Skin Cooling During Laser Treatment Backfires

BANGKOK, Thailand, Sept. 17 -- Cooling the skin to protect it from hyperpigmentation after laser treatment actually increased discoloration in dark-skinned patients, researchers reported.

In a split-face study of Asian patients with mole-like skin lesions, the side of the face treated with cold air along with laser therapy was almost three times more likely to develop hyperpigmentation than the uncooled side, Woraphong Manuskiatti, M.D., of Mahidol University here, and colleagues reported in the September issue of Archives of Dermatology.

Post-inflammatory hyperpigmentation is probably the most common adverse effect of laser treatment in dark-skinned individuals with acquired bilateral nevus of OTA-like macules, or Hori nevus, the researchers wrote.

Hori nevus is characterized by blue-brown spots occurring bilaterally on the forehead, temples, eyelids, malar, and nasal areas. These nevi tend to occur later in life, mainly in women, and have been successfully treated with Q-switched nd:YAG lasers.

However, transient hyperpigmentation occurs in 50% to 73% of patients after laser treatment. Some clinicians have hypothesized that skin cooling, which decreases pain and allows safer and high laser frequencies, could also reduce hyperpigmentation, the researchers wrote.

The study included 21 Thai women (mean age 43) with bilateral Hori nevi treated on both sides of the face with a 1064-nm Q-switched Nd:Yag laser at an average of 7.0 J/cm² using a 3-mm spot size. One randomly selected face side was treated with a cool-air device 30 seconds before, during, and 30 seconds after laser irradiation.

Post-inflammatory hyperpigmentation was evaluated by measuring the melanin index and was clinically assessed by two non-treating physicians before treatment and once weekly for four weeks after treatment.

Of the 21 patients, 13 (62%) developed hyperpigmentation on the cooled side, compared with only five (24%) on the uncooled side.

One patient had hyperpigmentation on both the cooled and uncooled sides, and two (10%) did not develop hyperpigmentation

The cooled sides were almost three times more likely than the uncooled sides to develop hyperpigmentation after laser treatment (relative risk, 2.6; 95% confidence interval, 1.13-6.00; P=0.03). The clinical evaluation corresponded to the spectrometer reading, the researchers said.

Most of the hyperpigmentation cases developed two weeks after treatment. The onset at week 1, 2, 3, and 4 was 5% (1/21), 62% (13/21), 14% (3/21), and 10% (2/21) of the patients, respectively.

Post-inflammatory hyperpigmentation resolved completely 12 weeks after laser treatment in all the patients except one with skin type IV, who developed hyperpigmentation on the cooled side.

All the patients showed less than 25% overall lightening of the Hori nevi at week 12, the researchers reported. Overall clinical improvement was not affected by whether cooling was applied, the researchers said.

At baseline, there was no significant difference in the melanin-index values of the cooled and uncooled sides (P=0.17.) At week 12 there was also no difference in the index values of the lesions in either the cooled and uncooled sides.

However, the melanin index of all areas considered to have post-inflammatory hyperpigmentation was significantly increased compared with baseline (P=0.03), the researchers reported.

It is unlikely that cold air alone is the cause of the inflammatory effects, Dr. Manuskiatti said. In an earlier test, two patients with untreated Hori nevus given cooling on one side of the face but no laser treatment did not develop discoloration on the cooled side.

The underlying mechanisms for developing hyperpigmentation after laser treatment are not well understood, the researchers wrote. It is possible, they said, that laser-irradiated melanocytes or keratinocytes (active in regulating melanogenesis) may become more hyperactive with stimuli such a cold temperature.

Future studies should address the question of whether other methods of epidermal cooling are associated with an increased risk of hyperpigmentation, as well as the underlying mechanisms, the researchers said.