This is the elemental chemical composition of the average adult human body. Water is the most abundant chemical compound in living human cells, accounting for 65-90% of each cell. Each water molecule consists of two hydrogen atoms bonded to one oxygen atom, but the mass of each oxygen atom is much higher than the combined mass of the hydrogen. All organic compounds contain carbon, which is why carbon is the second most abundant element in the body. Six elements account for 99% of the mass of the human body: oxygen, carbon, hydrogen, nitrogen, calcium, and phosphorus. Although aluminum and silicon are abundant in the earth's crust, they are found in trace amounts in the human body.
Reference: Chang, Raymond (2007). Chemistry, Ninth Edition. McGraw-Hill. pp. 52.
Elements in the Human Body
| Element | Percent by Mass |
| Oxygen | 65 |
| Carbon | 18 |
| Hydrogen | 10 |
| Nitrogen | 3 |
| Calcium | 1.5 |
| Phosphorus | 1.2 |
| Potassium | 0.2 |
| Sulfur | 0.2 |
| Chlorine | 0.2 |
| Sodium | 0.1 |
| Magnesium | 0.05 |
| Iron, Cobalt, Copper, Zinc, Iodine | <0.05 each |
| Selenium, Fluorine | <0.01 each |
