Cremation is a process that transforms a human body into bone fragments and ashes through intense heat. When a body is cremated, it undergoes a series of physical and chemical changes driven primarily by high temperatures, typically around 1400 to 1800 degrees Fahrenheit (760 to 982 degrees Celsius), inside a specialized furnace called a cremation chamber or retort[2][5].
Initially, the body is placed inside the cremation chamber, often within a combustible container such as a wooden casket. The casket quickly ignites and burns away within the first few minutes, exposing the body directly to the heat and flames generated inside the chamber[2]. Modern cremators may use gas or electric heating elements rather than open flames, but the effect is the same: the body is subjected to extreme heat.
The intense heat causes the body’s soft tissues—skin, muscles, organs, and fat—to combust and vaporize. Water content in the body evaporates rapidly, and organic compounds break down into gases such as carbon dioxide, water vapor, and trace gases. This process effectively destroys all living cells, bacteria, viruses, and pathogens, ensuring that no infectious agents survive the cremation[2]. This is why cremation has historically been used to prevent the spread of disease during epidemics.
As the soft tissues are consumed, the body’s skeletal structure remains. Bones are primarily composed of calcium phosphate, a mineral that is much more heat-resistant than soft tissue. However, after about two hours in the cremation chamber, the bones undergo thermal decomposition. The heat causes the bones to become brittle and calcined, breaking down their molecular structure and turning them into a porous, white or grayish residue commonly called “cremated remains” or ashes[2]. These bone fragments are then processed in a machine called a cremulator, which pulverizes them into a fine powder.
The entire cremation process typically lasts between one and three hours, depending on factors such as the size of the body, the temperature of the chamber, and the type of container used[2][5]. After cremation, the remains consist mainly of bone fragments and trace amounts of metal from dental work or implants, which are usually removed before the ashes are returned to the family.
From a chemical perspective, cremation breaks down the complex organic molecules in the body into simpler compounds. The intense heat disrupts molecular bonds, converting proteins, fats, and carbohydrates into gases and mineral residues. This transformation ensures that the body is reduced to inorganic bone mineral and gaseous byproducts, with no recognizable biological material remaining[2].
In contrast to flame cremation, there is an alternative method called alkaline hydrolysis or water cremation. This process uses a heated solution of water and potassium hydroxide under pressure to chemically break down the body over several hours at lower temperatures (around 160 degrees Celsius or 320 degrees Fahrenheit). The body is dissolved into a sterile liquid containing amino acids, peptides, sugars, and salts, leaving behind only soft, porous bone fragments that can be crushed into ashes. This method is considered more environmentally friendly and is legal in several U.S. states[1][4].
Throughout cremation, the destruction of pathogens and organic material is complete, making the process safe and sanitary. The high temperatures and chemical reactions ensure that no viable bacteria, viruses, or DNA remain in the ashes, which are chemically very different from the original body[2].
In summary, during cremation, the body is exposed to extreme heat that vaporizes soft tissues, destroys pathogens, and calcines bones into ash. The process is both a physical and chemical transformation that reduces the body to inorganic mineral fragments and gases, leaving no biological hazard behind.
Sources:
[1] Wikipedia – Water cremation
[2] Cremationurns.net – Cremation and Contagion
[4] US-Funerals.com – Where is Aquamation Legal?
[5] YouTube – What Happens to a Body During Cremation? The Detailed Scientific Explanation
