---
title: "Hair Follicle | Anatomy and Physiology I"
description: "Hair follicle is the skin tube that surrounds the hair root and drives growth cycles in Anatomy and Physiology I, from anagen to shedding and regrowth."
canonical: "https://fiveable.me/anatomy-physiology/key-terms/hair-follicle"
type: "key-term"
subject: "Anatomy and Physiology I"
unit: "Unit 5"
---

# Hair Follicle | Anatomy and Physiology I

## Definition

A hair follicle is the tubular skin structure that surrounds the hair root and produces hair. In Anatomy and Physiology I, it is the accessory structure that supports hair growth and the hair cycle.

## What It Is

A hair follicle is the tubular pocket in the skin that surrounds the root of a hair and makes hair growth possible in Anatomy and Physiology I. It is not just a hole for the hair to sit in. It is living tissue, built from layers of skin that fold inward and create a protected space where new hair can form.

At the base of the follicle is the hair bulb, where actively dividing cells generate the hair shaft. Those cells sit near the dermal papilla, a small mound of connective tissue that brings in blood vessels and signals needed for growth. That blood supply is part of why the follicle can keep producing hair instead of just holding an old strand in place.

The follicle changes shape and activity across the hair growth cycle. During anagen, the growth phase, matrix cells divide quickly and the hair lengthens. In catagen, growth slows and the follicle shrinks. In telogen, the resting phase, the old hair is retained for a while before it is shed and a new cycle begins. This is why hair is constantly renewing rather than growing all at once.

Follicles are found over most of the body, but not on the palms of the hands or soles of the feet. That detail matters because those areas are specialized for thick skin, friction, and grip, not hair production. On a skin diagram, the follicle is usually shown below the epidermis, extending into the dermis and sometimes the upper hypodermis.

The follicle also connects to other skin structures. Sebaceous glands usually empty sebum into the follicle, and the arrector pili muscle attaches to it and can make hair stand up. So when you see a follicle, think of a tiny growth unit, not just the visible hair itself. The hair shaft is what you see above the skin, but the follicle is the part doing the work below it.

## Why It Matters

Hair follicles show up any time Anatomy and Physiology I moves from basic skin layers to the accessory structures of the skin. If you can picture the follicle, you can explain where hair comes from, why hair grows in cycles, and how skin conditions affect hair production.

It also gives you a clean way to connect structure to function. The follicle is a good example of how the body uses specialized tissue, blood supply, and stem cell activity to make a structure that keeps renewing itself. That idea comes up again in other organs and body systems, so follicles are a useful model for thinking about growth and repair.

This term also helps with common clinical examples. Hair loss can be traced to problems in the follicle, while folliculitis involves inflammation around the follicle. When a question asks why a hair is falling out, growing oddly, or becoming infected, the follicle is often the structure to inspect first.

## Connections

### [Sebaceous Gland](/anatomy-physiology/key-terms/sebaceous-gland)

Sebaceous glands usually open into the hair follicle and add sebum, an oily secretion that helps lubricate the hair and skin. When you study a follicle diagram, the gland is often shown attached to the upper part of the follicle. That connection matters because oil production and hair growth happen side by side.

### Arrector Pili Muscle

The arrector pili muscle attaches to the hair follicle and contracts when you get cold or startled. That contraction pulls the follicle upright and causes goosebumps. It does not make hair grow, but it shows how the follicle is linked to skin movement and surface changes.

### [Dermal Papilla](/anatomy-physiology/key-terms/dermal-papilla)

The dermal papilla sits at the base of the follicle and supplies signals and nutrients that support hair growth. It works with the growth cells in the bulb, so it is part of the control center for the follicle. If the papilla is damaged or weak, hair production can be affected.

### [anagen](/anatomy-physiology/key-terms/anagen)

Anagen is the active growth phase of the hair cycle, when follicle cells divide and the hair shaft gets longer. This is the phase most people mean when they talk about hair actively growing. The follicle has to stay healthy and well supplied during anagen for normal hair length and replacement.

## On the AP Exam

A quiz question might show a skin diagram and ask you to identify the hair follicle, the root, or the bulb, so you need to know which part is below the epidermis and which part is visible above it. If a short answer asks how hair grows, trace the follicle through anagen, catagen, and telogen instead of just saying it is a place where hair is found. In lab images, the follicle is the tubular structure surrounding the root, often paired with the sebaceous gland and arrector pili muscle. If a case mentions hair loss or follicle inflammation, connect the symptom to the follicle itself, not just the hair shaft.

## Key Takeaways

- A hair follicle is the living tubular structure in the skin that surrounds the hair root and produces hair.
- The follicle is where hair growth starts, especially in the anagen phase when cells in the bulb divide quickly.
- The dermal papilla supports the follicle with blood supply and signals that help hair form and renew.
- Hair follicles are found over most of the body, but not on the palms or soles.
- Follicles connect to other skin structures like sebaceous glands and arrector pili muscles.

## FAQs

### What is a hair follicle in Anatomy and Physiology I?

A hair follicle is the tubular skin structure that surrounds the root of a hair and produces the hair shaft. In Anatomy and Physiology I, it is studied as an accessory structure of the skin that supports hair growth and renewal.

### What is the difference between a hair follicle and a hair shaft?

The follicle is the living structure inside the skin that makes and holds the hair, while the hair shaft is the part you can see above the skin. A lot of students mix them up because only the shaft is visible, but the follicle is the growth site.

### Where are hair follicles found in the body?

Hair follicles are found throughout most of the skin, but not on the palms of the hands or the soles of the feet. That pattern fits the function of those areas, which are specialized for friction and thickness rather than hair growth.

### How does a hair follicle grow hair?

The follicle grows hair by using dividing cells in the bulb to build the hair shaft. During anagen, those cells are highly active, while catagen and telogen slow or pause the process before a new cycle starts.

## Related Study Guides

- [5.2 Accessory Structures of the Skin ](/anatomy-physiology/unit-5/2-accessory-structures-skin/study-guide/nr9xrmrHZhGOqQyN)

## About This Document

Canonical Fiveable pages are available as Markdown at the same path plus `.md`.

- [llms.txt](https://fiveable.me/llms.txt): index of Fiveable's sections and URL patterns
- [llms-full.txt](https://fiveable.me/llms-full.txt): complete subject and unit listing
- [MCP server](https://fiveable.me/mcp): call Fiveable as tools instead of fetching pages (`https://fiveable.me/api/mcp`)
- [MCP server for AP teachers](https://fiveable.me/mcp/teachers): a teacher's classes, assignments and AP-rubric grading (`https://fiveable.me/api/mcp/teacher`)

## Structured Data

```json
{"@context":"https://schema.org","@graph":[{"@type":"LearningResource","@id":"https://fiveable.me/anatomy-physiology/key-terms/hair-follicle#resource","name":"Hair Follicle | Anatomy and Physiology I","url":"https://fiveable.me/anatomy-physiology/key-terms/hair-follicle","learningResourceType":"Concept explainer","educationalLevel":"AP® / High School","about":{"@id":"https://fiveable.me/anatomy-physiology/key-terms/hair-follicle#term"},"audience":{"@type":"EducationalAudience","educationalRole":"student"},"dateModified":"2026-07-03T02:20:39.382Z","isPartOf":{"@type":"Collection","name":"Anatomy and Physiology I Key Terms","url":"https://fiveable.me/anatomy-physiology/key-terms"},"publisher":{"@type":"Organization","name":"Fiveable","url":"https://fiveable.me"}},{"@type":"DefinedTerm","@id":"https://fiveable.me/anatomy-physiology/key-terms/hair-follicle#term","name":"hair follicle","description":"A hair follicle is the tubular skin structure that surrounds the hair root and produces hair. In Anatomy and Physiology I, it is the accessory structure that supports hair growth and the hair cycle.","url":"https://fiveable.me/anatomy-physiology/key-terms/hair-follicle","inDefinedTermSet":{"@type":"DefinedTermSet","name":"Anatomy and Physiology I Key Terms","url":"https://fiveable.me/anatomy-physiology/key-terms"}},{"@type":"FAQPage","mainEntity":[{"@type":"Question","name":"What is a hair follicle in Anatomy and Physiology I?","acceptedAnswer":{"@type":"Answer","text":"A hair follicle is the tubular skin structure that surrounds the root of a hair and produces the hair shaft. In Anatomy and Physiology I, it is studied as an accessory structure of the skin that supports hair growth and renewal."}},{"@type":"Question","name":"What is the difference between a hair follicle and a hair shaft?","acceptedAnswer":{"@type":"Answer","text":"The follicle is the living structure inside the skin that makes and holds the hair, while the hair shaft is the part you can see above the skin. A lot of students mix them up because only the shaft is visible, but the follicle is the growth site."}},{"@type":"Question","name":"Where are hair follicles found in the body?","acceptedAnswer":{"@type":"Answer","text":"Hair follicles are found throughout most of the skin, but not on the palms of the hands or the soles of the feet. That pattern fits the function of those areas, which are specialized for friction and thickness rather than hair growth."}},{"@type":"Question","name":"How does a hair follicle grow hair?","acceptedAnswer":{"@type":"Answer","text":"The follicle grows hair by using dividing cells in the bulb to build the hair shaft. During anagen, those cells are highly active, while catagen and telogen slow or pause the process before a new cycle starts."}}]},{"@type":"BreadcrumbList","itemListElement":[{"@type":"ListItem","position":1,"name":"Anatomy and Physiology I","item":"https://fiveable.me/anatomy-physiology"},{"@type":"ListItem","position":2,"name":"Key Terms","item":"https://fiveable.me/anatomy-physiology/key-terms"},{"@type":"ListItem","position":3,"name":"Unit 5","item":"https://fiveable.me/anatomy-physiology/unit-5"},{"@type":"ListItem","position":4,"name":"hair follicle"}]}]}
```