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Most of us know our hair types. After years of styling and caring for our hair, we can pretty easily determine whether our hair is thin and fine, thick and coarse, or something in the middle—right?
Wrong. That's because whether you have thin vs. thick hair is a combination of factors: hair thickness and hair density. Although many people conflate thickness and density, they're entirely different measurements that together determine your hair type: how it behaves, what it needs, and how to style it for best results.
What does this all mean? It means you may have hair that's both coarse and thin or fine and thick. In other words: Everything you thought you knew about your hair may be totally wrong.
We spoke to four experts in hair care to learn the difference between hair thickness and density to help you determine your hair type, once and for all.
Keep reading to find out whether you have thin vs. thick hair (for real, this time.)
Hair Thickness vs. Hair Density
According to Eric Spengler, beauty industry consultant and former senior vice president at Living Proof, hair thickness refers to the diameter of your individual hair strands. If you're wondering how to determine what is fine hair and coarse hair, there's a distinct, measurable difference between the two.
"Hair with a small diameter—or fine hair—has a typical diameter of about 50 microns," Spengler explains. "Hair with a larger diameter—or coarse hair—has a typical diameter of about 120 microns."
For comparison's sake, a piece of copy paper is 70 microns thick. "Fine hair is almost half the thickness of copy paper, and coarse hair has about twice the thickness of copy paper," Spengler says.
Hair density, on the other hand, refers to the amount of hair on your head. Just as hair thickness can vary wildly from person to person, so, too, can hair density.
"Those with thin hair might have about 80,000 fibers on their head, and an individual with thick hair will have about 150,000 fibers," Spengler says. "The greater the number of fibers, the greater the interaction between each fiber." In other words, dense hair usually looks and feels fuller than thin hair.
Spengler adds that people "often confuse the diameter of each fiber with density and call it 'thin hair.' This is more appropriately called 'fine hair.'"
Hair thickness and density don't necessarily correlate, which is why hair can be coarse and thin—and the thick vs. thin issue is frequently muddled.
According to Harry Josh, celebrity hairstylist, colorist, and creator of Harry Josh Pro Tools, it's worth spending time understanding your hair thickness and density. "It’s important to know how thick and dense your hair is to be able to determine the best products, cuts, and styles to work for you," he says.
How to Determine Hair Thickness
Now that we've nailed down the difference between fine and coarse hair, take a look at your strands.
According to Spengler, the best way to determine your hair thickness is to feel and look at it. If it's coarse, it will feel dry and rough to the touch. "Since hair is mostly protein, coarse hair has significantly more protein, so that it will feel stiffer," Spengler notes.
What if you suspect your hair is in the fine or medium category? "An easy way to figure out what type of hair you have is to look at a strand that has come out in your hairbrush and hold it between your fingers," Josh says. "If you can barely feel it, you probably have fine hair."
If your strands feel neither wispy nor rough, you can assume you have medium hair thickness.
Hairstyles for Fine vs. Coarse Hair
If you have fine hair, a cut with lots of layers may not be your best look. "Avoid cutting layers into fine hair because this will decrease the volume even more," says Kari Williams, a board-certified trichologist, licensed cosmetologist, and member of DevaCurl’s Expert Curl Council.
Fine hair benefits from "blunt haircuts to create clean lines and the illusion of thickness," Josh says.
If you have coarse hair—especially curly, coarse hair—Josh recommends avoiding single-length cuts. "Layers and added texture will take the bulk out and give hair more natural movement," he suggests.
How to Measure Hair Density
To figure out whether you have low- or high-density hair, do the ponytail test.
"Create a ponytail with your hair, and if you can wrap the elastic only once, it's thick, both in terms of the number of fibers and the diameter of each fiber," Spengler says. "If you can wrap the ponytail with an elastic two to three times, it's medium, and if you need to wrap the band more than three times, your hair is thin. For the latter, it will be coarse if it's damaged."
For more clues about hair density, Rodger Azadganian, founder of AZ Craft Luxury Hair Care and owner of Salon 8 hair salons, recommends looking at your scalp in the mirror. If you have thick hair, your scalp will be barely noticeable underneath your hair; if you have thin hair, your scalp will be quite visible.
Hairstyles for Thin vs. Thick Hair
"With low-density hair, adding volume is key," Josh says. Like with fine hair, haircuts with layers aren't ideal for thin hair. "A blunt cut will give you the appearance of more hair," he suggests.
People with low-density hair should also consider length. "For thin hair, it’s generally a good idea to not wear your hair past your shoulders," Azadganian says. Long cuts "can make thin hair [look] thinner, which results in loss of style."
If you have thick hair, you won't have to worry about your hair looking limp. High-density hair "has a much greater opportunity for each fiber to interact with other fibers nearby, so it's easier to achieve volume," Spengler notes. Thick hair can handle length and layers, which help prevent hair from looking bulky and heavy at the mid-length and ends.
How to Care for Your Hair Type
For the most part, hair thickness and density are genetically predetermined. "Statistically, individuals of Hispanic and African descent have lower hair density than their Caucasian counterparts," Williams says. Caucasians tend to have fine hair thickness, Josh adds.
"But, while density and thickness can vary from person to person, how you take care of your hair can lead to changes in thickness and density," Josh cautions.
No matter your hair type, treating damage can make the most of fine or thin hair and lend smoothness to coarse hair that has become wiry or unmanageable. Try a weekly repairing treatment like Amika The Kure Multi-Task Repair Treatment ($28), which promises to restore the bonds in damaged hair with vegan proteins, castor oil, and sea buckthorn oil.
Likewise, people of all hair types can benefit from lightweight, nourishing oils to moisturize the hair without weighing it down. We like Captain Blankenship Mermaid Hair Oil ($26), made with argan, jojoba, and sunflower oils and scented with cedar and rosemary.
For folks with coarse hair or medium-to-thick density, Spengler recommends cocktailing oil with a leave-in conditioner to tame frizz and increase manageability. Living Proof No Frizz Leave-In Conditioner ($27) is a Byrdie fave that smoothes hair with glycerin, vitamin B5, and glycolic acid.
For folks with fine hair or low density, "opt for products that are formulated to increase volume in the hair and are more lightweight," Williams suggests. Roughing up the cuticle using heat tools or coloring your hair will only make your hair more coarse and damaged. Instead, opt for texturizing products like Verb Volume Dry Texture Spray ($18), which uses rice starch to add girth and grip to hair.
To figure out your hair type once and for all, use the strand and ponytail tests to determine your hair thickness and density. Then, make the most of whatever hair you've got with the proper cut, care, and styling products.