better" overall — it depends on the job, which is the doctor's role to choose appropriately.
Does HA filler really hold water? Does it make the face swell?
HA really does hold water, and very well. A single HA molecule can bind around 1,000 times its own weight in water. This is why it helps add volume and makes skin look hydrated. In the early period after injection there may be some swelling from water-binding and from the procedure itself. Filler shows a change in volume from the day it's injected, but the result truly settles after the swelling subsides, around 1 to 2 weeks.
How does Depry Clinic in Phitsanulok choose HA filler to suit our face?
Dr. Time first assesses your facial structure, skin thickness, and each person's goals, then chooses the filler type, G prime value, and crosslinking level suited to each area — for example, firm material to support structure for the chin and nose, soft smooth material for under-eyes and lips. We use only genuine, FDA-approved HA filler that can be inspected, and always explain things so you understand before deciding, with no course pushing.
References and verification
I'd like you to be able to verify the information I use yourself — these are the references this article draws from:
- U.S. Food and Drug Administration (FDA) — official information on dermal fillers as medical devices requiring approval, and why choosing the type/doctor matters. Used to support the points on safety and using genuine products: fda.gov — Dermal Fillers
- DermNet (NZ) — dermatological information on fillers, HA filler types compared with other types, and complications. Used to support the points on HA being dissolvable/reversible, unlike permanent substances: dermnetnz.org — Fillers
- Academic article (PMC) on hyaluronic acid in the skin — explains HA's water-binding property and its role in the skin. Used to support the points on HA being a natural substance in the body and the water-binding mechanism: PMC4174906 — Hyaluronic acid in skin
- Academic article (PMC) on HA fillers and their physical properties — explains crosslinking, G prime, and the differences between filler types. Used to support the points on choosing filler by area: PMC6489475 — HA filler properties
