Ethyl methacrylate (EMA) is the chief chemical used to produce artificial nails. Methyl methacrylate (MMA), a similar chemical, was banned by the U.S. Food and Drug Administration in 1974 after it proved harmful to nail technicians and clients. However, illegal MMA use continues, especially in salons that offer low prices for acrylic nails, as MMA costs much less than EMA. Both chemicals have low odor thresholds, meaning that most people can smell them at low levels. These chemicals can also irritate the eyes, nose, and other mucous membranes and cause skin irritation, skin inflammation and asthma in some people. Like EMA and MMA, exposure to acetone, another chemical commonly used in nail salons, can also irritate the eyes, nose, and throat. Acetone can also dry the skin, and upon repeated contact can result in skin irritation and inflammation. At higher concentrations, acetone can affect the nervous system and may cause drowsiness or sleepiness. Like EMA, acetone has a low odor threshold (approximately 2 parts per million), well below the NIOSH Recommended Exposure Limit, a criterion set up to protect workers from harmful exposures.