1. Education
You can opt-out at any time. Please refer to our privacy policy for contact information.

Discuss in my forum

Chemical Composition of the Human Body

Elements in the Human Body


Here's a look at the chemical composition of the human body, including element abundance and how each element is used. Elements are listed in order of decreasing abundance, with the most common element (by mass) listed first. Approximately 96% of body weight consists of only four elements: oxygen, carbon, hydrogen, and nitrogen. Calcium, phosphorus, magnesium, sodium, potassium, chlorine, and sulfur are macronutrients or elements the body needs in a significant amount.

1. Oxygen

Liquid oxygen is blue.
Warwick Hillier, Australia National University, Canberra
By mass, oxygen is the most abundant element in the human body. If you think about it, this makes sense, since most of the body consists of water or H2O. Oxygen accounts for 61-65% of the mass of the human body. Even though there are many more atoms of hydrogen in your body than oxygen, each oxygen atom is 16 times more massive than a hydrogen atom.


Oxygen is used for cellular respiration.

2. Carbon

Photograph of graphite, one of the forms of elemental carbon.
U.S. Geological Survey
All living organisms contain carbon, which forms the basis for all of the organic molecules in the body. Carbon is the second most abundant element in the human body, accounting for 18% of body weight.


All organic molecules (fats, proteins, carbohydrates, nucleic acids) contain carbon. Carbon also is found as carbon dioxide or CO2. You inhale air that contains about 20% oxygen. Air you exhale contains much less oxygen, but is rich in carbon dioxide.

3. Hydrogen

This is a vial containing ultrapure hydrogen gas.
Wikipedia Creative Commons License
Hydrogen accounts for 10% of the mass of the human body.


Since around 60% of your body weight is water, much of the hydrogen exists in water, which functions to transport nutrients, remove wastes, lubricate organs and joints, and regulate body temperature. Hydrogen is also important in energy production and use. The H+ ion can be used as a hydrogen ion or proton pump to produce ATP and regulate numerous chemical reactions. All organic molecules contain hydrogen in addition to carbon.

4. Nitrogen

This is a photo of liquid nitrogen being poured from a dewar.
Cory Doctorow
Approximately 3% of the mass of the human body is nitrogen.


Proteins, nucleic acids, and other organic molecules contain nitrogen. Nitrogen gas is found in the lungs, since the primary gas in air is nitrogen.

5. Calcium

Calcium is a metal.
Tomihahndorf, Creative Commons License
Calcium accounts for 1.5% of human body weight.


Calcium is used to give the skeletal system its rigidity and strength. Calcium is found in bones and teeth. The Ca2+ ion is important for muscle function.

6. Phosphorus

White phosphorus powder glows green in the presence of oxygen.
Luc Viatour, Creative Commons License
About 1.2% to 1.5% of your body consists of phosphorus.


Phosphorus is important for bone structure and is part of the primary energy molecule in the body, ATP or adenosine triphosphate. Most of the phosphorus in the body is in the bones and teeth.

7. Potassium

These are chunks of potassium metal. Potassium is a soft, silvery-white metal that quickly oxidizes.
Dnn87, Creative Commons License
Potassium makes up 0.2% to 0.35% of the adult human body.


Potassium is an important mineral in all cells. It functions as an electrolyte and is particularly important for conducting electrical impulses and for muscle contraction.

8. Sulfur

This is a sample of pure sulfur, a yellow nonmetallic element.
Ben Mills
Sulfur's abundance is 0.20% to 0.25% in the human body.


Sulfur is an important component of amino acids and proteins. It's present in keratin, which forms skin, hair, and nails. It's also needed for cellular respiration, allowing cells to use oxygen.

9. Sodium

Sodium is a soft, silvery reactive metal.
Dnn87, Creative Commons License
Approximately 0.10% to 0.15% of your body mass is the element sodium.


Sodium is an important electrolyte in the body. It is an important component of cellular fluids and is needed for the transmission of nerve impulses. It helps regulate fluid volume, temperature, and blood pressure.

10. Magnesium

Crystals of elemental magnesium.
Warut Roonguthai
The metal magnesium comprises about 0.05% of human body weight.


About half of the body's magnesium is found in the bones. Magnesium is important for numerous biochemical reactions. It helps regulate heart beat, blood pressure, and blood glucose levels. It is used in protein synthesis and metabolism. It is needed to support proper immune system, muscle, and nerve function.

©2014 About.com. All rights reserved.