In humans, transient and reversible sensory irritation of the eyes and respiratory tract has been observed in clinical
studies and epidemiological surveys. Odour threshold for most people ranges between 0.5 and 1 ppm. In general,eye irritation, the most sensitive endpoint, is associated with airborne concentrations beginning in the range of 0.3 to0.5 ppm. Eye irritation does not become significant until about 1 ppm, and rapidly subsides. Moderate to severe eye,nose and throat irritation occurs at 2 to 3 ppm. Sensory irritation has also been reported at lower exposure levels, but is then difficult to distinguish from background. Most studies show no effect on lung function in either asthmatics or non-asthmatics. Formaldehyde causes skin irritation and has corrosive properties when ingested. In some individuals, contact dermatitis may occur at challenge concentrations as low as 30 ppm.