When human hair comes into contact with a flame, the resulting combustion is a rapid chemical event that produces a distinct smoke. Understanding what happens when hair burns involves looking at the specific elements that make up the hair shaft and how those elements react when exposed to high heat. The nature of the smoke and its inhalation consequences are directly linked to the fiber’s unique composition as a biological product.
The Chemical Composition of Hair
Human hair is a biological fiber composed of approximately 90% keratin, a structural protein. Keratin is a long-chain polymer built from various amino acids, which are the fundamental building blocks of protein. The elemental composition of hair consists of roughly 45% carbon, 28% oxygen, 15% nitrogen, 7% hydrogen, and about 5% sulfur.
The presence of sulfur is particularly significant, as it is integrated into the amino acid cysteine, a component of keratin. When two cysteine molecules bond together, they form cystine, creating disulfide cross-links that provide hair with its notable strength and characteristic shape. The high percentage of nitrogen and sulfur distinguishes its combustion from plant-based materials, and the breakdown of these compounds dictates the nature of the resulting smoke and odor produced.
Immediate Sensory Experience of Burning Hair
When hair is exposed to an open flame, the heat causes the keratin protein structure to rapidly break down through a process called pyrolysis. The hair fiber does not melt; instead, it tends to curl, shrivel, and combust quickly, often self-extinguishing if the heat source is removed promptly. The residual material is typically a brittle, dark, and irregularly shaped bead of carbonized material, not a sticky liquid.
The most noticeable immediate consequence is the production of a strong, highly unpleasant odor. This characteristic smell is a direct result of the breakdown of the sulfur-rich amino acids, specifically the cystine disulfide bonds. The release of sulfur-containing gases creates the distinctive sulfurous scent, which many people describe as similar to burning meat or rotten eggs. The smoke itself is generally thin, white, or gray, carrying fine particulate matter and various gaseous byproducts of the incomplete combustion.
Health Implications of Smoke Inhalation
Inhaling the smoke from burning hair introduces a variety of chemical compounds and fine particles into the respiratory system. The incomplete combustion of carbon, hydrogen, and oxygen produces carbon monoxide (CO), a colorless and odorless gas that interferes with the blood’s ability to transport oxygen. The nitrogen content leads to the creation of nitrogen oxides, and the sulfur content generates sulfur dioxide (\(SO_2\)) and hydrogen sulfide (\(H_2S\)).
Sulfur dioxide and hydrogen sulfide are potent irritants to the eyes, nose, and respiratory tract. Exposure can immediately trigger coughing, a sore throat, and a burning sensation in the chest. These gases dissolve on the moist surfaces of the airways and lungs, creating acids that can damage the delicate lining of the respiratory passages.
The smoke also contains ultrafine particulate matter, which are microscopic solid particles that can penetrate deep into the lungs. These particles can cause inflammation and irritation, potentially exacerbating pre-existing conditions like asthma or chronic bronchitis. Systemic toxicity is a concern, particularly with larger volumes of smoke, due to the presence of carbon monoxide. This gas binds to hemoglobin in the blood, reducing the oxygen supply to organs and tissues, which can lead to symptoms such as headache, dizziness, and confusion.
Managing Accidental Hair Burns and Smoke Exposure
If hair catches fire, the immediate priority is to extinguish the flames and cool any resulting burn injury. The fire must be smothered using water or a non-flammable material, and the affected person should stop any movement immediately. Any burned area of the scalp or skin needs to be cooled with cool, running water for a minimum of 10 minutes to reduce tissue damage.
Following any smoke exposure, the person should move immediately to an area with fresh, clean air. Even if the exposure was brief, it is prudent to monitor for symptoms of respiratory irritation, such as a persistent cough, hoarseness, or difficulty breathing. If a person experiences any of these symptoms, or if the burn is large, deep, or on the face, they should seek professional medical attention immediately. Medical professionals can assess for internal damage from smoke inhalation, as inhalation injuries can sometimes have delayed symptoms.