AS more women began clamoring for the latest sensation in hair care, the so-called Brazilian hair-relaxing treatments, the Neil George Salon in Beverly Hills, Calif., added a cabana with open sides and a fabric roof to isolate the process from the salon itself. “I couldn’t stand the fumes,” said Neil Weisberg, an owner.

Mark Garrison, the owner of a salon on the Upper East Side of Manhattan that bears his name, set aside a floor for the treatment, equipped it with special ventilators and began providing industrial-strength respirators to his clients and stylists. And a West Hollywood salon, John Frieda, relegated its straightening treatments to an open-air courtyard.

Just like the permanents that were once the height of fashion, the lucrative process of converting frizzy or kinky hair into smooth locks produces unpleasant odors. But is it dangerous, especially to the operators who apply the product repeatedly?

Last month, the beauty world was rattled when the occupational health agency in Oregon found significant levels of formaldehyde in the hair-smoothing solution sold under the name Brazilian Blowout. (A common ingredient found in many products, formaldehyde is a recognized carcinogen if it is present at high levels.) The agency said it had conducted lab tests after receiving numerous complaints from stylists citing nosebleeds, breathing problems and eye irritation after applying the product. Last Friday, Oregon authorities broadened their warning to include other hair-smoothing products, particularly those described as “keratin-based,” and said employers should take steps to protect their workers.