A total of five fatalities and over 67 hospital admissions have been reported after ammonia gas leaked from a seafood processing plant in Tiruvallur district in Tamil Nadu on Sunday (June 21, 2026). What is ammonia, and how does it affect the human body? Here is all you need to know about ammonia poisoning.

What is ammonia?

Ammonia is a clear, colourless gas with a pungent, rotting fish odour. It occurs naturally and through human activity. It is made up of one nitrogen atom and three hydrogen atoms, with the chemical formula NH₃. It can also be compressed into a liquid and can be dissolved in water. It is an important chemical, used in various agricultural and industrial processes such as in the manufacture of fertilisers, cleaning products, plastics, dyes, and in cooling systems.

How does ammonia poisoning occur?

Ammonia is highly toxic. Ammonia poisoning or toxicity can occur when ammonia is inhaled, ingested, or comes into direct contact with the skin or eyes. In the Tiruvallur case, ammonia was being used as a refrigerant, and the gas tank leaked, causing it to be inhaled by workers who were at the factory at the time.

In general, ammonia is rapidly converted into urea by the liver, and then excreted by the kidneys. Ammonia toxicity occurs when the amount of ammonia in the blood exceeds the liver’s capacity to eliminate it.

Ammonia, in its gas or liquid form, reacts with the water in human tissues to form ammonium hydroxide, a corrosive alkali that causes burning and tissue damage. The United States’ Agency for Toxic Substances and Disease Registry’s medical management guidelines for ammonia state that inhalation of ammonia may cause nasopharyngeal and tracheal burns, bronchiolar and alveolar edema (swelling), and airway destruction resulting in respiratory distress or failure. It adds that exposure to ammonia gas or ammonium hydroxide can result in corrosive injury to the mucous membranes of the eyes, lungs, and gastrointestinal tract, and to the skin due to the alkaline pH and the hygroscopic nature of ammonia.

At what concentration is it toxic?

According to a continuing education activity paper on ammonia toxicity by Rana Prathap Padappayil and Judith Borger, ammonia concentrations of up to 100 ppm in the air are tolerated well for up to several hours. At 1,700 ppm, the glottic region’s (larynx region) coughing, laryngospasm, and edema (swelling) start. Concentrations of 2,500 ppm to 4,500 ppm can be fatal in approximately 30 minutes, and concentrations above 5,000 ppm usually produce rapid respiratory arrest. Anhydrous ammonia in concentrations above 10,000 ppm is sufficient to cause skin damage. The concentration at which the gas is immediately harmful to life or health is 300 ppm, it says.

What are the signs and symptoms?

People who inhale ammonia may experience a scratchy throat, running nose, chest tightness, cough, shortness of breath or breathing difficulties, eye irritation, a burning feeling in the nose, throat, lungs, and eyes, and narrowing of the throat and swelling. Prolonged or severe exposure to the gas can result in skin burns. Exposure to very high levels can cause death.

The medical management guidelines note that the extent of injury depends on the duration of the exposure, the concentration of the gas, and the depth of inhalation. Even fairly low airborne concentrations (50 ppm) of ammonia produce rapid onset of eye, nose, and throat irritation; coughing; and narrowing of the bronchi, it says. More severe clinical signs include immediate narrowing of the throat and swelling, causing upper airway obstruction and accumulation of fluid in the lungs. When the oxygen levels in the blood become low, it can result in altered mental status. Mucosal burns to the airways can also occur, it adds.

What does treatment involve?

There is no known cure for ammonia poisoning. There is also no test to evaluate the extent of systemic toxicity. The goal of treatment is to remove the ammonia from the body as soon as possible and provide supportive treatment. This may include supporting breathing with the help of oxygen, treatment for burns, and treatment of the eyes in case there is irritation or injury.

Survivors of severe inhalation injury may suffer residual chronic lung disease, according the guidelines. In cases of eye contact, ulceration and perforation of the cornea can occur after weeks or months, and blindness may ensue. Cataracts and glaucoma have also been reported in persons acutely exposed, the guidelines state.