Paradoxical laser hair stimulation (hypertrichosis) is a very real phenomena whereby laser application that would usually reduce the amount of hair actually causes stronger regrowth. How could this happen? How often does this happen and what are the risks?

Can Laser Hair Removal Stimulate Growth?

Yes, in a rare number of cases laser hair removal can stimulate growth. While we don't yet know the exact reason for this, there are enough cases where this has happened for it to be a recognised problem with laser hair removal.

The official term for hair growth stimulation resulting from laser hair removal treatment is hypertrichosis​.

How Often Does it Occur? Study 1 - Less than 1% Incident Rate There haven't been many studies looking at Paradoxical laser hair stimulation. However, one particular study looked at the effects of laser hair removal at one particular clinic on 489 patients. Out of these 489 patients, exactly 3 patients experienced what was deemed to be paradoxical laser hair stimulation. "Of 489 patients, 3 (0.6%, 95% confidence interval: 0.01-1.9%) treated with the long-pulsed alexandrite laser (755 nm) reported increased hair after laser hair epilation." Source: Alajlan A, Shapiro J, Rivers JK, MacDonald N, Wiggin J, Lui H : Paradoxical Hypertrichosis after Laser Epilation (2005) Study 2 - 10.5% Incident Rate Yet, in another study, the incident rate was much higher than this. 543 patients were treated at the same laser hair removal clinic in Spain and while 80% of the patients noticed substantial hair reduction, 10.5% reported laser induced hair growth. "While nearly 80 percent of patients saw some hair reduction with ongoing treatment, around 8 percent showed no improvement, and 10.5 percent experienced increased hair growth versus baseline" Source: Willey A et al. Lasers Surg Med. 2007 Apr;39(4):297-301 This is the problem with scientific studies - it's never matter of fact, rather quite messy, with a large number of variables that come into play. What we can say for sure is that the phenomenon is rare and most people won't experience it.

Profile of the 3 Patients that Experienced Hair Stimulation in the Scientific Study

Out of the 489 people that were involved in this laser hair removal study, 3 people reported hair growth stimulation. These are their profiles:-

Profile 1- 21 Year Old Man ​ This patient was a 21 year old Chinese man with black hair. The man noticed an increase in the amount of hair after 11 days of the laser hair removal session

Profile 2 - 39 Year Old Woman ​ This patient was a 39 year old Mediterranean woman with black hair. As is common with all the patients, initially the woman noticed that the laser hair removal yielded positive results yet after a certain period of time (this was undisclosed in the study) she noticed significant hair regrowth on the treatment areas. ​

Profile 3 - 30 Year Old Man ​ This patient was a 30 year old white man with black hair on both his arms and his back. The first three laser hair removal sessions yielded a positive result however after six sessions the hair started to regrow. ​ The hair regrowth was only noticed in the areas where he was receiving laser hair removal treatment.

Who is Likely to Experience Paradoxical Laser Hair Stimulation? ​We don't have a definite profile of people, however from the study mentioned above the three people all had the same Fitzpatricks skin type (IV). The other commonality was that all patients had black hair. It should be mentioned that the incidence rate for this study was so low that we cannot draw any firm conclusions about who this phenomena may affect.​

Why Does Laser Induced Growth Occur?

The Current Scientific Theory

We don't have scientific proof as to why laser induced hair growth occurs, however the most popular theory is that certain types of hair, known as "vellus hairs", are stimulated into growth by the light from the laser.

The sub-therapeutic affect of the laser stimulates these hairs into growth making them thicker and longer. However, even though the hairs that grow post-treatment are thicker and darker than the vellus hairs originally treated they're still not thick and dark enough to easily get rid of.

This is why further treatments with laser hair removal on areas that have laser induced growth doesn't work.​

Reports of Hypertrichosis from Other Sources The great thing about the internet is that anyone can contribute to the discussion and share their experiences. There are a number of internet forums related to laser hair removal where consumers have described how laser induced hair growth has occurred for them: "The first time I noticed the adverse reactions of the ipl was when I went in for my very first test patch on the back of my shoulder where the hair was light and sparse. ​ Soon after the test patch area grew back it came out thicker and darker and I remeber looking in the mirror comparing both sides of my shoulder thinking "those dark hairs were never there before and why are they only on the one side of my shoulder in the test patch area" and wondering if the ipl did this." "I am new to this website & wish I had read this before I went for laser hair removal. I am a fair skinned, dark haired woman with excessive hair growth. ​ I believe I'm type III. It's mainly vellus hairs over my entire body, but they are noticeable since the hairs are dark. I started getting laser done on my side burns in April 2005 and went until March 07 - with about 6 weeks between treatments. ​ It worked great on the side burns. But then the vellus hairs on my cheeks, adjacent to where the side burns started growing longer and darker. It also was growing along my jaw line."

Conclusions We Can Draw from all the Evidence

In the face of a severe lack of scientific data, we have to draw our own conclusions based on the evidence that is available.

Here are our conclusions from looking at the limited scientific data, listening to professional electrologists / laser hair removal specialists and reading reports from consumers online:-

Often occurs in some areas - Hypertrichosis resulting from laser hair removal occurs mainly in facial areas for women and on the back, shoulders and upper arms for men.

- Hypertrichosis resulting from laser hair removal occurs mainly in facial areas for women and on the back, shoulders and upper arms for men. Doesn't occur in other areas - There are hardly any reports of laser-induced stimulation on the bikini line, lower legs or underarms. These areas appear to be "immune" to this kind of risk

- There are hardly any reports of laser-induced stimulation on the bikini line, lower legs or underarms. These areas appear to be "immune" to this kind of risk Frequency is low - The scientific study shows that the frequency of this occuring is as low as < %1. However, professional laser hair removal practitioners and electrologists "believe" that this figure is too low. This is based on personal experiences rather than any scientific data, though, so these reports have to be taken with a pinch of salt.

- The scientific study shows that the frequency of this occuring is as low as < %1. However, professional laser hair removal practitioners and electrologists "believe" that this figure is too low. This is based on personal experiences rather than any scientific data, though, so these reports have to be taken with a pinch of salt. Occurs mainly on darker skin types - It appears that this pheneomena is more prevalent on those with darker skin types. For example, in the study, it only occurred on people with a Fitzpatrick rating of 4.

- It appears that this pheneomena is more prevalent on those with darker skin types. For example, in the study, it only occurred on people with a Fitzpatrick rating of 4. Further laser treatment doesn't stop the growth - from the numerous reports of this happening online, it seems that further laser hair removal treatments don't prevent the growth. In most cases, patients will need to resort to electrolysis hair removal in order to remove hair that has been stimulated by a laser.

- from the numerous reports of this happening online, it seems that further laser hair removal treatments don't prevent the growth. In most cases, patients will need to resort to electrolysis hair removal in order to remove hair that has been stimulated by a laser. Usually occurs when the patient has Vellus hairs - here is an extract from a study surrounding laser hair stimatulation:-



"Somehow when the follicle is stimulated by subtherapeutic thermal injury, it causes the hairs to become thicker and longer. And we believe this occurs in people who have prominent vellus hairs to begin with."