OVERVIEW

What is formaldehyde poisoning?

Formaldehyde poisoning refers to a condition caused by either a single exposure to a large amount (which could be as little as a few milliliters) or long-term exposure to small doses of formaldehyde. Symptoms include lethargy, difficulty breathing, skin allergies, eye pain and tearing, and in severe cases, coma or even death.

The culprit, formaldehyde (also known as methanal), is a colorless, flammable gas with a strong, pungent odor. Its chemical formula is HCHO, and it is soluble in water or alcohol. A 34%–38% aqueous solution is known as formalin. Just 10–20 ml (about one tablespoon) of formalin solution can be fatal.

Is formaldehyde poisoning common?

The incidence of formaldehyde poisoning is relatively low.

What are the toxic effects of formaldehyde?

Formaldehyde is a protoplasmic poison (protoplasm refers to the living material within cells).

As a protoplasmic poison, it directly damages cells. After entering the body, formaldehyde primarily harms DNA, causing mutations, and disrupts proteins, interfering with normal cellular metabolism. It also strongly irritates the skin and mucous membranes (e.g., eyes, respiratory tract, and digestive tract), leading to swelling and increased secretions in these tissues.

The human olfactory threshold for formaldehyde is 0.06–1.2 mg/m³. At airborne concentrations of 1.2 mg/m³, its odor becomes detectable. Symptoms like eye pain and tearing begin at 0.01–1.9 mg/m³ (though individual sensitivity varies). Ingesting 10–20 ml of formaldehyde can be fatal.

Indoor formaldehyde levels of 30 mg/m³ can cause immediate death.

Specific toxic effects include:

• Effects on skin and mucous membranes:

  • Formaldehyde can cause skin allergies, inhibit sweat secretion (preventing sweating), and with prolonged exposure, lead to dryness, cracking, redness, eczema, itching, and even tissue necrosis, fissures, or tumors at the contact site.
  • It strongly irritates the eyes, nasal passages, and mucous membranes, causing swelling (e.g., puffy eyes, redness, excessive tearing or nasal discharge), laryngeal edema (difficulty breathing, throat swelling, choking), and coughing. Severe cases may result in nasal cancer.

• Neurotoxicity: Studies confirm formaldehyde damages brain neurons, leading to dizziness, impaired memory (e.g., story recall, visual memory, number retention), attention, visual perception, hand movement speed, and dexterity. Prolonged exposure worsens these effects, potentially causing dementia or coma. Chronic exposure also increases fatigue, depression, and anxiety, with some research suggesting mood alterations.

• Reproductive toxicity: Chinese studies on rats show formaldehyde harms reproductive systems and offspring development.

• Cardiovascular toxicity: Research indicates formaldehyde can cause bradycardia and P-wave disappearance, confirming its cardiovascular damage.

How is formaldehyde metabolized in the body?

Formaldehyde is readily absorbed through the respiratory and gastrointestinal tracts, with minimal skin absorption. Once absorbed, it oxidizes into formic acid, most of which further oxidizes into carbon dioxide and is exhaled. A small amount is excreted as formate in urine.

Absorbed formaldehyde directly invades cells, damaging them or binding to biomolecules to harm tissues. Some breaks down into methanol, which harms the nervous system (especially the optic nerves).

Chronic exposure to formaldehyde solutions may cause cancer (e.g., nasal cancer from inhaled vapors). In 1995, IARC classified formaldehyde as a probable human carcinogen (mainly nasopharyngeal). By 2004, it was upgraded to a "known carcinogen."

Confirmed links include nasal sinus cancer, nasopharyngeal cancer, lung cancer, pancreatic cancer, and myeloid leukemia. Long-term occupational exposure doubles mortality rates for these cancers compared to the general population.

SYMPTOMS

What are the common symptoms of formaldehyde poisoning?

• Irritation to mucous membranes and skin:

  • Commonly seen with formaldehyde vapor. Symptoms include burning pain in the eyes, increased tearing, redness and swelling of the eyes (including eyelid edema and conjunctival edema), keratitis (manifested as photophobia, tearing, and severe eye pain), rhinitis, loss of smell, pharyngitis, bronchitis, etc. In severe cases, laryngeal spasm (feeling of throat blockage and difficulty breathing) and laryngeal edema (hoarseness, shortness of breath, etc.) may occur.

  • Prolonged skin contact can cause dryness, cracking, abnormal roughness of the palms, localized redness, erythema, papules (raised bumps or small nodules), itching (including acute allergic reactions), etc. Severe cases may involve paronychia and nail softening. Commonly affects the hands, fingers, face, and forearms.

• Oral poisoning: Symptoms include burning pain in the mouth, throat, esophagus, and stomach, erosion of oral mucosa, severe abdominal pain, sometimes vomiting blood, diarrhea, or bloody stools. In more severe cases, gastrointestinal erosion or perforation may lead to shock, coma, metabolic acidosis, liver and kidney damage, or even death.

• Chronic low-level exposure (chronic poisoning): Symptoms may include dizziness, headaches, general fatigue, digestive disorders (loss of appetite, indigestion, bloating), excitement, tremors, and vision impairment. At formaldehyde concentrations of 20–70 mg/m³, symptoms such as loss of appetite, fatigue, headaches, palpitations, and insomnia may occur.

• Some literature suggests that formaldehyde may also cause disturbances in touch, pain, and temperature sensation, often localized to one side of the body (more commonly the right) or specific areas, excessive sweating on one side, and unequal skin temperature on both sides of the body.

What are the symptoms of mild formaldehyde poisoning?

• Obvious conjunctival congestion and edema (red, swollen eyes), irritation of the upper respiratory tract mucosa (such as nasal congestion, sneezing, runny nose, coughing, etc.);

• Grade 1–2 laryngeal edema (self-perceived hoarseness, slight or no difficulty breathing at rest, worsening symptoms with mild activity).

What are the symptoms of moderate formaldehyde poisoning?

• Persistent coughing, phlegm, chest tightness, difficulty breathing, etc.;

• Grade 2–3 laryngeal edema (feeling of throat swelling, difficulty breathing, accompanied by restlessness due to hypoxia, pale or bluish lips and fingers, palpitations, etc.);

• Blood gas analysis shows mild to moderate hypoxemia.

What are the symptoms of severe formaldehyde poisoning?

• Pulmonary edema;

• Grade 4 laryngeal edema (loss of consciousness, sudden drowsiness, pale or grayish complexion, etc.);

• Blood gas analysis shows severe hypoxemia.

Which parts of the body are commonly affected by formaldehyde poisoning?

• When exposed to gaseous formaldehyde, irritation and damage primarily occur in the mucous membranes of the eyes, nose, mouth, and respiratory tract.

• When exposed to liquid formaldehyde, symptoms mainly affect the skin, nails, limbs, and digestive tract (mouth, gastrointestinal tract).

What serious consequences can formaldehyde poisoning cause?

• Mild cases may involve skin and mucous membrane damage (localized redness, swelling, pain, itching, increased secretions);

• Moderate cases may lead to skin lesions, oral mucosal ulcers, and erosion (simply understood as mouth sores, gastrointestinal ulcers, or even perforation);

• Severe cases may result in death due to acute laryngeal edema, severe hypoxemia, or circulatory failure (severe liver and kidney damage).

CAUSES

What are the common causes of formaldehyde poisoning?

Commonly classified as acute or chronic poisoning:

• Acute poisoning is mostly caused by accidental ingestion or intentional poisoning.

• Chronic poisoning: Due to its wide range of applications, formaldehyde is often used as a raw material in industries for synthesizing resins, plastics, paper, rubber, leather tanning, paints, pharmaceuticals, and artificial fibers. It is also an important organic synthetic material in chemical, pharmaceutical, and textile industries. In agriculture, it is commonly used for fumigation to disinfect inoculation rooms, granaries, and silkworm rearing rooms, as well as for seed sterilization by soaking wheat, cotton, and rice in aqueous solutions. Workers in these fields may suffer from chronic exposure due to long-term contact.

Who is most susceptible to formaldehyde poisoning?

Since formaldehyde is widely used in medicine (e.g., specimen preservation in formalin), chemistry, industry, agriculture, and decoration for disinfection, preservation, and fumigation, poisoning is most common among people working in these fields.

DIAGNOSIS

How is formaldehyde poisoning diagnosed?

Doctors diagnose it based on clinical symptoms and blood test results. For example, if you have been exposed to a renovated or laboratory environment for a long time or ingested an unknown liquid, and experience symptoms like dizziness, eye pain, nausea, vomiting, allergies, or abdominal pain, toxicology analysis may detect formaldehyde in your body (which is not present in healthy individuals), leading to a confirmed diagnosis.

Therefore, if this condition is suspected, the following tests may be performed:

• Toxicology analysis: This test requires a blood sample, but fasting is not mandatory. A urine sample may also be collected. If ingestion is suspected, bringing the container of the ingested substance can aid in testing.

• Blood test: Fasting is required to assess whether formaldehyde has caused liver or kidney damage.

• Chest X-ray or CT scan: To evaluate lung damage.

• Gastroscopy: If formaldehyde was ingested, this procedure examines gastrointestinal mucosal damage. However, it is usually not performed during acute erosion phases and may be considered later based on the patient's condition.

What precautions should be taken for the above tests for formaldehyde poisoning?

First, it is crucial to note that formaldehyde detection requires specialized equipment, which most non-military hospitals lack! Therefore, patients should confirm in advance which qualified hospitals (usually military hospitals) can perform the tests.

• If poisoning is suspected, preserve any suspicious containers, vomit, or other evidence. Collect blood and urine samples immediately upon hospitalization (some hospitals may store them for you) and send them to a qualified facility for toxicology analysis. Repeat testing may be necessary during treatment to monitor toxin levels and adjust the treatment plan accordingly.

• Due to radiation exposure, frequent or unnecessary CT scans should be avoided. Pregnant women cannot undergo CT scans. CT scans include plain scans, contrast-enhanced scans (using intravenous organic iodine for clearer imaging), and angiographic scans (contrast agent injection before scanning). Patients allergic to iodine or contrast agents cannot undergo enhanced or angiographic scans.

• For gastrointestinal contrast imaging, fasting for 4–6 hours is typically required. Patients prone to hypoglycemia should carry candy or drinks to prevent low blood sugar. To avoid artifacts affecting image quality, remove metal objects from the scanned area—no hairpins or earrings for head scans, and no belts or corsets for abdominal scans.

TREATMENT

Which department should I visit for formaldehyde poisoning?

It is usually seen as acute poisoning damage, so you can first go to the emergency department.

• In primary-level hospitals, further triage is based on the severity of the damage. For example, severe respiratory damage may require admission to the respiratory department, severe gastrointestinal damage to the gastroenterology department, and severe systemic poisoning symptoms (such as coma) to the intensive care unit (ICU).

• In higher-level comprehensive hospitals with more specialized divisions, some emergency departments have professional qualifications for acute poisoning treatment, allowing direct hospitalization in the emergency department.

Can formaldehyde poisoning heal on its own?

Mild poisoning, such as temporary exposure causing tearing, eye pain, or itchy skin, can resolve on its own if the person quickly leaves the environment, with or without treatment. For moderate to severe cases, formal treatment at a hospital is recommended.

How is formaldehyde poisoning treated?

There is no specific antidote for formaldehyde, so treatment is generally symptomatic:

• Remove from the hazardous environment: Take the patient away from the area, remove contaminated clothing, and rinse the skin thoroughly with soapy water (alkaline solution) or clean water.

• Seek immediate medical attention. Hospitals may provide oxygen therapy, steroids, nebulization, or anti-infection treatments based on symptoms. After cautious gastric lavage, medication can be given to convert formaldehyde into less toxic urotropine. Drinking milk or soy milk can help protect the gastric mucosa.

Does formaldehyde poisoning require hospitalization?

For mild damage (e.g., brief, minor skin or eye exposure), proper handling (removing the source of exposure and cleaning the affected area) and long-term observation without discomfort may suffice, making hospitalization unnecessary.

For moderate to severe cases, hospital evaluation is recommended. Blood tests (to assess liver and kidney function and check for hypoxia due to respiratory damage) and chest X-rays or CT scans (to examine lung conditions) will determine whether hospitalization is needed.

Can formaldehyde poisoning be completely cured?

In poisoning cases, generalizations cannot be made without considering dosage and concentration.

Short-term, low-dose exposure without severe organ damage can be fully cured with proper treatment, adequate rest, and avoiding re-exposure.

Severe damage or long-term chronic poisoning increases the risk of organ failure or tumors.

DIET & LIFESTYLE

What should patients with formaldehyde poisoning pay attention to in their daily life and diet?

• In the early stages of poisoning, especially for orally poisoned patients, start with a liquid diet at a suitable temperature (some people prefer hot food, which can worsen the already damaged gastrointestinal and esophageal mucosa—this must be avoided). Avoid hard or sharp-edged foods like nuts and crackers, but do not make the diet overly monotonous (e.g., endless servings of noodle soup, which can lead to severe nutritional deficiencies and hinder the healing of damaged mucosa). Supplement with high-quality protein (such as moderate amounts of milk, soy milk, beef broth, etc.), balancing sweet and savory flavors.

• Since formaldehyde severely damages mucous membranes, patients with confirmed lung, tracheal, or bronchial injuries must stay warm and avoid colds. If visitors have severe colds, ask them to postpone their visit.

• Strictly avoid alcohol and smoking.

Do patients with formaldehyde poisoning need follow-up examinations?

Hospitalized poisoning patients should have a follow-up examination two weeks after discharge. Subsequent follow-ups should be scheduled based on their condition.

Does formaldehyde poisoning affect fertility?

Currently, there is no evidence that formaldehyde has reproductive toxicity, so it does not affect fertility. However, it is generally recommended to wait until full recovery and confirmation of no abnormalities in follow-up examinations before planning pregnancy.

Can patients with formaldehyde poisoning fly, engage in strenuous exercise, or travel to high-altitude areas?

There is no definitive research on this, but during the acute injury phase, mucous membranes, respiratory tracts, and digestive organs are in a state of damage and hypoxia. Conditions like low pressure, hypoxia, fatigue, or travel may worsen the condition, so flying, exercising, or traveling during this period is not recommended.

How should family members care for a patient with formaldehyde poisoning?

• Provide appropriate dietary choices based on different stages of the illness.

• Offer sufficient psychological support to alleviate anxiety, depression, and other negative emotions caused by pain and discomfort, encouraging the patient to actively cooperate with treatment and attend follow-up examinations on time.

• Take good care of the patient to avoid secondary infections due to weakened immunity, which could delay recovery and worsen the current condition.

PREVENTION

How to Prevent/Avoid Formaldehyde Poisoning?

• Containers storing formaldehyde solutions must be tightly sealed and inspected regularly, especially in high-temperature and high-humidity climates.

• Ensure proper air circulation in the working environment and maintain ventilation systems during work.

• Individuals with respiratory diseases, neurological disorders, skin conditions, or allergic predispositions should avoid exposure. Even healthy individuals who suddenly develop such symptoms should consciously avoid contact with formaldehyde.

• When renovating a new home, purchase materials that meet national standards. Keep the newly renovated house well-ventilated and avoid immediate occupancy.

• For textiles, soak and thoroughly wash newly purchased clothes before wearing, especially undergarments and infant clothing.

• For food, buy products from reputable manufacturers, prioritize fresh ingredients, and consciously avoid overly white steamed buns, rolls, vermicelli, cold-soaked products, or preserved foods like duck feet that require soaking.