Hair Follicle: Structure, Growth, Function & Conditions
The hair follicle – recognizing the importance of this tiny thing is key to understanding hair growth and loss.
Research states that we have, on average, over 5 million hair follicles across our entire body, with 100,000 on our scalp alone. They are an essential part of both growing hair and protecting it, as they influence the type and texture of our hair and maintain it throughout its growth phases.
But sadly, whether through injury, medical conditions, or genetics, our hair follicles can be disrupted from working correctly. And this can lead to all sorts of hair health problems and loss.
Today, we’ll explore everything you need to know about the human hair follicle. We’ll touch upon its functions, potential conditions, growth cycle, and ways to stimulate them back into action!
What is a hair follicle?
Hair begins its journey at the follicle, a long shaft found in the outer layer of our skin. It is microscopic and is the site where hairs sprout from. The hair follicle’s base has a blood vessel supply, which nourishes and supports the growing hair. Over time, the strand slowly rises to the surface of the hair shaft and protrudes from the skin.
The base of the follicle has a supply of blood vessels, which nourish and support the growing hair. Over time, and as the hair follicle is created, the strand slowly rises to the surface of the hair shaft.
Located inside the hair follicle are the sebaceous glands. These produce the natural oil, sebum, which keeps hair and skin moisturized and lubricated. Together with fat molecules, sebaceous glands also form a coating on the hair that protects it from germs and debris.
Hair follicle structure
Despite its small size, the hair follicle consists of many different parts, each crucial to ensuring hair grows strong and secure. Hair follicle morphogenesis (development) relies on four essential features:
- Dermal Papilla
The dermal papilla is located at the bottom of hair follicles and comprises of blood vessels, connective tissue, and mesenchymal cells (stem cells). Together, they nourish strands and ensure a blood supply to the hair follicle.
- Germinal Matrix
The germinal matrix surrounds the dermal papilla and is the site for new hair growth when old hair dies and falls out. The germinal matrix is also where melanin is transported to the hair, giving it its pigmentation or hair color.
- Hair Bulb
The hair bulb is a rounded structure found at the bottom of the hair follicle, surrounding both the dermal papilla and germinal matrix. The hair’ root begins here, anchoring the strand to the follicle. The hair bulb is the “living” part of the hair, where cell division occurs. It also contains hormones that activate at certain life stages, like puberty, to stimulate different hair changes.
The hair bulge acts as a reservoir for epidermal stem cells, crucial to regenerating the hair follicle. It is found in the middle of the follicle and serves as an insertion point for the arrector pili muscle. The arrector pili help our skin to regulate heat.
Where are the hair follicles located?
The short answer to this is – hair follicles are found everywhere. Wherever there is hair on your body, you will undoubtedly have hair follicles on the skin. But where exactly are they in the body?
Human skin has three layers, and follicles usually originate in the first and second layers (epidermis and dermis). Some hair grows from the third layer (subcutaneous tissue), such as on our scalp, and terminal hair, such as eyelashes and eyebrows.
The hair growth cycle
There are four different stages to a normal hair cycle. Not all strands are at the same stage, even if they are located near each other. Let’s take a quick look at how new hair grows at each stage:
1. Anagen (The Growth Phase)
The first stage is the anagen phase, which lasts for 3 to 7 years. Hair continues to grow until trimmed or falls out on its own accord. About 85% of hair found on a healthy scalp is in this current growth phase.
2. Catagen (The Regression phase)
In the second stage, hair growth begins to slow down. The hair follicle shrinks, and the hair shaft separates itself from its base over a few weeks.
3. Telogen (The Resting Phase)
About 15% of hairs on the scalp are in the third stage, known as the Telogen phase. This resting phase lasts about 3 months and is the period when hair is not actively growing. Researchers think this period is a particularly crucial phase for hair because a hive of cellular activity happens to stimulate regeneration and prepare the follicle for a return to the anagen phase once more.
4. Exogen (The Shedding Stage)
The fourth and final stage of hair follicle cycling is the exogen phase, which lasts 2 to 5 months. This is an extension of the telogen stage and sees hair fall out of the root. Often called club hair, we lose between 50 to 100 strands daily.
How big is a hair follicle?
Hair follicles are microscopic, so you cannot see them with the naked eye. There are certain things, though, that influence their size. Different body parts have different-sized cells, e.g., hair follicle cells on your scalp will be different than on your chest.
Secondly, people of different races may have differently sized and shaped follicles. Caucasian people, for example, often have elongated follicles that help produce straight or wavy hair. Black people have curvier-shaped follicles, resulting in tightly curled hair.
What is the function of hair follicles?
Only by understanding the critical function of hair follicles will you go that extra mile to support them. So what exactly is their purpose? Think of them as the brains of the hair, responsible for a range of things, including shape and appearance, color, and hair growth.
Different follicles produce different hair types, depending on their location. This is why our scalp hair differs from chest hair, etc. Furthermore, shape defines what texture of hair we grow.
Hair gains pigment color from melanin, which you can find in follicular cells. There are two types of melanin found in hair; eumelanin and pheomelanin.
A large amount of eumelanin results in black hair, while a medium amount produces brown. Tiny amounts cause blonde, while pheomelanin makes red hair. As you grow older, you may be unable to maintain the same level of melanin, leading to greying hair.
Follicles regulate hair growth, including the four stages of hair development (Anagen, Catagen, Telogen & Exogen). On average, hair will grow at around half an inch per month.
Hairs will typically regrow after being pulled from their follicles. But a damaged follicle will be unable to grow new hairs. Alopecia and other hair loss conditions can further prevent follicles from functioning normally.
4 common issues affecting hair follicles
So many hair loss conditions stem from poor hair follicle health. Only by visiting your doctor and a dermatologist can you safely get answers as to why your hair follicles are in trouble.
Below are four of the most common conditions:
- Alopecia areata
Also known as spot baldness, alopecia areata is an autoimmune disease that sees your immune system attacking hair follicles. It mistakes them as foreign cells, resulting in sudden hair loss in large cluster areas.
If left unchecked, this condition can develop into alopecia universalis, a complete hair loss across your body. Although there is no cure for alopecia areata, there are treatments and medications which can help alleviate symptoms and slow progression.
- Androgenetic alopecia
Androgenetic alopecia, also known as male pattern baldness, is a widespread condition that affects approximately half of men aged 50 and over in the UK. This condition causes the hair growth cycle to slow, resulting in shorter, more brittle hair. Over time, the hair follicle becomes less efficient and will eventually be unable to support new strands.
- Telogen effluvium
Another common cause of hair loss that affects hair follicles is telogen effluvium, which causes hair to drastically thin, shed, and fall out. It is typically more common in women than in men.
High levels of stress can trigger telogen effluvium. This might include suffering from burn-out or exhaustion, undergoing surgery, becoming sick, physical trauma, or giving birth. You can also suffer from it when switching to certain medications.
Sufferers will lose patches of hair across random parts of their scalp, eyebrows, legs, and facial hair. Although the effects of telogen effluvium are reversible, it is still wise to see your doctor and establish the root causes of this sudden hair loss.
- Hair follicle infection (Folliculitis)
Folliculitis is an inflammation that creates a rash of tiny bumps on your skin. It can affect any part of your body. Spots can become sore and itchy, range in colour from white, yellow, and red, and may contain pus.
There are many causes of folliculitis. The most common include bacterial infection (staphylococcus aureus), a virus, fungi, or inflammation from ingrown hairs. Although folliculitis can fade without treatments, doctors can help you manage symptoms with topical or oral solutions.
What tests are used to assess the health of the hair follicles?
As with any condition, your doctor will want to examine your scalp closely and consider your health and medical history when diagnosing you. Some tests are used to get additional information, including:
- Blood test – the primary diagnostic tool used to check hair condition. Tests may involve a complete blood count, an ANA test (to detect autoimmune diseases), and a c-reactive protein test (to check infections and inflammation).
- Biopsy – A small tissue sample is extracted from your skin and sent to a laboratory for microscopic examination.
- Pull test – This simple test sees your doctor pull a section of your hair. They will examine its strength and if and how many strands come out.
Can you stimulate hair follicles to grow new hair?
Hair loss sufferers often wonder if you can regrow hair by stimulating hair follicles back into action and avoiding invasive procedures. Unfortunately, damaged hair follicles cannot grow hair; there’s no known way to change this.
That said, research is ongoing. One of the most promising areas is stem cell therapy, which could potentially revive follicles – though further testing is required. You can keep up to date with the latest information on stem cell hair transplants here.
Presently, the most effective treatment which yields permanent results is hair transplantation. This is a simple procedure where a specialist transfers healthy hair follicles strategically into targetted areas suffering shedding or baldness.
You can strengthen existing follicles with certain products and treatments, including essential oils, caffeine shampoos, massage therapy, medications like minoxidil, and Platelet Rich Plasma (PRP) injections.
Despite their tiny size, hair follicles play an enormous role in how our hair grows. It keeps strands looking firm, strong, and thick. Think of them as essential building blocks. You can only begin to correct and repair hair loss damage by recognizing the importance of a healthy follicle. They are the foundation for stimulating new growth and restoring your scalp to its former glory.
The primary function of a hair follicle is to grow your hair. The follicle stimulates cell growth and allows for angiogenesis (which creates new blood vessels). They also contain specialized cells which enable them to self-renew, regulate growth and maintain their structure.
Hair follicles form in the first and second layers of your skin and are made up of several layers of cells originating from basal cells in the epidermis. Hair matrix cells split, creating different layers.
Yes, a hair follicle can close, leading to permanent hair loss in that area. There are many reasons a follicle might close; the two most common include malnourishment (a lack of vital nutrients) and physical trauma, like repeated hair pulling. Some medications, like minoxidil (known as rogaine), can react and stimulate dormant hair follicles. That said, you must continue to use these medications to maintain results.
- Heather L. Brannon, MD: The Structure and Growth Cycle of Hair Follicles https://www.verywellhealth.com/hair-follicle-1068786
- National Library of Medicine. Hair Follicle Anatomyhttps://medlineplus.gov/ency/imagepages/9703.htm
- Folliculitis. American Osteopathic College of Dermatologyhttp://www.aocd.org/skin/dermatologic_diseases/folliculitis.html