Cooling method may halt hair stimulation after laser treatment

The review of 543 patients with Fitzpatrick skin types II, III and IV, treated between December 1998 and December 2003 at a clinic in Spain, contradicts much conventional wisdom regarding hair stimulation following photo-epilation, says Andrea Willey, M.D., clinical instructor, dermatology, Oregon Health & Science University and a study co-author.

"It's actually thought to be quite rare," with low reported incidence rates focusing mainly on patients of Mediterranean descent, Dr. Willey tells Dermatology Times.

The study

To better understand the problem's incidence and potential causes, owners of the Dermitek Clinic in Bilbao, Spain, enlisted Dr. Willey's help in performing a retrospective chart review on all patients who received laser and IPL photo-epilation at this facility over a five-year period. Investigators reviewed digital and other patient images before and after treatment, as well as medical histories.

Treating physicians used a long-pulsed 755 nm alexandrite laser (Gentlelase, Candela) in 85 percent of cases, an IPL source (Epilight, Lumenis) in 10 percent and a 1,064 nm Nd:YAG laser (Lyra, Laserscope) in 5 percent. Treated areas included the beard, neck and chin, excluding the upper lip. Patients received between three and 23 treatments, with treatments usually performed every two to three months.

Results

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 (Willey A et al. Lasers Surg Med. 2007 Apr;39(4):297-301).

"Hair growth stimulation occurs both within the treated area and, interestingly, it can also happen in the surrounding untreated area," Dr. Willey says.

Regarding causes of hair growth stimulation, she says, "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."

Other factors associated with failure to epilate and risk of hair stimulation include hair color, Dr. Willey says. Because photo-epilation absorbs melanin within melanocytes of treated follicles, dark hair heats up more efficiently than lighter hair and is probably easier to thermally injure, she explains.

Depth of treated hair might also play a role, Dr. Willey says. In this regard, she says light sources may not penetrate sufficiently to adequately injure deeply growing anagen hairs in some areas. However, the study data didn't prove or disprove this hypothesis, she notes.

Dr. Willey adds that in the review, terminal hair growth occurred most frequently in the low maxillary or "beard" area, as well as the neck, lateral cheeks and chin areas.

Whatever its causes, treating hair growth stimulation presents challenges, Dr. Willey says.

Though the hairs that grow post-treatment are thicker and darker than the vellus hairs originally treated, she explains, "They're still not thick and dark enough to easily get rid of. That's the problem."

Once patients start experiencing hair growth stimulation, Dr. Willey says, "then it becomes very difficult to treat."

Therefore, researchers offer a photo-epilation protocol aimed at preventing hair growth stimulation.

For starters, Dr. Willey says, "If one uses high enough energies during hair laser treatment, one might be able to prevent hair growth stimulation within the treated area."