These two treat different layers and different problems, so they are less alternatives than they look. Ultherapy focuses ultrasound to a point beneath the surface, as deep as the SMAS, without touching the skin at all. A fractional CO2 laser does the opposite: it resurfaces the surface itself, in a pattern of tiny columns, to change texture and colour.
That means each one is useless at the other's job. Ultherapy does nothing for surface texture, brown patches or fine crepey skin quality, because it deliberately spares the epidermis and everything between the transducer and the focal point. CO2 resurfacing works at and just below the surface, so it does not act on the deep layer a lax jawline or neck comes from.
Downtime is the second axis, and the gap is large. Ultherapy has essentially none: transient redness, swelling and tenderness, occasionally bruising or temporary numbness. Ablative resurfacing has a genuine recovery. We could not find a published figure for how long that recovery lasts, so no number is quoted here. What is published is a same-patient comparison: in a split-face trial, fractional CO2 produced longer redness, pain, swelling and scab-detachment times than the non-ablative arm. Ask the clinic performing it for their own expected timeline, in writing. Ask the clinic performing it for theirs, in writing.
CO2's risk profile deserves plain description rather than a footnote. Pigment change after treatment is the main one. In a same-patient stretch-mark study, post-inflammatory hyperpigmentation appeared on 6 of 10 CO2-treated sides, against 4 of 10 on the radiofrequency-treated sides of the same abdomens. In a split-face acne-scar trial, fractional CO2 produced significantly more pigment events than the non-ablative comparator, along with longer redness, pain, swelling and scabbing. Loss of pigment - skin going lighter rather than darker - also appears among ablative-laser complications serious enough to reach a specialist referral clinic. How often that happens, and how long it lasts, is not quantified in the published literature, so no figure is given.
Real-time ultrasound imaging lets the operator see the tissue plane before firing.
Untreated skin is deliberately left between the columns, which is what "fractional" means and what makes healing faster than treating the whole surface at once.
At the focus, tissue reaches roughly 60 to 70 degrees Celsius, creating small columns of denatured collagen. The surface and everything above the focus are spared. Healing contracts and remodels those points over two to six months.
The surrounding untreated skin supplies the cells that resurface the treated columns. New collagen forms as those columns heal.
The deepest reaches the SMAS, the layer surgeons lift in a facelift. Imaging is separately cleared to visualise up to 8 mm below the surface.
We could not find published depth figures for CO2 devices, so none are quoted. Depth varies by machine and by settings, which is a question for the operator.
Granted through a De Novo request (DEN080006, 11 September 2009); the arms and abdomen wording was added in February 2025 (K243035).
We were not able to confirm the exact clearance wording for individual CO2 lasers, so no clearance number and no indication list is quoted for them here. Ask which device is being used and what its cleared text says.
Not a labelled figure - downtime is not stated in the Indications for Use.
There is no published duration for CO2 recovery, so none is stated. What it does record is that in a same-patient trial, ablative fractional CO2 produced longer redness, pain, swelling and scab-detachment times than a non-ablative comparator. Get the clinic's expected timeline in writing before booking.
Ablative resurfacing carries more pigmentary risk than non-ablative treatments, and more in deeper skin tones. This is not a reason to rule it out - it is a reason to have a specific conversation before booking rather than after.
Two published same-patient comparisons are the clearest evidence available. In a stretch-mark study of 10 people who completed treatment, hyperpigmentation appeared on 6 of 10 fractional CO2-treated sides and 4 of 10 radiofrequency microneedling sides, mostly resolving by the three-month follow-up. In a split-face acne-scar trial of 30 people who completed, CO2 produced significantly more pigment events than the non-ablative arm. Neither study is large, and both were comparing CO2 with something else rather than measuring CO2 on its own.
Loss of pigment is the other side of this, and it is the one people are least warned about. Post-inflammatory hypopigmentation - patches of skin that go lighter than the surrounding skin - appears among the complications documented in a review of 25 patients referred to a specialist clinic after procedures performed by experienced cosmetic physicians, alongside hypertrophic and atrophic scarring. That review was a single centre with no denominator, so it tells you the complication happens, not how often. When lighter patches do occur they can be slow to change, and there is no reliable treatment for them. Ask specifically about hypopigmentation risk for your skin tone, and ask for a test area.
Ultherapy does not carry this particular risk profile, because it does not injure the surface. Its documented rare events are different: transient motor nerve injury, including the marginal mandibular and frontal branches, and subcutaneous fat atrophy.
Cold-sore reactivation after ablative laser resurfacing is well documented, and antiviral cover started in advance is standard practice for it. That is why a cold-sore history has to be disclosed at the point of booking, not on the day and not afterwards.
If you get cold sores, say so when you book. Antiviral medicine is started before the appointment, so it has to be prescribed in advance. This matters most for CO2 resurfacing, where reactivation is well documented and prophylaxis is routine. Tell your provider even if you are booking Ultherapy - it is their call to make, and they need the information beforehand.
Before ablative resurfacing, also expect to discuss your skin tone and pigment history, any recent tanning, and what happens to your skin after inflammation such as spots or scratches. Ask for a test area if you have a deeper skin tone.
Resurfaced skin is an open wound while it heals, and infection is the reason to seek urgent care rather than wait for a routine appointment. Go now if you have: