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About 37 percent of homes built four to five years ago have a higher concentration of a chemical that apparently causes the so-called sick building syndrome, according to the results of a study conducted by the Infrastructure Ministry.

Formaldehyde has been blamed for inducing headaches, dizziness and nausea in occupants of houses inflicted with the syndrome. The limit on formaldehyde concentration stipulated by the Health, Labor and Welfare Ministry is 0.08 parts per million.

According to the survey conducted by the Land, Infrastructure and Transport Ministry, 36.7 percent of houses built four to five years ago exceed the Health Ministry’s limit on the chemical. On average, 27.3 percent of houses exceed the ministry limit, while 28.8 percent of homes built within the past year and 28.9 percent of houses built in the past two to three years also surpass the figure, the survey shows.

Although the exact causes of sick building syndrome have yet to be determined, formaldehyde — frequently used in wallpaper glue — is one of the substances that apparently contributes to the problem.

Under the first large-scale study on sick building syndrome in Japan, conducted between September and March, the ministry obtained effective data on 4,476 homes, the ministry said.

The ministry looked at four chemical substances used in building materials and found there was a high proportion of houses that exceeded health safety limits.

“In terms of formaldehyde, there was a high proportion surpassing the limit, and we need to place priority on tackling the problem,” a ministry official said.

The ministry found that in an effort to respond to sick building syndrome, contractors suddenly began using materials that emit only low levels of chemicals. This resulted in housing built within the past three years having relatively low concentrations of problematic chemicals.

However, the concentration of formaldehyde was highest in houses built four to five years back, with the concentrations fading with the passage of time.

The higher the room temperature, the higher the concentrations became. Airtight buildings and units situated in higher areas that received several hours of sunshine a day also had higher concentrations of the chemical.

The average concentration of formaldehyde was 0.071 ppm, according to the study. While this figure is lower than the Health Ministry’s limit, 1,224 houses surpassed it.

The average concentrations of toluene, xylene and ethyl benzene were all below their respective limits, the study shows.

Of the housing studied, 12.3 percent surpassed the limit for toluene, while only 0.13 percent exceeded the figure for xylene.

Not much difference was observed between condominiums and houses, and there was a tendency for concentrations to be lower if the homes were well-ventilated, the study found.

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