Humans are primarily made of a few key elements, with oxygen, carbon, hydrogen, and nitrogen together accounting for more than 99% of the atoms in the human body. Oxygen is the most abundant element by mass, making up about 52% to 65% of the body, mainly because of the high water content. Carbon, the fundamental building block of life, comprises about 14% to 18.5%. Hydrogen makes up around 8% to 10%, and nitrogen about 2.4% to 3%. Other essential elements include calcium, phosphorus, sulfur, potassium, sodium, chlorine, magnesium, iron, and trace elements totaling a small fraction of the body's mass. The human body composition also includes water (about 60%-70%), proteins, fats (lipids), carbohydrates, DNA, RNA, and minerals, which together form cells, tissues, and organs. The elements form molecules such as proteins, fats, nucleic acids, and carbohydrates essential for life functions.