What is a stem cell?

Stem Cell

A stem cell has the unique ability to develop into other specialised cell types in the body.

  • Stem cells are special cells that can turn into different types of cells.
  • In a developing embryo, they can develop into any type of cell. Once the body is grown, they can develop into specific cell types, to replace old or damaged cells.
  • In medicine, stem cells may be used to replace cells and tissues that have been damaged or lost due to disease.


What is a stem cell?


  • Our body is made up of many different types of cells.
  • Most cells are ‘specialised’, meaning they perform different functions. For example, red blood cells are specialised to carry oxygen around the body in the blood, while some gut cells are specialised to absorb nutrients from food.
  • All specialised cells start out as stem cells – the foundation for every organ and tissue in the body. They provide new cells for the body as it grows and replace specialised cells as they get older or damaged.
  • Stem cells are defined by two unique properties:
    • They can divide over and over again to produce new stem cells.
    • As they divide, they can change into the other types of cell that make up the body.


An illustration showing a stem cell giving rise to more stem cells or specialised cells. Image credit: Laura Olivares Boldú / Wellcome Connecting Science

There are three main types of stem cell:

Embryonic stem cells, which supply new cells for an embryo as it grows and develops into a baby

Embryonic stem cells are ‘pluripotent’, which means they can change into any cell in the body.

Adult stem cells, which replace old or damaged cells as an organism grows

Adult stem cells are ‘multipotent’, which means they can only change into some cells in the body – not all cell types. This is because they have already started to specialise, so can only develop further into a specific type of cell.

For example, blood (or ‘haematopoietic’) stem cells can only replace the various types of cells in the blood. Skin (or ‘epidermal’) stem cells can replace the different types of cells that make up our skin and hair.

Induced pluripotent stem cells (or ‘iPS cells’) are made in the laboratory

Normal adult cells (often skin cells) can be reprogrammed in the lab to become stem cells. This is called ‘inducing’ the stem cells.

Just like embryonic stem cells, they are pluripotent so can, theoretically, develop into any cell type.

An illustration showing different types of stem cell in the body. Image credit: Laura Olivares Boldú / Wellcome Connecting Science

Stem cells are used in research to understand basic biology and have the potential to treat different conditions in medicine. Find out more here.