Hyaluronic acid (HA) is a sugar molecule that belongs to the glycosaminoglycans family. Its superpower is that it attracts and retains water like a molecular sponge; a single molecule can hold up to 1000 times its weight in water.

It is not foreign to you: you have it in your skin (for hydration and volume), in your joints (as a lubricant and shock absorber), in your eyes (maintaining the shape of the vitreous humour), in cartilage and even in the umbilical cord.

Hyaluronic acid is present in multiple tissues:

• Skin: in the dermis, providing hydration and volume
• Joints: as a lubricant and shock absorber (synovial fluid)
• Eyes: in the vitreous humour, maintaining the shape of the eyeball
• Cartilage: as a structural component
• Umbilical cord: in high concentrations

The problem is that from age 25-30, your internal factory starts producing less. By age 40 you have half the HA you had at 20, and by age 60 less than 25%. This is why hollow under-eye circles, sagging and wrinkles appear.

Because natural HA degrades in less than 48 hours. Natural HA has a half-life in the skin of approximately one day. If you were injected with unmodified HA, it would disappear within hours.

Decades ago, it was extracted from rooster combs, but this caused many allergies due to avian proteins and required a huge number of animals for very little product.

Today, aesthetic HA is manufactured in laboratories through bacterial fermentation. The result is chemically identical to human HA, but standardised and purified.

This is where the magic of chemistry comes in. Lab-produced HA undergoes a process called cross-linking.

Imagine a plate of loose spaghetti (your natural HA); if you throw them against the wall, they fall. Now imagine tying those spaghetti strands together with small glue bridges (a chemical agent called BDDE). You get a stiff three-dimensional network. That is cross-linked HA. These chemical bridges make the filler resist attacks from your enzymes and last for months.

Cross-linking is what differentiates a long-lasting filler from a short-lived product.

BDDE (butanediol diglycidyl ether) is the most widely used cross-linking agent in the manufacture of hyaluronic acid fillers. It is a molecule that creates bridges between HA chains to form a three-dimensional network.

In quality products, BDDE is almost completely eliminated during the purification process, leaving only insignificant traces. Manufacturers invest millions to ensure the final product is safe and biocompatible.

Most adverse reactions are not to the HA itself, but to traces of the cross-linker, residual bacterial proteins or lidocaine (the local anaesthetic included in many syringes).

Absolutely not. Each area requires a different consistency:

• Lips: Soft HA that integrates well when speaking or kissing
• Tear troughs (under-eye hollows): Very fluid and soft HA for a delicate area
• Cheeks: Dense HA with strength to lift drooping tissue
• Jawline: Ultra-dense HA to define hard lines and provide structure

Using the wrong product is like trying to build a wall with jelly or filling an under-eye hollow with cement.

No. Skinboosters are lightly cross-linked (very fluid) HA that is injected in a distributed pattern (multiple micro-points) to deeply hydrate the skin. They do not lift folds or enlarge lips; their function is to give the skin quality, luminosity and that "glow" texture.

They last between 3 and 6 months. Examples of brands: Profhilo, Restylane Skinboosters, Juvederm Hydrate.

Yes. Each manufacturer has its own "secret recipe" for cross-linking and proprietary technology:

• Juvederm (Allergan): VYCROSS technology (high duration and lift) and VYCROSS 17 (softer)
• Restylane (Galderma): NASHA technology (more natural, less swelling)
• Teosyal (Teoxane): RHA range (Resilient Hyaluronic Acid) that adapts to areas that move a lot
• Belotero (Merz): CPM technology (Cohesive Polydensified Matrix), ideal for very thin skin

Price differences reflect years of R&D investment, safety and predictability. Not all syringes are equal.

It works through a dual mechanism:

• Direct volume: it occupies the hollow space under the wrinkle and pushes the skin upwards
• Hydration: it attracts water, which slightly swells the tissue and fills from within

This happens because the molecule has chemical groups (carboxyl and hydroxyl) that form hydrogen bonds with water, trapping it around.

Yes, but it's temporary and normal. By attracting so much water, the area may look fuller or shinier for the first 48-72 hours. After a week, this localised fluid retention subsides and stabilises.

The famous "Pillow Face" only appears if the doctor injects excessive amounts or uses poor technique, not from the natural hydration of the product.

It depends on your metabolism, the product and the area:

• Lips: 6-9 months (they are in constant motion and the skin is very thin)
• Nasolabial folds: 9-12 months
• Tear troughs: 9-12 months
• Cheeks and jawline: 12-18 months (or more)
• Skinboosters: 3-6 months

Thin skin and areas of high movement accelerate the body's "consumption" of the product.

Avoid smoking: tobacco generates free radicals that reduce HA duration by up to 30% and damages your skin quality.

Also accelerates absorption:

• Daily extreme sports
• Frequent saunas (increases body temperature and metabolism)

Drinking more or less water does not affect the filler, nor do facial creams.

It is extremely rare because the molecule is identical to your own. If a reaction occurs, it is almost never to the HA itself, but to:

• Lidocaine (the anaesthetic included in many syringes)
• Traces of the cross-linking agent (BDDE)
• Residual bacterial proteins from the fermentation process

If you are allergic to lidocaine, the doctor will simply use HA without anaesthetic.

It's not rejection like an implant. HA degrades naturally through the action of the body's endogenous hyaluronidases.

However, if late inflammation (weeks later) appears, it could be:

• Inflammatory nodules (immune system reaction)
• Biofilm (a mild bacterial infection around the gel)

These are treated with corticosteroids or by dissolving the product with hyaluronidase.

Good quality HA does not calcify. If a patient develops hard lumps years later, the most likely causes are:

• They were injected with a permanent filler disguised as HA (silicone, PMMA or calcium hydroxyapatite)
• The product was of dubious quality (black market)
• A fibrotic nodule formed (excessive body response)

If it is genuine HA, it dissolves within hours with hyaluronidase.

This is called the Tyndall effect. The Tyndall effect is a physical phenomenon of light scattering that occurs when a light beam passes through colloidal particles. In aesthetic medicine, it occurs when HA is injected too superficially in the dermis (especially in the thin skin of the eye contour).

Light scatters as it passes through the gel and gives a bluish, greyish or whitish colour (depending on skin thickness and product amount). It is very typical of poorly performed tear trough filler.

Solution: dissolve the superficial layer with hyaluronidase and re-inject at the correct depth.

Hyaluronidase is an enzyme (a protein) that degrades hyaluronic acid by breaking the glycosidic bonds between its disaccharide units. It is injected into the same area as the filler and, within 24-48 hours, the product disappears.

In aesthetic medicine, the "off-label" use of hyaluronidase is considered the gold standard for managing complications associated with HA fillers, including vascular occlusion. It is the "magic eraser" of aesthetics.

Side effects: it hurts a bit more than filler (burns for a minute). The enzyme does not distinguish between clinic-injected HA and your own natural HA, so the skin in the area may become slightly drier or thinner for 2-4 weeks until your body regenerates its own HA.

Warning: recent applications of hyaluronidase (e.g., multiple sessions to dissolve fillers in large volumes) have been associated with a risk of lipoatrophy (localised fat loss). It is recommended to use it with caution and at the minimum effective doses.

Hyaluronidases are naturally found in many organisms:

• Mammalian testes (bovine, ovine): the traditional source and the most clinically used
• Snake, lizard and insect venoms: contribute to local damage and toxin spread
• Bacteria (such as Staphylococcus aureus): produced as a virulence factor to penetrate tissues
• Human cells: PH-20 is a testis-specific hyaluronidase, essential for fertilisation

Today there are also recombinant synthetic hyaluronidases produced by bacterial fermentation.

First 24-48 hours:

• Forget makeup (risk of infection through open microchannels)
• Do not rub or massage the area (you could displace the product)
• Zero alcohol (increases bruising and swelling)
• No intense exercise, heat (sauna, direct sun, tanning bed) or extreme cold
• Sleep face up the first night (to avoid crushing the gel that hasn't settled yet)
• If you need to see the dentist, try to postpone it for at least a couple of weeks (mouth retractors can deform lip filler)
• If you are pregnant or breastfeeding, it's better to wait (no safety studies)

No. When HA is absorbed, your face returns exactly to its previous state, not a worse one.

What happens is psychological: you get used to seeing yourself with volume and when it disappears, the contrast makes you feel like you look worse. Physically, the only exception is if you have been injecting huge amounts for years; the skin may have stretched a little, and when the filler is removed it may be slightly looser, but this is not the skin "falling" from using hyaluronic acid.

The famous "duck lip" effect (lips everted outward and exaggerated) is the result of malpractice. It happens due to:

• Injecting too much volume at once (more than 1.5 ml in one session)
• Using HA that is too dense (cheek filler doesn't belong in lips)
• Injecting only the border and not the body of the lip
• Accumulating layer after layer of product over the years without dissolving previous filler

A good professional aims for natural results: they prefer to inject 0.5 ml and see you back in three weeks to assess if you need more, rather than filling all at once. A natural result makes people say "you look great!", not "what have you done to your lips?".

No. The breast needs a large volume (between 100 and 300 ml per side). Injecting that much HA would cost a fortune (each syringe is 1 ml) and would be extremely dangerous due to the risk of nodules and infection. For the breast, there is surgery or lipofilling.

It also does not work for filling stretch marks (its effect is very limited) nor for removing pigmented dark circles: HA fills the hollow, but does not lighten the purple or brown colour of the skin (which is due to vascularity or melanin).

Price varies depending on area and brand:

• Skinbooster: £180-300
• Lips (1 ml, good brand): £220-400
• Cheeks: £300-550
• Jawline: £350-650

If you see a clinic offering hyaluronic acid for less than £130 per syringe, be suspicious. Premium brands cost more because they invest millions in safety, purity and cross-linking technologies that prevent the gel from moving or forming lumps.

The price difference also reflects the doctor's experience, location and guarantees.

Demand to see the box. The doctor must take out the sealed packaging in front of you before opening it.

Check that:

• The seal is intact (not previously opened)
• It has the manufacturer's security hologram (Allergan, Galderma, Merz, Teoxane...)
• The lot number and expiry date are visible

And remember: legally, in the UK and almost all of Europe, only a registered doctor can inject you. If you are being treated by an aesthetician, you are in a place of professional intrusion. Run away.

A sugar molecule naturally present in our body, capable of holding up to 1000 times its weight in water. In aesthetics, it is used to hydrate and fill.

It is produced in the laboratory through bacterial fermentation, but it is chemically identical to human HA. It is no longer extracted from animals (rooster combs).

Botox relaxes muscles to prevent expression lines. Hyaluronic acid fills, hydrates and adds volume. They are complementary.

Because it is cross-linked, a chemical process that binds its molecules together to make them resistant to the body's natural degradation.

It depends on the area: 6-9 months for lips, 9-12 months for folds and tear troughs, and 12-18 months for cheeks or jawline.

It is a tolerable discomfort. Today, almost all fillers include lidocaine (anaesthetic) and topical anaesthetic cream can be applied beforehand.

Yes, quickly and almost completely by injecting an enzyme called hyaluronidase. It disappears within 24-48 hours.

Only for the first 48-72 hours due to water attraction. Then the swelling subsides and stabilises.

No. The molecule is too large to penetrate the skin. Creams hydrate the surface, but do not replace injections.

They may have beneficial effects for joint health, but they do not fill wrinkles or add volume to the skin. The amount reaching the skin is minimal.

Not recommended during pregnancy or breastfeeding. There are no safety studies.

No. Legally, only a registered doctor can do it. Professional intrusion is dangerous and has caused numerous serious complications.