Methyl ethyl ketone (MEK) is a colorless liquid with a sweet/sharp, fragrant, acetone-like odor. It is an extremely flammable liquid and vapor. The vapor is heavier than air and may spread long distances and distant ignition and flashback are possible. MEK is highly volatile.
Methyl ethyl ketone occurs naturally in
volcanoes, forest and bush fires, products of biological degradation, and in
some foods. It is also found in motor vehicle exhaust. This is a high volume chemical with production
exceeding 1 million pounds annually in the
Electroplating machinery and repair;
Wood stains and varnishes.
Types of consumer products that may contain methyl ethyl ketone:
Acid nonhousehold metal cleaners (liquid);
Aerosol paint concentrates;
Auto, other transportation, and machinery refinish paints;
Automobile body polish and cleaners;
Ground/traffic marking coating;
Household hard surface cleaners (aerosol);
Household hard surface cleaners (liquid);
Household tints and dye;
Industrial particleboard (furniture, fixtures, cabinets, etc.);
Inks, writing and stamp pad inks (excl drawing and printing inks);
Laundry starch preparations;
Markers, fine point and broad tipped;
Miscellaneous use aromatics;
Miscellaneous agricultural/pesticidal products;
Miscellaneous paint-related products;
Nail enamel and polish removers;
Nonstructural caulking compounds and sealants;
Paint and varnish removers;
Shoe polishes and cleaners;
Solvent thinned interior clear finishes;
Solvent thinned interior stains;
Solvent thinned interior undercoaters and primers;
Specialty performance sealants;
Surfactants, finishing agents, and assistants;
Synthetic resin and rubber adhesives;
Routes of exposure: dermal, inhalation, oral.
MEK absorbed primarily via inhalation.
Target organs: CNS, mucous membranes, upper respiratory tract, eyes, skin.
The effect of acute exposure depends on extent and duration of exposure.
MEK is a mucous membrane and upper airway irritant. Brief exposures (3-5 minute) to its vapors produces slight nose and throat irritation at 100 ppm. The vapor has a strong odor and irritating effects at 350 ppm. 143 volunteers exposed to 200 ppm for 4 hours reported throat irritation, unpleasant odor, nausea, and headache (in order of frequency reported). Higher exposures are expected to cause central nervous system depression with symptoms such as headache, nausea, dizziness, drowsiness, and confusion. Extremely high concentrations may cause loss of consciousness and possibly death.
Acute inhalation exposure resulted in eye, nose and throat irritation, nausea, headache, vertigo, loss of coordination, CNS depression. With prenarcotic and narcotic symptoms, tachycardia and cardio-respiratory failure can occur. In most cases recovery is usually rapid and complete.
Acute inhalation tests in rats indicate low toxicity from methyl ethyl ketone exposure via inhalation.
Splash contact and vapors cause irritation and lacrimation of eyes.
Dermatitis has been reported in humans following dermal exposure to methyl ethyl ketone. Oral ingestion of MEK is expected to cause central nervous system depression with symptoms such as headache, nausea, dizziness, drowsiness, and confusion. Extremely high concentrations may cause loss of consciousness and possibly death. Swallowing or vomiting of the liquid may result in aspiration into the lungs.
Limited information is available on the chronic effects of MEK in humans from inhalation exposure. One study reported nerve damage in individuals who sniffed a glue thinner containing MEK and other chemicals. Slight neurological, liver, kidney, and respiratory effects have been reported in chronic inhalation studies of methyl ethyl ketone in animals., 
MEK has been reported to
cause peripheral and central neurotoxicity following long-term exposure. The
Repeated or prolonged contact can produce dermatitis.
No information on the reproductive or developmental effects of methyl ethyl ketone in humans was located. An inhalation study in mice exposed to MEK reported decreased fetal weight and fetal malformations. Developmental effects have also been reported in rats following oral and inhalation exposures. [EPA]
No studies were available on the carcinogenicity of methyl ethyl ketone by the oral or inhalation routes. In a dermal carcinogenicity study, skin tumors were not reported from methyl ethyl ketone exposure. [EPA]
The results suggest that occupational exposure to organic solvents, mainly n-hexane, toluene, MEK and FA, may cause cytogenetic damage in buccal cells and that use of exfoliated buccal cells seems to be appropriate to measure exposure to organic solvents.
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 .. Xiao JQ, Levin SM: The diagnosis and management of solvent-related Disorders. Am J Ind Med Jan 37 (1):44-61, 2000.
 . Mitran E, Callender T, Ohra B, et al.: Neurotoxicity associated with occupational exposure to acetone, Methyl Ethyl Ketone, and Cyclohexanone. Environ Res 73, 181-188, 1997.