(Methanal; 37% aqueous solution (usually containing 10 to 15% methanol) is called formalin; solid polymer is called paraformaldehyde)

CAS 50-00-0





Physical Properties

Clear, colorless liquid

Formaldehyde: bp -19 °C, mp -92 °C

Formalin: bp 96 °C, mp -15 °C

Miscible with water



Pungent odor detectable at 1 ppm


Vapor Density

~1 (air = 1.0)


Vapor Pressure

Formaldehyde: 10 mmHg at -88 °C Formalin: 23 to 26 mmHg at 25 °C


Flash Point

50 °C for formalin containing 15% methanol


Autoignition Temperature

424 °C for formalin containing 15% methanol


Toxicity Data

LD50 oral (rat)

500 mg/kg


LD50 skin (rabbit)

270 mg/kg


LC50 inhal (rat)

203 mg/m3 (2 h)



1 ppm (1.5 mg/m3)



0.3 ppm (ceiling)(0.37 mg/m3)



2 ppm (2.5 mg/m3)

Major Hazards

Probable human carcinogen (OSHA "select carcinogen"); moderate acute toxicity; skin sensitizer.


Formaldehyde is moderately toxic by skin contact and inhalation. Exposure to formaldehyde gas can cause irritation of the eyes and respiratory tract, coughing, dry throat, tightening of the chest, headache, a sensation of pressure in the head, and palpitations of the heart. Exposure to 0.1 to 5 ppm causes irritation of the eyes, nose, and throat; above 10 ppm severe lacrimation occurs, burning in the nose and throat is experienced, and breathing becomes difficult. Acute exposure to concentrations above 25 ppm can cause serious injury, including fatal pulmonary edema. Formaldehyde has low acute toxicity via the oral route. Ingestion can cause irritation of the mouth, throat, and stomach, nausea, vomiting, convulsions, and coma. An oral dose of 30 to 100 mL of 37% formalin can be fatal in humans. Formalin solutions can cause severe eye burns and loss of vision. Eye contact may lead to delayed effects that are not appreciably eased by eye washing.

The National Academies | 500 Fifth St. N.W. | Washington, D.C. 20001
Copyright © National Academy of Sciences. All rights reserved.
Terms of Use and Privacy Statement