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What is Hair Made Of?

All Hair Types

What is Hair Made Of? What is Hair Made Of? What is Hair Made Of?

We’ve taught you a lot about hair—from summer hair protection guides to the latest hair color trends. And while you may have perfected your hair care and hairstyling routines, there’s one hair basic we’ve yet to fill you in on: hair anatomy! Ever wonder what hair is made of? While there’s a lot that goes into it, we promise learning about your hair’s structure doesn’t have to be overwhelming. As proof, we’re making it easy for you with our very own hair structure breakdown. You’ll be a hair science wiz in no time!


When it comes to hair anatomy, we won’t lie and say there isn’t a lot to know. The truth is, your hair is a lot more complicated than you might think. Let’s start with the basics: your hair grows from a root, located in the bottom of the hair follicle, which is made up of cells of protein, according to the American Academy of Dermatology. Got it? This protein, also known as keratin, makes up both your hair and nails, and is also a main protein in your skin, per the Cleveland Clinic. Yes, you read that right—your hair is made of protein!


Now that you know what hair is made of, let’s dive into a breakdown of your hair structure. This is where things can get a little tricky, so we’ll keep things as simple as possible while laying out everything you need to know about the key components of your hair. Let’s get to it!

Your hair and its structure, as you can probably guess, is centered around your hair follicle. This follicle begins at the surface of the epidermis (a layer of your skin) and extends into the dermis (a deeper layer of your skin), according to a study from the National Center for Biotechnological Information (NCBI).

The hair follicles on your head can be broken into three segments, per the NCBI study: the infundibulum, the isthmus, and the inferior segment (lower follicle). Additionally, each follicle has an attached sebaceous gland and arrector pili muscle (more on those later).

The infundibulum segment, according to the NCBI study, begins at the surface of the epidermis and extends to the opening of the sebaceous gland duct. The NCBI study goes on to explain that the isthmus is the area between the sebaceous duct opening and the bulge—the area of the hair follicle with the insertion of the arrector pili muscle. The inferior segment of the hair follicle extends from the bulge to the base of the hair follicle, including the bulb.

So, what exactly is this bulb? The bulb contains the follicular matrix surrounding the sides and top of the dermal papilla. The dermal papilla contains capillaries and interacts with the matrix, which is the part of the hair follicle where cells reproduce to form the hair shaft. Melanocytes, which provide the hair shaft with color, are also intermixed with the matrix.  

Ready to learn more about the hair shaft? We thought so. Let’s start from the inside, out. At the core of the hair shaft is the medulla, which is surrounded by the cortex. Next, we have a single layer of cells that make up the shaft cuticle, which itself is surrounded by three layers to form the internal root sheath, according to the NBCI study. Whew! Still with us? All of those layers of the hair shaft are encompassed by the external root sheath.

You’re almost a hair anatomy expert! Remember the sebaceous gland and arrector pili muscles we mentioned earlier? Well, they’re there for a purpose. The NCBI study states that the sebaceous gland produces a lipid-rich sebum that protects the hair. Furthermore, the arrector pili muscles are attached to the bulge and papillary layers of the dermis, resulting in goosebumps when the weather gets cold and the muscles contract.

Next up: Once you learn about your hair’s structure, it’s only a matter of time before you start questioning how it grows—and how you can make it grow faster. If you’re already wondering about hair growth, here’s The Truth About How to Grow Hair Faster.