The HIFUis internationally recognized as the gold standard for non-invasive skin lifting. Focused ultrasound non-invasive anti-aging technology was invented by Ulthera in the United States in 2007 and entered the European market in 2008. In 2009, it received FDA approval in the United States, becoming a leading non-invasive treatment for skin lifting and anti-aging.
The American Ulthera HIFU device has three treatment cartridge depths: 4.5 mm (targeting the SMAS layer), 3.0 mm (targeting the fat layer), and 1.5 mm (targeting the dermis). Korean HIFU devices and Chinese domestic “Ultraboost” (by different manufacturers) also offer 1.0 mm and 2.0 mm cartridges, which target the dermis as well.
The ultrasound hifu’s cartridges create Thermal Coagulation Points (TCPs) at different skin depths—also known as thermal injury points or thermal damage zones. These TCPs are generated by high-energy focused ultrasound, causing immediate contraction of collagen fibers and stimulating new collagen production, which lifts and tightens the skin.
At the Thermal Coagulation Points (TCPs), the working temperature of the HIFU is around 65-70°C, which is about 5-10°C higher on average than Thermage. In theory, this means the HIFU causes more tissue damage (due to the higher temperature), and at the same time, more collagen is produced through the “damage and repair” mechanism.
Although both are non-invasive anti-aging treatments, their adverse reactions differ significantly because of the differences in device principles. Below is an introduction to the common and rare adverse reactions of HIFU, along with preventive measures.
Side Effects of HIFU Treatment
1. Linear ridges: Linear ridges are the most common reaction seen with HIFU treatments. These ridges are essentially a wheal-like reaction (similar to hives) caused by energy being delivered too superficially. They’re more likely to appear in areas where the subcutaneous tissue is thin and less resilient, such as the neck.
On the face, linear ridges typically result from high energy settings, poor skin tolerance, or inadequate contact between the treatment head and the skin. Mild linear ridges usually resolve on their own within 1-3 days. If significant redness and swelling occur, applying a topical corticosteroid ointment to the affected area can help reduce the reaction more quickly.
2。 Delayed linear ridges: Bright red linear ridges occur when heat is released into the superficial skin layers (epidermis and upper dermis). In contrast, delayed linear ridges with less severe redness and swelling result from heat being released into deeper layers (deep dermis, fat layer, and SMAS).
The formation of these ridges is likely related to excessively high energy density そして too many pulses in the same area. These ridges tend to resolve slowly and carry a risk of skin depressions. The possible causes of skin depression include fat atrophy and scar formation, though these cases are rare.
3。 Tissue swelling: The SMAS layer can become swollen under the high energy of focused ultrasound, typically without causing skin redness. This usually resolves within a week. This swelling is often why some patients feel their face looks wider after the procedure.
4。 Burns: Research has shown that the depth and location of the thermal coagulation zones created by HIFU are key factors determining both the occurrence of adverse reactions and the achievement of desired clinical results. Skin thickness varies between individuals and even in different areas of the same person. For example, facial skin is thicker than neck skin, with the cheeks being the thickest part of the face, followed by the forehead. Areas with thinner skin are more prone to burns. Burns can present as blisters (superficial second-degree burns) or ulcers (deep second-degree burns).
If blisters occur and are managed promptly and appropriately, they can completely resolve without leaving scars. However, if they are not managed correctly, there is a risk of scarring, which can also depend on whether the patient has a tendency for keloid or hypertrophic scarring.
In cases of ulcers, even with timely management, scarring is inevitable.
5。 Fat melting: HIFU is not intended for fat melting, but it can occur if the energy is too high or if there is excessive overlap of treatment lines (pulses). This risk is particularly pronounced in severely overweight individuals (those with a BMI indicating obesity), as their fat cells are more sensitive to heat.
To reduce the risk of burns, make sure that the treatment head is in good contact with the skin during the procedure. Check that the energy lines displayed on the treatment head align well with the skin. If the treatment head does not adhere properly to the skin, it can lead to burns, although this is quite rare.
6. injury: Research has confirmed that using HIFU in areas where nerves run close to the skin carries a risk of nerve injury. Therefore, it is essential to mark the treatment areas carefully and avoid working in high-risk zones. When treatments are performed outside of these danger zones, the risk of nerve injury is minimal. Another major risk factor is using high-energy settings or overlapping treatment lines.
Nerve injuries caused by HIFU are reversible. Recovery from facial motor or sensory nerve issues typically ranges from a few days to several months, with an average recovery time of 3.5 months. For patients with mild nerve injury, close monitoring and follow-up are usually sufficient, with no special treatment required. If there is significant swelling along with signs of nerve injury (such as tingling, numbness, or delayed motor function), a short course of oral or topical corticosteroids can be helpful. Additionally, nerve-nourishing agents like methylcobalamin can be used as supportive treatments.
HIFU treatment marking design and danger zones
Doctors experienced in performing HIFU treatments understand that there is a risk of nerve injury, so it’s important to first mark the treatment areas to avoid these high-risk zones. The official recommended marking design is shown in the following diagram, with red areas indicating restricted zones.
注記： The red areas in the diagram represent the no-treatment zones (danger zones).
No-treatment zones (danger zones)
The thermal damage caused by HIFU typically only transmits to the level of the SMAS layer. However, the average depth of facial nerves is usually deeper than the SMAS fascia layer. The temporal branch of the facial nerve, the marginal mandibular branch, and the supraorbital nerve all run relatively superficially and are at higher risk of injury. Therefore, the corresponding areas of the face are designated as no-treatment zones.
Additionally, all deep-penetrating skin rejuvenation devices should avoid the thyroid region. Doctors should strictly follow the treatment manual for marking and must not perform treatment in these restricted areas.
Indications:
- Eyebrow lifting
- Lifting sagging submental (under-chin) tissue
- Improving fine lines and wrinkles on the chest
- Neck tissue lifting (less effective for individuals with BMI > 30)
禁忌
- Open wounds on the face
- Severe cystic acne
- Presence of cardiac pacemakers, defibrillators, or metal implants in the treatment area
- Treatment is prohibited along the mandibular border
- Not recommended for individuals with a history of keloids
- Pregnancy
まとめ
1️⃣ Focused ultrasound anti-aging devices (including the American Ultherapy and domestic ultrasound devices) mainly target the SMAS layer, fat layer, and deep to mid-dermis, without damaging the epidermis. With standardized operation, adverse reactions are rare.
2️⃣ The adverse reactions presented in this article are mostly uncommon. Proper use and patient selection can largely prevent these rare adverse reactions.
3️⃣ According to published data, the adverse reaction rate of American Ultherapy is about 0.2%, including:
- Known transient effects like swelling and bruising (0.07%)
- Nerve involvement (temporary numbness or sensory/motor nerve issues, 0.07%)
- Nodules (0.02%)
- Blisters or epidermal burns (0.02%)
- Post-inflammatory hyperpigmentation (0.002%)
Rare adverse reactions such as nerve irritation, numbness, or sensory disturbances occur in less than 0.4% of cases.
4️⃣ The most concerning adverse reaction is nerve injury. In reality, the risk of nerve damage is low and typically reversible.
5️⃣ Preventative measures include:
✅ Strictly standardized operation — avoid overlapping multiple passes in one area
✅ Accurate treatment line mapping — avoid working in restricted areas
✅ Thorough assessment of relative and absolute contraindications — avoid treatment if absolute contraindications exist
✅ If adverse reactions occur, prompt and proper management can minimize severity
6️⃣ Irreversible adverse reactions for focused ultrasound devices mainly include scarring and skin depressions.
- Scarring is caused by high energy and overlapping passes leading to second-degree burns.
- Skin depressions are closely related to fat atrophy (lipolysis). For patients with severe obesity (fat cells are more sensitive to heat) or pre-existing facial indentations, extra care is essential to avoid these areas.
- Avoid overlapping passes in small areas to prevent localized overheating.
7️⃣ Domestic ultrasound devices share the same principle as the American Ultherapy device, so their potential adverse reactions should be considered similarly.
8️⃣ Although domestic focused ultrasound devices theoretically have lower energy output than the American Ultherapy, caution is still warranted.
- These devices have only been on the market for a short time, so there is little published data on adverse reactions. However, the absence of reports does not mean adverse reactions do not occur.
- Focused ultrasound can create thermal injury zones of 65–70°C in the skin — 5–10°C higher than Thermage. Theoretically, the higher the temperature, the greater the damage.
Thermage and Ultherapy, as high-temperature anti-aging treatments, can achieve “controlled” thermal injury when performed properly and according to guidelines. This means the heat-induced damage is fully repairable. However, if operation is not standardized and tissue temperatures become too high, the damage may be excessive and not fully reversible. Such irreversible damage is more likely with ultrasound devices (because of the higher temperatures they generate within skin tissues). Therefore, aesthetic practitioners must approach these treatments with great care and respect, ensuring precise and standardized operation of focused ultrasound devices.
