The article quotes the authors saying, "Hyperpigmentation, when the skin's cells increase their production of the brown or black pigment melanin, is the most common adverse effect of laser treatments in dark-skinned individuals. It is not life-threatening, but postinflammatory hyperpigmentation may cause substantial psychological problems. The treatment of postinflammatory hyperpigmentation is difficult and time-consuming, often lasting many months to achieve the desired results, which causes frustration in patients and physicians." Some clinicians have hypothesized that skin cooling, which decreases pain and allows the use of higher laser frequencies, could also reduce hyperpigmentation after laser treatment.
Woraphong Manuskiatti, M.D., and colleagues at Mahidol University, Bangkok, Thailand, used laser irradiation (from a 1,064-nanometer Q-switched Nd:YAG laser) to treat 23 Thai women (average age 43) with Hori nevus, blue-brown pigmented spots on the skin that develop later in life. "One randomly selected face side of each patient was cooled using a cold air cooling device during and 30 seconds before and after laser irradiation, and the other side was irradiated without cooling," the authors write. Two dermatologists not involved in treatment examined digital photographs to measure the occurrence of hyperpigmentation before treatment and one, two, three, four and 12 weeks after treatment.
Of the 21 patients who completed the study, 13 (62 percent) developed hyperpigmentation on the cooled side, five (24 percent) developed it on the uncooled side, one patient (5 percent) developed it on both sides and two (10 percent) did not experience any hyperpigmentation. The cooled sides were three times more likely to become hyperpigmented after laser treatment than the uncooled sides. Most (62 percent) of the cases of hyperpigmentation developed two weeks after treatment, and all but one case completely resolved 12 weeks after treatment.
All patients showed less than 25 percent lightening of their Hori nevi at 12 weeks post-treatment. "No difference in clinical improvement was observed regarding the cooling used on one side during treatment," the authors write.
It is unclear why cold air cooling would increase the risk of hyperpigmentation following laser treatment, but skin cells may have reacted to the combination of laser treatment and cold air, the authors note. "Future studies should address the question of whether the other methods of epidermal cooling are associated with an increased risk of postinflammatory hyperpigmentation," they conclude.