What a Laser Actually Does to a Blood Vessel
A vascular laser does not vaporise the vessel and it does not burn it away. It heats the blood inside it until the vessel wall is damaged from within and the body clears the remains over the following weeks. Understanding that sequence explains the bruise that sometimes follows, why the result appears gradually rather than immediately, and why the same machine is set differently for a fine thread vein on a cheek and a birthmark on a child.
A laser aimed at a blood vessel does not vaporise it and does not burn it away. It heats the blood inside the vessel until the vessel wall is damaged from the inside, and then your body clears away the remains over the following weeks. Once you know that sequence, three things make sense: the bruise that sometimes follows, why the result appears slowly instead of straight away, and why the same machine is set up completely differently for a fine thread vein on a cheek and a birthmark on a child.
What a Laser Actually Does to a Blood Vessel: the essentials
The short version
Haemoglobin in the blood inside the vessel, not the vessel wall itself
The blood inside the vessel, not the wall of the vessel itself.
The blood absorbs the light, heats, and damages the vessel wall from within
The blood soaks up the light, gets hot, and damages the vessel wall from the inside.
At settings that rupture the vessel, blood escapes into the tissue and looks like a bruise
At settings strong enough to burst the vessel, blood leaks into the tissue, and that looks like a bruise.
The body has to clear the treated vessel, which takes weeks
Your body has to clear away the treated vessel, and that takes weeks.
A larger vessel needs a longer pulse to heat all the way through
A bigger vessel needs a longer flash to heat it all the way through.
Vessels vary in size and depth; one setting cannot suit all of them at once
Vessels come in different sizes and sit at different depths. One setting cannot suit them all at once.
Choosing a target by colour
Picking a target by its colour
Oxygenated haemoglobin absorbs light strongly in particular bands, notably around 418, 542 and 577 nanometres. A laser tuned near one of those peaks is absorbed far more by the blood in a vessel than by the surrounding skin, which is exactly the selectivity the treatment depends on.
The red pigment that carries oxygen in your blood soaks up light strongly at a few particular colours. A laser tuned close to one of those is soaked up far more by the blood inside a vessel than by the skin around it, and that is exactly the fussiness the whole treatment depends on.
The pulsed-dye laser, at 595 nanometres, sits deliberately just off the absorption peak. Being slightly off it means less energy is absorbed in the first fraction of a millimetre, so more of it reaches vessels deeper down. That is a design decision, not a compromise, and it is a good illustration of how carefully these machines are matched to the tissue.
One common vascular laser is deliberately tuned a little to one side of the strongest peak. Being slightly off means less of the energy is used up in the first fraction of a millimetre, so more of it gets down to the vessels sitting deeper. That is a design choice, not a compromise, and it is a good example of how carefully these machines are matched to real tissue.
Longer wavelengths, such as 1064 nanometres, are absorbed less by blood but penetrate deeper still, which makes them the choice for larger and deeper vessels, and for treating patients with more pigment in the skin, since that pigment also absorbs less at those wavelengths.
Other lasers use a longer wavelength, which blood soaks up less but which travels deeper still. That makes them the choice for bigger and deeper vessels, and for people with more colour in their skin, since that colour also soaks up less of this kind of light.
The part everyone forgets: time
The bit everyone forgets: time
Choosing the right colour is only half of it. The other half is how long the light is delivered. Every structure has a characteristic time over which it sheds heat, and it is roughly proportional to the square of its diameter. A small vessel cools quickly; a large one takes much longer.
Choosing the right colour of light is only half the job. The other half is how long the light is switched on for. Everything in your skin takes a certain amount of time to shed heat, and bigger things take much longer than small ones. A tiny vessel cools almost instantly. A large one takes far longer.
If the pulse is much shorter than that cooling time, energy is deposited faster than it can spread, and the vessel can rupture. That produces purpura, the deep bruise-like discolouration that some treatments deliberately aim for and others deliberately avoid. If the pulse is much longer, heat leaks into the surrounding tissue before the target is destroyed, and you risk a burn rather than a result.
If the flash is much shorter than that cooling time, the energy piles in faster than it can spread out, and the vessel can burst. That gives you the deep bruise like mark that some treatments aim for on purpose and others carefully avoid. If the flash is much longer, heat leaks out into the surrounding skin before the target is destroyed, and you risk a burn instead of a result.
So pulse duration is matched to vessel size. Fine facial telangiectasia and a thick leg vein are not the same problem, and setting the machine as though they were is how people end up with either no result or a mark. This is the technical content behind the phrase settings chosen for the individual, which otherwise sounds like sales language.
So the length of the flash is matched to the size of the vessel. A fine broken vein on a cheek and a thick vein on a leg are not the same problem, and setting the machine as if they were is how people end up with either no result or a mark. That is the real content behind the phrase settings chosen for you, which otherwise sounds like sales talk.
What happens over the following weeks
What happens over the following weeks
The treated vessel is damaged, not removed. Over the following days and weeks the body breaks down and clears the coagulated contents and the damaged wall, and the vessel is gradually resorbed. The visible improvement follows that clearance rather than the treatment.
The vessel is damaged, not removed. Over the following days and weeks your body breaks down and clears away the clotted contents and the damaged wall, and the vessel gradually disappears. The improvement you can see follows that clear up, not the appointment.
This is why patience is part of the protocol. Immediately after treatment the area may look worse: red, swollen, sometimes bruised. At two weeks it looks better than before. At six weeks it looks better again. Judging the result on the day is judging the injury, not the outcome.
This is why waiting is part of the plan. Straight after treatment the area can look worse: red, swollen, sometimes bruised. At two weeks it looks better than it did at the start. At six weeks it looks better again. Judging the result on the day is judging the injury, not the outcome.
It is also why a series is usual. A single pass treats the vessels that suited that day’s settings. Those that were deeper, larger or smaller may need a different setting, and vessels that were not fully destroyed can recanalise, which is to say reopen. Two to four sessions is a common course, and for a birthmark it can be considerably more.
It is also why a course is usual. One pass treats the vessels that suited that day’s settings. Ones that were deeper, bigger or smaller may need different settings, and vessels that were not completely destroyed can simply reopen. Two to four sessions is a common course, and for a birthmark it can be a great many more.
Where it goes wrong
Where it goes wrong
Almost always through competition for the light. The pigment in skin absorbs across a broad range, and it sits above every vessel being treated. Too much energy, insufficient cooling, or a tan, and the pigment absorbs enough to blister or to change colour, either lighter or darker.
Almost always because something else is competing for the light. The colour in your skin soaks up a wide range of light, and it sits above every vessel being treated. Too much energy, not enough cooling, or a tan, and that colour soaks up enough to blister the skin or leave it lighter or darker than before.
This is why the diagnosis has to come before the laser. Facial redness can be rosacea, sun damage, an inflammatory condition or something else entirely, and some of those need medical treatment rather than, or before, a laser. A vessel that is actually a different lesion is a diagnosis that a laser will not correct and may obscure.
This is why the diagnosis has to come before the laser. Redness on a face can be rosacea, sun damage, an inflamed skin condition, or something else entirely, and some of those need medical treatment instead of, or before, a laser. Something that looks like a vessel but is not is a diagnosis a laser will not fix, and may hide.
Questions patients ask
Will I have a bruise afterwards?
Will I have a bruise afterwards?
It depends on the settings. Some protocols deliberately produce purpura, a deep bruise-like mark lasting one to two weeks, because it can be more effective for certain lesions. Others are set to avoid it. It is a reasonable thing to ask about before booking around an event.
It depends on the settings. Some treatments deliberately produce a deep bruise like mark that lasts one to two weeks, because that can work better for certain marks. Others are set specifically to avoid it. It is a fair thing to ask about before booking around a wedding or a holiday.
Why do I need more than one session?
Why do I need more than one session?
Vessels vary in size and depth, and one set of parameters cannot treat all of them optimally. Some vessels also reopen after partial treatment. Most facial vascular courses run to two to four sessions, spaced several weeks apart.
Vessels differ in size and in how deep they sit, and one set of settings cannot treat all of them well. Some vessels also reopen after being partly treated. Most courses on the face run to two to four sessions, several weeks apart.
Will the veins come back?
Will the veins come back?
Treated vessels that are fully destroyed do not return, but the tendency that produced them usually remains. In rosacea in particular, new vessels can develop over time, and maintenance sessions are common.
Vessels that are completely destroyed do not come back, but whatever caused them usually has not gone away. With rosacea in particular, new vessels can appear over time, and top up sessions are common.
Can leg veins be treated the same way?
Can leg veins be treated the same way?
Small leg vessels can respond, but sclerotherapy is commonly first-line for them, and larger or bulging leg veins may reflect underlying venous disease that needs assessment before any cosmetic treatment.
Small leg vessels can respond. But for those, an injection treatment that closes the vein is usually tried first, and larger or bulging leg veins can be a sign of a problem in the deeper veins that needs checking before any cosmetic treatment at all.
Is it safe on darker skin?
Is it safe on darker skin?
It can be, with the right wavelength, appropriate settings and good cooling, but the margin is narrower because skin pigment competes for the light. Device choice and operator experience matter more here than anywhere else.
It can be, with the right kind of light, careful settings and good cooling. But there is less room for error, because the colour in your skin competes for the same light. The choice of machine and the experience of the operator matter more here than anywhere else.
Where to go next
Talk it through with a physician first.
Every plan starts with an assessment of your skin, your anatomy and what you actually want to change.
This page is general health information, not medical advice. It cannot tell you whether a treatment is right for you. Approved uses, risks and results differ from person to person, and product labelling changes. Ask us at Dermatology and Laser Centre about your own situation, or make an appointment, and seek urgent care for any serious symptom.
