How many cell types are in the human body?
Why published counts run from 200 to thousands
Matic Broz, PhD10 min
The human body has about 400 major cell types by the most detailed modern counts, roughly twice the figure of 200 still given in many textbooks. Sort cells by which genes they use rather than by how they look and what they do, and the count climbs into the thousands: one atlas of the adult brain alone distinguished 3,313 molecular subclusters.
There is no final number because a cell type is a category that scientists define, not an object they can count. A red blood cell and a neuron are plainly different. Two T cells that use slightly different sets of genes may or may not be, depending on the method and the threshold. That question is separate from the number of cells in the body, about 30 to 37 trillion, most of which belong to a single type.
How many cell types are in the human body?
Published whole-body counts run from about 200 to about 475, and the spread reflects method more than disagreement about biology. The figure of about 200 is the long-standing textbook estimate, repeated in NIH educational material in 2024.[1] When Vickaryous and Hall compiled a list of adult human cell types from the literature in 2006, they recognized 411, of which 145 were kinds of neurons.[2]
Hatton and colleagues arrived at a similar total from a different direction in 2023. Their census of cell numbers and sizes drew on more than 1,500 sources and sorted the body into about 400 major cell types across 60 tissue systems.[3]
Single-cell atlases, which classify cells by the RNA they contain, land in the same range. The first Tabula Sapiens atlas profiled 483,152 cells from 24 tissues and organs of 15 donors and described 475 distinct cell types.[4] Its 2025 update reports a lower figure for unique types and a higher one for types counted organ by organ, a difference explained below.
| Source | Method and scope | What was counted | Count |
|---|---|---|---|
| Textbook figure (NIGMS, 2024) | Classical histology: appearance, location and function | Cell types | About 200 |
| Vickaryous and Hall (2006) | Literature review of structure, function and development | Adult cell types, 145 of them neurons | 411 |
| Hatton et al. (2023) | Census of cell numbers and sizes from over 1,500 sources | Major cell types | About 400 |
| Hatton et al. (2023) | Same census, finer classification | Specific cell types | 924 |
| Tabula Sapiens (2022) | Single-cell RNA sequencing, 24 tissues, 15 donors | Annotated cell types | 475 |
| Tabula Sapiens 2.0 (2025) | Single-cell RNA sequencing, 28 tissues, 24 donors | Cell types counted once | 175 |
| Tabula Sapiens 2.0 (2025) | Same data, each tissue counted separately | Cell type and tissue combinations | 701 |
| Siletti et al. (2023) | Single-nucleus RNA sequencing of the brain only | Clusters and subclusters | 461 and 3,313 |
About 400 is the most defensible whole-body answer at the level of major types, because two independent literature compilations, 17 years apart, land near it. The rest of the table shows how far the number moves once the counting rules change.
Why do cell-type counts range from 200 to thousands?
The first reason is the level of classification. Hatton and colleagues organized a single dataset at four levels: 18 broad cell classes, about 400 major types, 924 more specific types and 1,264 cell groups defined by tissue.[3]
These are not competing estimates. An immune cell is a broad class, a T cell is a major type, and a regulatory T cell is a finer type within it. Each level is correct for its own purpose, and the textbook 200 sits near the coarse end of the same scale.
The second reason is whether a cell type found in several organs is counted once or once per organ. Endothelial cells, which line blood vessels, and macrophages turn up in almost every tissue.[4] The 2025 update of Tabula Sapiens reports both figures for 1.1 million cells from 28 tissues: 701 cell populations, each a cell type combined with its tissue of origin, and 175 cell types when each is counted once.[5] Our count of the first release's public data on CELLxGENE suggests its 475 works the same way: the 483,152 cells carry 161 distinct Cell Ontology labels, but the 24 organ datasets add up to 452 labels when each organ is counted separately.[7]
The third and largest factor is molecular resolution. Siletti and colleagues sequenced RNA from more than 3 million nuclei taken from about 100 regions of three adult brains and found 461 clusters and 3,313 subclusters, with especially high diversity among neurons of the midbrain and hindbrain.[6] Vickaryous and Hall's 145 neuron types and these thousands of subclusters describe the same organ at very different grain.
The 3,313 figure is the number of groups at the resolution that study chose, not a final inventory of brain cell types. Whether each subcluster deserves the name cell type depends on what a cell type is taken to be.
What counts as a cell type?
A cell type is a group of cells with a shared, relatively stable identity, usually defined by a combination of structure, function, location, developmental origin and molecular profile.[8]
No single test decides whether two cells are different types. A neuron and a liver cell differ clearly in shape, function and gene expression. The boundary between two closely related immune cells may depend on which markers are measured and how much difference a study requires before it creates a new category.
A cell type also differs from a cell state. A T cell can become activated during an immune response without becoming a new type, and the cell cycle, inflammation, aging and disease can all shift gene expression for a while. Because single-cell sequencing captures a snapshot, researchers must decide whether a cluster reflects a durable identity or a passing state.[8]
How do scientists identify human cell types?
Scientists identify cell types by combining microscopy, anatomy, function, developmental history and molecular measurements such as single-cell RNA sequencing.[9] Classical histology relies on what cells look like, where they sit and what they do. Single-cell atlases measure which genes are active in each cell, group cells with similar profiles, and then match those groups to known anatomy and function.
Nearly every cell carries the same set of human genes; cell types differ in which of those genes they switch on and when.[9] Models such as AlphaGenome, which predicts how DNA sequence shapes gene regulation across tissues and cell types, work on exactly this difference.
The molecular approach still finds cells that microscopy missed. In 2018, single-cell profiling of the airway lining identified the pulmonary ionocyte, a rare cell that turned out to be a major source of activity of CFTR, the ion channel that is defective in cystic fibrosis.[10] The Human Cell Atlas, an international consortium, aims to map every human cell type in this way across tissues, life stages and populations.[9]
Which cell types are the most numerous?
Red blood cells are by far the most common cell type. A 70-kilogram reference man has about 25 trillion red blood cells, 84% of all his human cells.[11] Among the roughly 7 trillion cells that have a nucleus, white blood cells lead. Hatton and colleagues put them at about 3.4 trillion, almost all resident in tissues rather than circulating in blood, while a separate 2023 census of immune cells arrived at 1.8 trillion.[3][12]
| Measure | Leading cell type | Estimate |
|---|---|---|
| Number of cells | Red blood cells | 25 trillion, 84% of human cells |
| Number of nucleated cells | White blood cells | 1.8 to 3.4 trillion of about 7 trillion |
| Cell mass | Skeletal muscle fibers | About half of 45 kg of cells |
| Second-largest cell mass | White fat cells | About 12 kg |
Weigh the body instead of counting it, and the order reverses. Skeletal muscle fibers make up about half of the body's 45 kilograms of cells but less than 0.002% of its nucleated cells, and white fat cells add about 12 kilograms more.[3] Together, fat and muscle cells are only about 0.2% of the cell count.[11] Of some 400 major types, a few supply most of the body's cells and a few others most of its weight.
What cell types are found in each tissue?
Every organ combines a few cell types found almost everywhere, such as endothelial cells, fibroblasts and macrophages, with specialists found nowhere else.[4] Table 3 lists examples of the specialists from single-cell atlases. Many of these names cover several subtypes, and in the brain the word neuron covers far more variety than any single row can show.[6]
| Tissue | Example cell types |
|---|---|
| Blood | Red blood cells, platelets, neutrophils, monocytes, B cells, T cells, natural killer cells |
| Brain | Neurons, astrocytes, oligodendrocytes, oligodendrocyte precursor cells, microglia |
| Lung | Alveolar type 1 and type 2 cells, club cells, ciliated cells, goblet cells, ionocytes |
| Liver | Hepatocytes, cholangiocytes, hepatic stellate cells, macrophages |
| Small intestine | Enterocytes, goblet cells, Paneth cells, tuft cells, enteroendocrine cells, crypt stem cells |
| Pancreas | Acinar cells, ductal cells, and the alpha, beta, delta and PP cells of the islets |
| Eye | Photoreceptors, retinal ganglion cells, Müller glia, retinal pigment epithelial cells |
| Skeletal muscle | Fast and slow muscle fibers, satellite stem cells |
| Skin | Keratinocytes, melanocytes, Langerhans cells, sebocytes |
Read together, the counts form a ladder rather than a contradiction. About 200 types describe the body as a histology textbook draws it, about 400 as a careful census of structure and function does, several hundred more when the same type is counted in each organ, and thousands when gene activity is the yardstick. Any total is only meaningful with its classification level beside it.
