Take formaldehyde as an example. Generally speaking, formaldehyde is a harmful gas to human body. Long-term inhalation of formaldehyde is not only easy to cause a series of respiratory diseases, but also lead to symptoms of formaldehyde poisoning, such as dizziness, pungent smell, tears and palpitations. When inhaled in high concentration, severe respiratory irritation and edema, eye irritation and headache may occur. Direct contact of formaldehyde with skin can cause allergic dermatitis, pigmentation and necrosis. Inhalation of high concentration formaldehyde can induce bronchial asthma.