Type of gas that causes irritation to eyes and cause difficulty to breath. This is one of the factors that causes sick house syndrome. Formaldehyde is the simplest aldehyde and is also known by its systematic name methanol. A gas at room temperature, formaldehyde is colorless and has a characteristic pungent, irritating odor. In view of its widespread use, toxicity and volatility, exposure to formaldehyde is a significant consideration for human health.