Skin-tightening treatments: what do they do to the tissues?

How Heat-Based Tightening Works

What focused ultrasound, radiofrequency and subdermal laser have in common is heat. Thread lifts and injectable treatments, by contrast, work through other mechanisms, not heat; even so, they are often discussed alongside these methods at a consultation.

Collagen, which forms the supporting structure of the skin, is a heat-sensitive protein. When it is heated in a controlled way, the hydrogen bonds in its triple-helix structure break, and the fibre shortens and thickens. This is the first response, and it is seen in the tissue straight away.

The second response comes later. The controlled damage caused by the heat starts a wound-healing process: fibroblasts (the cells that make collagen) are stimulated, and the production of new collagen and elastin and the formation of new blood vessels begin. Studies report that this later response matures over the following months, not within days. So with heat-based treatments, part of the effect appears at the time of treatment and part appears in the period that follows.

What sets the heat-based treatments apart from one another is where the heat is delivered and how it is distributed.

What Focused Ultrasound Does

Focused ultrasound concentrates sound waves at a specific point beneath the surface of the skin. At this focal point the energy turns into heat and leaves separate, millimetre-sized points of heat in the tissue. This controlled heat damage starts collagen remodelling; collagen production and the reorganisation of elastin then follow.

This is also what makes the method point-based: it does not heat a large area evenly from end to end, but creates separate points of stimulation at a set depth.

The depth of the focal point is not fixed; the target layer depends on the device and the handpiece (transducer) used. Research also shows that energy settings and patient selection criteria in this field have not yet been standardised. For this reason, it would be misleading to give a single depth or temperature that applies to all devices.

What Radiofrequency Does

With radiofrequency (RF), heat is not applied from outside; it is generated inside the tissue. An electric current passing through the tissue meets the tissue’s resistance, and this resistance turns the current into heat. Because each tissue has a different resistance, where the heat builds up also varies from tissue to tissue.

How the heat spreads depends on how the circuit is set up. In a monopolar set-up, the current enters through an active electrode, passes through the body and leaves through a passive electrode, so it travels through a larger volume of tissue. In a bipolar set-up, both electrodes sit on the surface of the skin; the current forms a closed circuit between them and stays in an area close to the surface. In the third set-up, microneedling RF, an array of needle-tipped electrodes carries the energy directly into the dermis, the layer beneath the skin’s surface layer; here the mechanical effect of the needles and the effect of the heat work together.

These are different circuit arrangements for the same job, and the difference between them is where the heat goes. The research does not allow us to say, in a single sentence, that one set-up is better than another.

What Subdermal Laser Does

In some laser treatments, the energy is delivered from beneath the skin rather than through its surface. The aim is to take the heat directly to the deep layer without passing it through the layers in between.

Studies report that laser energy delivered under the skin acts in two places at once: in the fatty tissue it disrupts the integrity of the cells, and in the lower dermis it causes collagen to contract and then starts a repair process that leads to the production of new collagen and elastin.

What sets this method apart from those applied to the surface is this: the skin has to be opened for the energy to reach the tissue. In other words, it is an invasive procedure. Anaesthesia, the risks of the procedure and the recovery period each need to be discussed separately; these are determined at a consultation.

Researchers also point to the method’s limits: it is still an open question how much tightening can be expected at each degree of laxity, and how reproducible the results are.

How Mechanical Support Works

A thread lift works not through heat but by repositioning the tissue. This is also what sets it apart from the other methods: no energy is delivered to the tissue; the tissue is moved.

Here the effect is mechanical. To counter sagging in the face, the thread is placed along lines that will lift the superficial musculoaponeurotic system, or SMAS (the layer of connective tissue that covers the facial muscles). The barbs on the thread grip the tissue, and the structure that has descended is moved upwards. The effect comes from the thread carrying the load, not from a healing response lasting weeks, as with heat-based treatments.

Some sources also mention changes that develop over time in the tissue around the thread; this possible second effect and its limits are covered in the guide on what lifting threads do in the tissues.

The method also has limits. Research in this field has reported high rates of repeat procedures (revisions) and complications with early treatments that used permanent (non-absorbable) barbed threads. Techniques developed with absorbable (dissolvable) threads were found to cause fewer adverse effects; however, the long-term effectiveness of these techniques remains unclear. More studies are needed to assess safety and long-term effectiveness more reliably. A thread lift also does not remove excess skin: if the main problem is excess skin, moving the tissue does not get rid of it. Because of this uncertainty in the long-term data, it would not be accurate to state how long the result lasts for any type of thread.

How Injectable Treatments Work

Injectable treatments are not a single group; they work on at least two different principles.

The first is adding volume. Hyaluronic acid (HA) fillers take up space in the layer they are injected into and support the tissue above. The effect appears as soon as the substance is placed.

The second is stimulating the tissue. Substances such as poly-L-lactic acid (PLLA), calcium hydroxylapatite (CaHA) and polycaprolactone (PCL) act like a scaffold in the tissue and trigger the person’s own collagen production. Some of them work through a controlled foreign body reaction, which starts a repair process led by macrophages (immune cells involved in repair); calcium hydroxylapatite, on the other hand, stimulates fibroblasts through mechanical tension. What they have in common is that the effect develops gradually, not straight away: studies report that collagen build-up starts within weeks and continues for months.

This distinction matters in practice, because the two groups do not target the same finding: one replaces lost volume, while the other tries to change the tissue’s own structure. Which substance is used, and in which layer, is decided at a consultation.

Which Findings Point to Which Treatment

Choosing a method starts not with the method but with the findings at the consultation. The ageing face is assessed layer by layer: skin quality, volume changes in the superficial and deep fat compartments (fat pads), the condition of the ligaments and the bony support, and displacement of the tissue. All of these layers change over time, but not at the same rate; which one stands out differs from person to person. The starting point of the plan is to tell volume loss apart from tissue displacement and skin laxity.

This assessment separates three distinct patterns, and each one points in a different direction.

If skin laxity and reduced tissue quality are to the fore – in other words, if the real issue is the firmness of the tissue itself rather than a displaced mass of tissue – heat-based treatments are considered.

If volume loss is to the fore – in other words, if fullness has decreased and contours have sunk inwards – injectable treatments that replace lost volume or stimulate the person’s own collagen production are considered.

If downward displacement of tissue is to the fore – in other words, if the sagging is clearly visible as a mass – thread lift methods that reposition the tissue are considered. If advanced sagging and marked excess skin occur together, surgery is the most comprehensive option in structural terms; research shows that in this pattern, non-surgical methods are not enough on their own.

In most faces, these three patterns are not seen on their own; they overlap. Which one is dominant in your case can only be determined at a consultation. Your doctor assesses you; the decision is yours.

Limits of These Treatments

Research has clearly set out the limits of these methods. Reviews of radiofrequency show that energy-based treatments do not match the results achieved with surgery, and that results are modest and not always predictable. The response is better in mild and moderate laxity; in advanced sagging and marked excess skin, an energy-based treatment on its own is unlikely to meet expectations.

The second limit concerns the field itself. Research on focused ultrasound shows that energy settings and patient selection criteria have not yet been standardised, and that long-term effectiveness needs more research. This does not mean that the method is ineffective; it means that there is not yet a single rule for which setting produces how much response, and in whom.

The third limit is individual. The same set-up with the same settings does not produce the same response in two different people; the response depends on the structure of collagen, which changes with age, on skin thickness and on general health. Thin skin in older age, certain autoimmune diseases (conditions in which the immune system turns against the body’s own tissues) and smoking are listed among the factors that affect the response.

The fourth limit concerns the scope of this information: knowing how the methods work does not tell you which one is suitable for whom. Suitability can only be determined at a consultation.

Treatments Offered Here

The clinic carries out mechanical thread lifts and injectable treatments. Which of these is considered for you is assessed at a consultation, based on which of the patterns described above is dominant in your case.