Paradoxical hair growth
Dr Godfrey Town enlightens us on paradoxical hair growth, the evolution of hair removal home use devices and their impact on the professional marketplace
Paradoxical hair growth is the stimulation of hair growth in areas on, or adjacent to areas treated with hair removing laser, or intense pulsed light (IPL) devices. In a recent study with Peter Bjerring, I examined published reports of paradoxical hair growth, and reviewed the published scientific studies to identify any link between low fluence and the stimulation of paradoxical hair growth.
After entering the market in 2004, home use devices are now well established. One of the first—a laser and an IPL which was for use in the home—came from the British company, Dezac Group. This has progressed to IPLs and laser devices being available in Boots’ main stores, department stores and online. For hair removal, the majority in the UK are IPLs, although there is one very well known laser device apart from the Dezac product, which is the Tria Beauty laser.
People always assume that home use devices are low fluence. In fact, if you look at the parameters for the Tria Beauty laser, you’ll see that the range of fluences claimed by the manufacturer is 6-24 joules per sq. cm. Comparing that to the Lumenis Light Sheer ET professional laser, which was a very popular diode laser for several years—the range there is 10-40 Joules per sq. cm. When I compared the Asclepion MeDioStar with the Lightsheer ET in a study a few years ago, we were using fluences in our trials of 23 Joules per sq cm—a typical user fluence for a professional diode and what’s now achievable even with a home use device.
Ron Wheeland has published two prospective studies and produced very good data. He even managed to treat Fitzpatrick skin types five and six, and of course found that, he observed very strong reactions and a lot of hyperpigmentation. As a consequence of this research, he was able to say which consumers shouldn’t be allowed to treat themselves with these home use laser devices. Even in the absence of blinded controlled studies, we can conclude that the Tria Beauty home use device is clinically effective.
Research into paradoxical hair growth
Paradoxical hair growth has been attributed to low fluence at or near the periphery of the treatment area. In my research with Peter Bjerring, we first examined established scientific knowledge about the absorption and the scattering of light in tissue to test the theory. Then we examined scientific studies to see whether low fluence was the most probable cause of unwanted hair growth. Beginning with Igarashi’s very well-known diagram describing forward scattering of light in turbid tissue, the predominant direction of light going into tissue is forward scattering, and the majority of useful light does not travel laterally in tissue very far outside the contact area with the tissue.
Some of the work in my PhD examined distribution of light in mathematical simulations and this also confirmed that even when you apply very high concentrations of photons of light in the tissue, the majority of the light is forward scattering. Very little light moves laterally beyond 2 mm from the edge of the treatment area that is likely to have a biological impact, including stimulation of hair growth.
However, it should be noted that perilesional erythema and oedema is very commonly seen well outside of the 2 mm periphery of the treatment area, and it seems to be one of those cases where the answer is probably staring us in the face, but we’re not really looking at the most logical cause.
I performed some measurements on IPLs which all have a very large divergence angle of about 135 degrees. If you calculate the exponential loss of stray light energy from these devices, even using a high fluence IPL with a large spot size of 4.5 sq. cm., the energy at 5 cm distance away from that light source would be of the order of 0.5 mJ/cm2. One eminent researcher in the area of low level laser therapy pointed out to me that you’d need at least 80,000 times more energy than that to stimulate hair growth—so it’s a very, very low figure, and unlikely to be a cause of stimulation for hair growth 5 cm away.
I don’t deny that paradoxical hair growth exists. I’m just questioning whether or not it’s most likely cause is by low fluence light energy rather than some other origin.
Examining other causes
It’s important to take time to look at all causes for stimulation of regrowth of hair after light-based therapy, including other factors, completely unrelated to the treatment itself. These include seasonal variation in hair growth patterns, increases of hair growth with age, paradoxical effect of androgens, endocrine disorders, idiopathic hirsutism, stress, medications, use of anabolic steroids, food supplements, use of Minoxidil and exposure to UV light. All of these things can cause hair growth without it being related to the treatment by laser or IPL and most importantly, in the literature there are many references to acquired hypertrichosis associated with post-inflammatory traumatic and burn injury reactions. So we know that there are lots of reasons why we should be thinking about post-inflammatory reaction as a likely primary cause of this hair growth.
In our literature review we looked at the Thaysen-Petersen paper from 2011, where he found one controlled and six uncontrolled trials on home use devices looking at three different IPL sources and the diode laser. We also undertook a further search in 2014, and we performed a retrospective analysis of our own clinical study files—to try and identify published studies reporting paradoxical hair growth following professional and at-home treatments. We found no published studies documenting paradoxical hair growth from home based light based treatments. That doesn’t mean it doesn’t happen, but there’s nothing published so far.
We also know that there are recent studies showing that very low laser fluences are effective in hair reduction. I know that the published papers on the use of in motion technique using the diode laser talks about an average fluence in the order of 5-7 Joules per sq cm. That’s a fairly low fluence and we can’t say that those devices don’t work. It’s not logical to think those sort of fluences are going to be suitable for stimulating hair growth because they do produce stable hair growth reduction.
The Moreno-Arias paper, reported on paradoxical hair growth in five out of 49 females with polycystic ovarian syndrome following IPL photoepilation and skin rejuvenation treatment, and mentioned being about 5 cm away because he’d only treated the sideburns and the chin area of that patient, so there is classic paradoxical hair growth. I think we’d all agree that’s what it is. What’s causing it is the big question.
I don’t have the answer, but I’m trying to exclude unfounded excuses that could be made by professionals looking for reasons for advising clients not to buy one of those “cheap toys” from Boots, because “they don’t work and they can cause paradoxical hair growth”—which is what started this study in the first place. Although, I believe home use devices are more of an adjunctive or companion treatment, rather than any threat to professional treatments.
In 2002 Vlachos & Kontoes also found terminal hair growth several months after therapy. In these cases the cause of hair transformation to terminal hair could be explained by the inflammatory response. The paper makes an obvious point—it’s possible that inflammatory response would be a good reason for expecting that to happen.
In 2005, Kontoes also performed a retrospective study, looking back at 750 subjects out of a total of 4,374 treatments with an Alexandrite laser. All of these were quite dark-skinned type—Fitzpatrick three to four. Hair induction was recorded in 4% of the cases, and this hair regrowth, 3-24 months later, was noted after at least three treatments.
Several of the reviewed studies were retrospective, asking clients about hair growth or examining photographs after the event, then deciding afterwards whether they’re seeing paradoxical hair growth and then trying to extrapolate backwards whether they could have been caused by low fluence.
When we’re considering possible causes or paradoxical hair growth following laer or IPL treatment, I also think it’s very difficult when you’re treating people with PCOS. Hormones change and even if they had no treatment at all, they might have exhibited this kind of hair growth without having any laser or IPL treatment whatsoever.
Marayiannis et al. basically came up with the same thing—classic paradoxical hair growth. These authors very clearly said that there was a significant relationship between the hair induction that they saw and single episodes of severe erythema, hyperpigmentation or crusting. Once again, that was the main conclusion about the possibility of the cause of this paradoxical hair growth.
Barcaui had similar comments about his studies. He said sub-optimal fluence was an unlikely cause, while heat-induced inflammatory response to treatment may have played a role. Willey et al. had some interesting findings. They observed this paradoxical hair growth problem and made some suggestions about controlling it, including extensive use of cooling gel packs all around the treatment area. It may look rather strange for hair removal in an aesthetic clinic, but he did find that by chilling the surrounding tissue it prevented paradoxical hair growth from occurring. This is clearly preventing the erythema response, so I think probably we’re going down the same track with those suggestions.
It’s unlikely that hair growth several centimetres or more way from the irradiated skin surface can be attributed to scattered or stray optical radiation, the science doesn’t hold up for that. The incidence of true paradoxical hair growth is probably limited to darker skin photo types of specific ethnic origin. Typically it’s found in females of Middle Eastern or South Asian extract, clinically obese with evidence of underlying hormonal disorders and middle-aged PCOS, and there may be other androgen hormone irregularities, including, of course inflammatory sequelae.
Causes of stimulated hair growth
In our opinion, the observed perilesional inflammatory response is the most likely cause of hair growth stimulation. Certainly limited terminal hair growth reoccurring on the same body area treated previously with low fluence can hardly be seen at the same time as both the cause of subsequent extended hair growth delay and terminal hair regrowth. The two things just don’t hang together. And paradoxical hair growth does remain a rarely reported event.
Home use devices
Launched back in 2004, there are probably two or three million of these devices now in use worldwide. Europe is behind the USA and behind Asia in the use of these products, growing at about 16-18% per annum, whereas Asia is growing at over 30% per annum.
These devices have been developed with a whole range of safety features built into them: safety switches, capacitance sensors, low initial settings; and safe parameters for skin types are also determined by skin tone sensors. When placed on the surface of the skin, they read the melanin content in the skin in the area to be treated before you can fire the device. So not only can you not fire the device in free space, it will also evaluate the skin type for safe use.
It won’t work on a small body because of capacitance sensing, so the manufacturers have gone a long way to try and make these devices fool proof and child proof, and they’ve done that for a very simple reason—self-protection—they don’t want to be sued. So far there has only been one letter to the editor of the JADV Journal which has reported a single case of hyper pigmentation from somebody using one of these devices at home. There have been no other cases reported in the literature of adverse incidents, which is pretty incredible for several million devices sold already.
Several devices that didn’t initially get their FDA clearance in the States for use on the face have subsequently been cleared for sale for treatment below the nose. Outside of the USA they’ve been used on the face as well as the body since they were first launched.
Because of the safety features built into these devices, safety glasses are unnecessary—because you can’t fire them in free space, your eyes can’t be exposed to hazardous laser or IPL energy.
In 2014 there was a new edition of the IEC 60825 laser classification standard, which introduced the idea of a Class 1C laser—whereby you can embed a laser of higher class in a device whilst making that device effectively a Class 1 laser. Use of that standard is not possible however, unless there’s a corresponding vertical standard i.e. a product standard, to go with it. The first product standard recently passed into the final draft international standard (FDIS) stage. The international standard will be published by December 2015 and we shall see publication of that first standard in Europe by February 2016. This product standard contains the test methodology required that the manufacturers will have to follow. The ones I’ve mentioned have all been embodied in that standard so providing it’s adopted worldwide, hopefully we will not see any unsafe devices being launched.
From the manufacturers’ point of view they don’t want to “rock the boat” with the profession. They see these devices as a huge opportunity for partner products with existing treatments that professionals are carrying out e.g in hair reduction, after a series of six or eight treatments when there are a few rogue hairs that grow back and the patient returns, the availability of a device like this for top-up treatments at the end of their course means that they could do that treatment themselves.
Dr Godfrey Town is a registered clinical technologist and RPA2000 certificated laser protection adviser specialising in the comparative measurement of laser and IPL devices.
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