What Are Stem Cells? Types, Sources, Risks, and Therapy Costs

Few things in medicine spark as much hope and confusion as “stem cells” — but the University of Washington ISCRM warns that many clinic-advertised treatments are not stem cell therapies at all. This guide walks through the proven science, real risks, and costs to help you distinguish established treatments from marketing claims.

Number of cell types stem cells can become: over 200 ·
Annual stem cell transplants worldwide: over 80,000 ·
Years of clinical stem cell research: over 60 ·
Percentage of body cells that are stem cells: less than 1%

Three key facts, one pattern: the distance between what stem cells can do in the lab and what is currently approved for patients remains wide.

What are stem cells and what do they do?

Key properties of stem cells

• Stem cells are undifferentiated cells that can self-renew and differentiate into specialized cell types (Danaher Life Sciences)
• Two hallmark abilities: unlimited self-renewal and differentiation into multiple lineages
• They can develop into muscle, brain, blood, bone, and over 200 other cell types (Danaher Life Sciences)

How stem cells function as repair cells

• Stem cells serve as the body’s internal repair system, replacing damaged or dead cells across tissues (University of Washington ISCRM)
• In bone marrow, hematopoietic stem cells produce all blood and immune cells throughout life
• In skin and gut, stem cells continuously regenerate lining cells that are lost daily

The implication: every organ that repairs itself relies on resident stem cells. When that system fails — due to disease, aging, or injury — the body cannot fix itself without outside help.

Where do stem cells come from?

Embryonic stem cells

• Human embryonic stem cells (hESCs) are harvested from the inner cell mass of a blastocyst, a 5–7 day old embryo (Danaher Life Sciences)
• These cells are pluripotent — they can form all three germ layers and any cell type in the body
• The NIH-hosted review identifies four major obstacles: differentiation control, potential cancer formation, immune rejection, and ethical concerns over embryo harvesting (PMC / NIH)

Adult stem cells (bone marrow, fat, blood)

• Adult stem cells are resident progenitor cells found in organs, tissues, or circulating in blood (Danaher Life Sciences)
• Hematopoietic stem cells (HSCs) are traditionally isolated from bone marrow aspirate
• Mesenchymal stem cells (MSCs) can be isolated from bone marrow, umbilical cord blood, adipose tissue, peripheral blood, and other tissues (Danaher Life Sciences)

Induced pluripotent stem cells (iPSCs)

• iPSCs are adult somatic cells reprogrammed in the lab to behave like embryonic stem cells (Danaher Life Sciences)
• Discovered by Shinya Yamanaka in 2006, earning a Nobel Prize
• iPSCs avoid the ethical issues of embryo destruction but still carry cancer risk and genetic instability

The trade-off: embryonic cells offer the greatest potency but come with ethical and immune-rejection hurdles. Adult cells are safer and ethically straightforward but limited in what they can become. iPSCs bridge the gap but introduce new technical risks.

What are the types of stem cells?

Totipotent, pluripotent, multipotent stem cells

• Totipotent: can form any cell type including placenta and extraembryonic tissue — only the fertilized egg and its first few divisions are totipotent (Danaher Life Sciences)
• Pluripotent: can form all three germ layers (ectoderm, mesoderm, endoderm) but not placenta — includes hESCs and iPSCs
• Multipotent: limited to specific tissue types — HSCs produce blood cells, MSCs produce bone, cartilage, and fat cells

Three potencies, one pattern: each step down the hierarchy trades breadth for safety. The broader the potential, the harder it is to control where the cell goes and what it does.

Adult vs. embryonic vs. induced pluripotent

These three categories differ in source, potency, and clinical readiness.

What this means: embryonic cells have the most potential but also the most obstacles. Adult cells are already saving lives in the form of bone marrow transplants. iPSCs are the most exciting research tool, but no iPSC therapy has yet received FDA approval.

What are the risks of using stem cells?

Infection and immune rejection risks

• Stem cell transplants carry infection risk, especially after chemotherapy conditioning (University of Washington ISCRM)
• Graft-versus-host disease can occur when donor immune cells attack the recipient’s body
• The NIH review states that immune rejection of donor cells by the host immune system after transplantation is a primary concern (PMC / NIH)

Tumor formation risk

• Pluripotent stem cells have the potential to form teratomas — tumors containing multiple tissue types — if undifferentiated cells remain after transplantation (PMC / NIH)
• The same self-renewal ability that makes stem cells powerful also makes them prone to uncontrolled growth
• Differentiation control — ensuring all cells become the intended type before injection — remains a major technical hurdle

Unregulated stem cell clinics

• Many clinic-advertised stem cell interventions do not use stem cells at all, but rather tissue injections marketed as stem cell therapy (University of Washington ISCRM)
• The same source states there is no proof that any stem cell therapy offered by these clinics is effective or safe (University of Washington ISCRM)
• The FDA has warned about unapproved stem cell treatments that may cause blindness, infections, or tumors

Why this matters: the gap between legitimate stem cell medicine and the unregulated clinic industry is growing. Patients who seek hope for chronic conditions without understanding the difference face real medical harm.

Can stem cells reverse aging or turn cancerous?

The science of stem cells and aging

• Stem cell activity declines with age — older stem cells are less efficient at repairing tissue (Danaher Life Sciences)
• Aging research shows stem cell decline, not reversal — no treatment has proven to reverse human aging using stem cells
• Some studies suggest that reactivating aged stem cells could improve tissue repair, but this remains experimental

Stem cell mutation and cancer risk

• Stem cells divide throughout life, and each division carries a risk of mutation accumulation (PMC / NIH)
• Some therapies may promote cancer if the stem cells are not fully differentiated or if genetic instability is introduced during reprogramming
• The NIH review lists cancer formation as one of the four major obstacles to therapeutic use of embryonic stem cells (PMC / NIH)

The pattern: stem cells are not inherently dangerous, but their defining trait — the ability to divide indefinitely — is the same trait that defines cancer. Controlling that power is the central challenge of the field.

The pattern: stem cell research has delivered one approved therapy in over 60 years, while unproven clinics exploit patient hope.

Expert perspectives on stem cell therapy

Stem cells are defined by two key properties: the ability to self-renew and the ability to differentiate into specialized cell types. These properties make them a promising tool for regenerative medicine.

— Danaher Life Sciences, classification overview

Only a few FDA-approved stem cell-based therapies are available. Many of the treatments advertised by stem cell clinics are not stem cell therapies at all.

— University of Washington Institute for Stem Cell and Regenerative Medicine

Immune rejection of donor cells by the host immune system after transplantation is a primary concern, and differentiation control — ensuring cells become the intended type — remains a major hurdle.

— NIH-hosted review, PMC

Stem cell research has been underway for over 60 years, yet only one category — blood-forming stem cell transplants — has achieved broad FDA approval. The gap between laboratory promise and clinical reality is the single most important fact for anyone considering stem cell therapy today. For patients evaluating treatment options, the implication is clear: seek only therapies with FDA oversight or enrollment in a registered clinical trial, or risk spending thousands on unproven injections that may cause harm.