Pelleve and Ultherapy. If these lasers burn off underlying fat, how will new collagen form?

Thank you for your question. You are asking if Pelleve and Ultherapy burn underlying fat, how can they cause collagen to form. You indicate knowing about reviews where underlying facial fat loss was lost with laser treatment, making people look gaunt, and asking if the body can still generate collagen after 70.
I can certainly give you some guidance about collagen induction treatments, even without a photo, and in the absence of a physical exam. I’m Dr. Amiya Prasad. I’m a Board Certified Cosmetic Surgeon and Fellowship-trained Oculoplastic Surgeon. I own several types of lasers, as well as Pelleve, microneedling, and perform collagen induction treatments regularly in my practice. I also perform collagen induction therapy without heat, using platelet-rich plasma, as well as skin boosting.
To first clarify, Pelleve and Ultherapy are not lasers, but they do use the same principle of heat induction to stimulate collagen. Pelleve generates heat gradually using radiofrequency (RF) waves, which is appropriate for darker skin that would otherwise be prone to hyperpigmentation if a laser was used. Ultherapy is a high frequency ultrasound (HIFU) device that heats suddenly. The sudden heating and lack of temperature control is why I don’t use Ultherapy in my practice. There are various types of lasers like CO2, Erbium, and Nd:YAG, that can either ablate or remove the top layer of skin, or partially ablate which is otherwise known as fractional laser. Other lasers like Q Switch and the FRAC3 setting of an Nd:YAG laser can generate heat without ablation. The purpose of generating heat is to create a controlled injury, where the body responds by producing collagen at the dermis level, or the backbone of the skin. Heat also creates a skin tightening effect. Collagen can be stimulated at a specific temperature, without causing fat loss if that temperature is maintained, not exceeded, and the temperature is not held too long.
Fat loss is caused by overheating the skin through prolonged exposure to heat, or overexposure where the temperature is too high. Many people try to avoid surgery like facelifts, thinking the skin tightening effects of laser, radiofrequency, and ultrasound devices can replace surgery. When one tries to stimulate more collagen than the body can produce, or get greater tightening effect than is safe, heat exposure below the dermis at the fat layer is prolonged or excessive, so fat loss occurs.
Think of the different thermal devices as tools, and their correct use, or misuse is at the hands of the doctor. Often, thermal devices are applied by non-physicians as many states including New York where I practice does not have laws to limit these devices to doctors only. If these devices are used properly, collagen can be stimulated, and skin tightening achieved. However, the body’s ability to generate collagen is limited, so trying to generate more collagen, or trying to get even tighter skin can cause overexposure. Fat loss is not caused by these devices, because fat loss can be avoided when they are used judiciously. Fat loss is caused by the person handling the device, and also by the patient insisting on results that cannot be safely achieved, like non-surgical skin lifting, or more collagen than the body can produce.
The body’s ability to generate collagen is limited, so time is needed between heat treatments. To avoid too much heat exposure that can affect the fat layer, I also use platelet-rich plasma (PRP) to stimulate collagen without heat. PRP is made up of the concentrated wound healing and growth factors present in one’s own blood, which is drawn like a blood test, and spun to concentrate the platelets. I often apply PRP in between thermal treatments for additional collagen stimulation. PRP can also be applied with hyaluronic acid using the skin booster device, which does not harm the skin, and also doesn’t use heat.
It’s important to meet with doctors who can explain the limits of collagen induction, so they do not overtreat the skin and cause fat loss. Also, ask prospective doctors about other collagen induction treatments that don’t use heat to avoid excessive heat exposure and fat loss. I hope you found this information helpful. Thank you for your question.

Pelleve is NOT a laser and DOES NOT destroy fat.  It takes 20 to 25 minutes of sustained heating to destroy fat cells.  Pelleve treatments only sustain heat in the treatment area for 3-5 minutes.  It is a great non-invasive treatment that is safe for all skin types.  Bulk RF heating causes some of the existing collagen to collapse, stimulating your body to generate new replacement collagen.  Since it is not a laser, it is safe for all skin types and can be done safely year round.  It feels like a warm rock massage.  Collagen building takes 90 to 120 days to see the results, so be patient.  We recommend 1 treatment per decade.  In your 70's, we would suggest a series of 7 treatments spaced 4 weeks apart.  You will continue to build collagen for up to 6 months after the last treatment.  Best of luck.