Hair type typically refers to the curl pattern. There are four main hair types: straight, wavy, curly and coily. Straight: This includes hair that has no or a very subtle bend in the hair. This is commonly referred to as 1a, 1b and 1c hair. Wavy: This includes type 2a, 2b and 2c hair. All have waves in elongated “S” shapes that start either at the root or a few inches below. Curly: This includes type 3a, 3b and 3c hair. Curly hair has spirals and ringlets that begin at the root, and they typically vary in tightness. Coily: This includes 4a, 4b and 4c hair, all of which have tight spirals and ringlets in “S” or “Z” shapes. If you need help determining your curl pattern (hair types 2-4), check our guide to determining curl types .

What is hair texture?

Hair texture typically refers to how thick each individual strand is. Texture is categorized into three types: fine, medium and thick/coarse. Fine : This is the softest yet most fragile hair texture because the individual strands are thin. Those with fine hair may notice that using less product is more, it may be harder to hold styles (it tends to fall flat) and hair may get oily quickly. People with this hair texture may want to look for thickening and volumizing products to address these concerns. Medium : Unlike fine hair, medium hair texture is thicker and slightly more resistant to damage and breakage. Medium hair textures are easier to style than fine hair, but may have more frizz. Thick/coarse : The thickest of all hair textures, they have the most resiliency to heat and hair treatments and are less susceptible to breakage. They also hold styles the best, but are the most prone to frizz and dryness.

What is hair porosity?

Hair porosity refers to how well your hair absorbs and retains moisture. It is typically categorized into three types: low, medium and high. Low porosity : The hair cuticles are tightly packed, making them resistant to absorbing moisture. That means products in general may sit on the surface of the hair rather than absorb into it (the same goes with water). Hair may have a harder time absorbing products since it already has a high level of moisture to start with. Some individuals may not know they have low porosity until they notice a lot of buildup in their hair. You’ll want to find hair care items that are water-based, protein-free or have ingredients like glycerin that attract moisture. Medium porosity : The hair cuticles are slightly open and there’s more balance between absorption and retention. This type is the easiest to manage and maintain. It may also feel much healthier than hair with high porosity. High porosity : The hair cuticles are either very open or damaged, which causes the hair to absorb moisture quickly but lose it just as fast. For example, hair usually dries right when you get out of the shower. This hair type often requires extra hydration and protective care, such as incorporating a heat protectant to prevent further damage to the cuticle. Your hair will also feel dry and dull; it will soak up all oils and proteins, but unless you use the correct products, the hair will not retain moisture. High porosity hair will benefit from products with moisturizing and sealing ingredients, such as oils and butters, to close the cuticles and lock in moisture. It is possible to have different porosity levels due to getting highlights where only 30% of the hair was damaged. Most fully color-treated hair will have high porosity because of damage to the cuticle, while most virgin hair (that doesn’t have any color) usually has lower porosity.

Hair Care Glossary: The Most Common Hair Terms Explained

By Bianca Alvarez, Associate Reporter

Shopping for hair care can be daunting, whether you’re a beginner navigating the packed hair aisle at the store or a beauty enthusiast who wants to try everything and anything. With so many terms and ingredients to know about, it’s important to know what works best for you and your hair type, texture and specific concerns like dry hair and oily scalps.

To help you better understand common hair care terms and ingredients, I created this glossary, guided by hair care experts and our extensive coverage. Bookmark this page: I’ll be updating this periodically with more hair care ingredients found in shampoos, hair masks, hair oils and more.

Want more from NBC Select? Sign up for our newsletter, The Selection, and shop smarter.

Frequently asked questions

Hair type typically refers to the curl pattern. There are four main hair types: straight, wavy, curly and coily.

Straight: This includes hair that has no or a very subtle bend in the hair. This is commonly referred to as 1a, 1b and 1c hair.
Wavy: This includes type 2a, 2b and 2c hair. All have waves in elongated “S” shapes that start either at the root or a few inches below.
Curly: This includes type 3a, 3b and 3c hair. Curly hair has spirals and ringlets that begin at the root, and they typically vary in tightness.
Coily: This includes 4a, 4b and 4c hair, all of which have tight spirals and ringlets in “S” or “Z” shapes.

If you need help determining your curl pattern (hair types 2-4), check our guide to determining curl types.

Hair texture typically refers to how thick each individual strand is. Texture is categorized into three types: fine, medium and thick/coarse.

Fine: This is the softest yet most fragile hair texture because the individual strands are thin. Those with fine hair may notice that using less product is more, it may be harder to hold styles (it tends to fall flat) and hair may get oily quickly. People with this hair texture may want to look for thickening and volumizing products to address these concerns.
Medium: Unlike fine hair, medium hair texture is thicker and slightly more resistant to damage and breakage. Medium hair textures are easier to style than fine hair, but may have more frizz.
Thick/coarse: The thickest of all hair textures, they have the most resiliency to heat and hair treatments and are less susceptible to breakage. They also hold styles the best, but are the most prone to frizz and dryness.

Hair density is the number of hair strands per square inch on your scalp. It differs from hair thickness, which is the width of the individual strands. Your hair looks thicker or thinner depending on your hair density, and you can have either low, medium or high density.

Low density means your hair is sparse and your scalp is visible
Medium density refers to a more balanced look of the hair and scalp
High density is when your hair is thick and there is no visible scalp

Hair porosity refers to how well your hair absorbs and retains moisture. It is typically categorized into three types: low, medium and high.

Low porosity: The hair cuticles are tightly packed, making them resistant to absorbing moisture. That means products in general may sit on the surface of the hair rather than absorb into it (the same goes with water). Hair may have a harder time absorbing products since it already has a high level of moisture to start with. Some individuals may not know they have low porosity until they notice a lot of buildup in their hair. You’ll want to find hair care items that are water-based, protein-free or have ingredients like glycerin that attract moisture.
Medium porosity: The hair cuticles are slightly open and there’s more balance between absorption and retention. This type is the easiest to manage and maintain. It may also feel much healthier than hair with high porosity.
High porosity: The hair cuticles are either very open or damaged, which causes the hair to absorb moisture quickly but lose it just as fast. For example, hair usually dries right when you get out of the shower. This hair type often requires extra hydration and protective care, such as incorporating a heat protectant to prevent further damage to the cuticle. Your hair will also feel dry and dull; it will soak up all oils and proteins, but unless you use the correct products, the hair will not retain moisture. High porosity hair will benefit from products with moisturizing and sealing ingredients, such as oils and butters, to close the cuticles and lock in moisture.

It is possible to have different porosity levels due to getting highlights where only 30% of the hair was damaged. Most fully color-treated hair will have high porosity because of damage to the cuticle, while most virgin hair (that doesn’t have any color) usually has lower porosity.

Our favorite hair care products

Best for fine hair: K18 Leave-In Molecular Repair Hair Mask

K18 Leave-In Molecular Repair Hair Mask

$75.00

What we like

Available in multiple sizes
Improves manageability
No rinsing needed

Something to note

Higher price point

“My hairstylist started using the K18 hair mask on me during cut and colors back in 2021 and now, I use it at home regularly,” says NBC Select editorial director Lauren Swanson. “It somehow makes my fine, straight hair feel stronger and smoother without weighing it down — like a deep treatment that actually gets it.”

This color-safe reparative hair mask has peptides to reconnect the bonds in your hair that have been broken due to bleaching, heat damage and chemical treatments, according to the brand. By reconnecting them, it can strengthen your hair while also improving its elasticity.

Best scalp treatment: Ouai Scalp Serum

Ouai Scalp Serum

$52.00

What we like

Improves scalp hydration
For all hair types
Can use on wet/dry hair

Something to note

Higher price point

Ouai’s multitasking scalp serum balances the scalp, soothes it and makes your hair appear fuller and thicker, according to the brand. “I massage it into my part and hairline (where my hair is the sparsest) before bed and rinse it out in the morning when I wash my hair,” says NBC Select updates editor Mili Godio, who has fine, wavy hair. “It makes my hair look so much thicker and helps cover those sparse areas. Plus, it doesn’t make my hair look oily or greasy like so many other scalp serums do.”

Best for wavy hair: Lush Super Milk Conditioning Hair Primer

Lush Super Milk Conditioning Hair Primer

$22.00

What we like

Improves shine
Long-lasting scent
Reduces frizz

Something to note

Only sold on Lush’s site

This leave-in conditioner, which doubles as a heat protectant and detangler, is perfect for my dry, damaged, medium-thick and wavy hair. The creamy conditioner helps soften and moisturize my hair without weighing down my waves and instead helps define them. Plus, a little goes a very long way — despite using this spray regularly, I’ve barely made a dent in the bottle, which makes it worth the splurge, in my opinion. (Ed’s note: The inclusion of products sold by Lush in this article was made independently of Evans.)

Best for curly hair: 4U by Tia Clarifying Shampoo

4U by Tia Clarifying Shampoo

$9.97

$11.99

What we like

Non-drying
Reduces frizz
Improves dullness

Something to note

Nothing to note at this time

NBC Select editorial projects manager Rebecca Rodriguez uses this clarifying shampoo once a week to remove product buildup from her thick, curly hair. “My hair always feels lightweight and clean after I use this,” she says. The sulfate-free shampoo has apple cider vinegar to clarify and stimulate the scalp, sea moss extract to add strength and shine to the hair and hemisqualane (a silicone alternative) to nourish the hair and define waves, curls and coils.

Best for natural hair: Olaplex No. 5 Bond Maintenance Conditioner

Olaplex No. 5 Bond Maintenance Conditioner

$32.00

What we like

Moisturizing
Maintains hair health
Improves manageability

Something to note

May be hard to squeeze out

Although you would typically wash out this conditioner in the shower, NBC Select associate SEO reporter Ashley Morris loves using it as a leave-in hair mask to treat her natural, damaged hair. “[It] helped to restore moisture and shape to my small curls,” she says. “It took months, but I was able to treat the heat-damaged sections and minimize breakage with the help of this conditioner.”

Hair care terms to know

Biotin

Biotin is a B vitamin that promotes hair growth and strength. While it won’t make your hair grow faster, it will help prevent breakage and make your hair look fuller, feel stronger and appear healthier. Biotin is also great for giving your hair extra support and shine, especially if it feels and looks weak or thin.

Where to find it: supplements, shampoos, conditioners, hair masks and serums.

Best for: all hair types, but especially for anyone dealing with hair thinning or damage.

Expert tip: You can also get biotin from foods like eggs, nuts and salmon.

Castor oil

Castor oil, a nutrient-rich oil from the castor bean plant, is packed with ricinoleic acid, a fatty acid known for its moisturizing, antibacterial and anti-inflammatory properties. It also promotes hair growth, prevents breakage, soothes the scalp and adds thickness and shine.

Where to find it: hair growth oils or serums, moisturizing shampoos, deep conditioners and scalp and anti-dandruff treatments.

Best for: those with medium and thick hair. If you have fine or thin hair, this thick oil can cause buildup and weigh it down, so either avoid using castor oil or thoroughly wash it out to prevent any residue.

Expert tip: If you have a sensitive scalp, do a patch test before applying it to your scalp to avoid a reaction. When using castor oil in a scalp treatment, massage it into your scalp to stimulate circulation and absorption.

Keratin

Keratin is a natural protein found in your hair, and it’s often added to hair products to help repair damage, smooth frizz and boost shine. It works by filling in the tiny cracks or weak spots along the hair shaft, helping to strengthen and smooth the cuticle.

Where to find it in hair products: keratin treatments, masks and strengthening shampoos.

Best for: frizz-prone, damaged or chemically treated hair.

Expert tip: Too much keratin can make hair stiff, so balance it with moisture. Use it consistently for at least two weeks to start seeing visible repair. Once the hair begins to strengthen and improve from the added protein, it’s essential to follow up with a hydrating conditioning mask, which helps prevent the hair from becoming too stiff or brittle due to excess protein.

Minoxidil

Minoxidil is an FDA-approved topical treatment for hair loss. It increases blood flow to stimulate hair growth and helps thicken hair over time.

Where to find it: it is the active ingredient in Rogaine and similar hair regrowth serums, foams or prescription-strength treatments.

Best for: those with androgenetic alopecia (pattern baldness) or experiencing excessive hair shedding or thinning. It is not for anyone experiencing temporary hair loss or looking for a quick fix.

Expert tip: It takes around three to six months to see results as long as you are consistently applying it every day.

Men’s Rogaine 5% Minoxidil Foam

$33.34

$43.49

Amazon

Rogaine Women's Hair Regrowth Treatment

$34.98

Amazon

Hers Hair Regrowth Treatment

$33.99

$39.99

Amazon

Hims Hair Regrowth Treatment

$28.98

Amazon

Parabens

Parabens are preservatives found in hair products’ packaging to prevent bacteria, mold and other microorganisms from growing. While they serve a functional purpose in manufacturing, they don’t provide any direct benefit to the health of your hair or scalp. They can also cause build-up and irritation with repeated use.

Where to find it: shampoos, conditioners and styling products.

Best for: anyone without scalp sensitivity.

Expert tip: When possible, search for products that are paraben-free to avoid any potential issues for both your scalp and hair. You can tell build-up is occurring when your hair starts to feel heavy and it looks flat, dull or greasy, even after washing it. Scalp irritation from parabens is not as common; however, it does have the potential to cause a reaction.

Rosemary oil

Rosemary oil is an essential oil with anti-inflammatory and antimicrobial properties. It strengthens the hair, promotes scalp health and hair growth, balances oil production and combats dandruff and dry scalp.

Where to find it: serums, oils, treatments and anti-dandruff products.

Best for: those looking to improve scalp health.

Expert tip: You should always dilute rosemary oil since it can irritate sensitive scalps. Add one to two drops of rosemary oil to your favorite shampoo or combine it with a carrier oil like coconut or jojoba oils to avoid irritation. Use it two to three times a week for hair growth (most people see benefits after two to three months of consistent use).

Sebum

Your scalp naturally produces sebum (an oily substance) to moisturize and protect it. Sebum helps protect your hair and scalp against dryness, breakage, bacteria and environmental damage. If there’s an imbalance in your natural sebum production, your hair follicles can become clogged, leading to greasy, oily, damaged and flaking hair.

Expert tip: Incorporate a gentle, sulfate-free shampoo, lightweight hair oils and scalp massages into your routine to balance sebum.

Silicones

Silicones act as a protective coating that helps make hair more manageable, shinier and frizz-free. While silicones may make your hair feel silky, they can cause product buildup over time.

Where to find it: conditioners, serums, heat protectants and styling creams.

Best for: people with straight or high-porosity hair who may benefit from the added shine and protection. They’re best for medium, thick, coarse, straight and wavy hair (silicones may way down fine and curly hair types).

Expert tip: If your hair feels heavy or greasy, it might be because of silicone buildup. Use a clarifying shampoo to reset your hair.

Sulfates

Sulfates are a cleansing agent that makes shampoos and other hair products foam up. However, they’re known for stripping dirt and natural oils from your hair, so choose a sulfate-free hair product when possible.

Where to find it: some shampoos and clarifying products.

Best for: Most people should avoid sulfates, specifically those with curly, color-treated, or dry hair types, since sulfates can be too harsh.

Expert tip: When shopping, you may come across sodium lauryl sulfate (SLS) and sodium laureth sulfate (SLES), which are the two most common types of sulfates. Instead, look for more gentle alternatives like sodium cocoyl isethionate, apple cider vinegar, cocamidopropyl betaine and sodium lauryl sulfoacetate (SLSA).

Meet our experts

NBC Select, we work with experts who have specialized knowledge and authority based on relevant training and/or experience. We also take steps to ensure all expert advice and recommendations are made independently and without undisclosed financial conflicts of interest.

Daisy Evans is a hairstylist and lead of Lush hair and Lush HairLab, the brand’s first stand-alone hair salon in Brighton, United Kingdom.
Christine Bellemare is a hairstylist and co-owner of Maven A Collect, a hair salon in Boston.
Jae Manuel Cardenas is a senior Stylist at Ollin Salon NYC by Johnny Ramirez.
Sophie Rose Gutterman is a Los Angeles-based celebrity hairstylist specializing in curly hair.
Jennifer Thomas is a SH-RD ambassador and celebrity hair stylist.

Why trust NBC Select?

I am an associate reporter at NBC Select covering beauty, including new product launches and articles such as the best blow dryer brushes and dry shampoos. For this piece, I interviewed five hair experts to define each term. I also gathered information about who should use each ingredient, where to find them and any relevant expert tips and guidance.

Catch up on NBC Select’s in-depth coverage of tech and tools, wellness and more, and follow us on Facebook, Instagram, Twitter and TikTok to stay up to date.

Bianca Alvarez

Bianca is an associate reporter for NBC Select, where she covers the latest product launches and all things relating to wellness and personal care. She joined the team in 2023 and now works on skin care and wellness guides, odes and gift guide roundups, along with deals and sales. When she’s not covering skin care or hair care, you can find her trying out new beauty products, scrolling through TikTok, watching sports and hanging out with her friends and family.