Hair Breakage 101: Why It Happens and What You Can Do About It

If your ends look wispier than they used to, or your ponytail feels thinner even though you haven't cut your hair in over a year, breakage is often the reason—meaning, it’s not a growth problem. Hair breakage is common, but you can do something about it. Understanding why it happens is the first step to protecting the length you're already growing.

It helps to start here, because the two get confused constantly. Shedding is a normal part of the hair growth cycle: A healthy adult sheds up to 80 to 100 telogen (resting-phase) hairs a day, often more on wash days.¹ Those hairs come out at the root, typically with a small white bulb at the end.^9,10

Breakage is different. It happens when internal cracks accumulate along the hair shaft from repeated stress, and the strand eventually snaps at one of those weak points—not always at the root, and not on any predictable schedule.⁸ Instead of one hair path from root to tip, you may notice more flyaways, more visible split ends, and a "fringe" of shorter, uneven pieces scattered throughout your length rather than just at your hairline.

Breakage is rarely caused by one thing. It's usually the buildup of everyday stress across four categories:

Mechanical stress. Brushing, combing, tight hairstyles, and friction from pillowcases or collars gradually wear down the cuticle—the hair's outer protective layer—creating fragile points along the hair shaft until it eventually lifts and splits.⁸

Thermal stress. Blow-dryers, flat irons, and curling tools use high heat to temporarily rearrange the hydrogen and disulfide bonds that give hair its structure. Blow-dried hair typically shows noticeably more surface damage than air-dried hair, and flat-ironing can overheat and weaken the shaft enough to cause it to rupture.¹¹ Heat protectants can genuinely help: Certain polymer-based formulas have been shown to significantly reduce breakage from combing after hair is thermally stressed.^4,12

Chemical stress. Coloring, bleaching, and other chemical treatments work by altering the hair's internal structure, which inevitably strips away some of its natural protection in the process.^13,14

Environmental stress. Continuous sun exposure is one of the most damaging—and hardest to avoid—factors in hair breakage. UV light triggers photo-oxidation that leads to dryness, roughness, and visible sun damage over time.^2,3

Aging. As we age, our hair spends less time in its active growing phase and individual strands tend to become finer, with fewer protective cuticle layers—which may make them more prone to breaking.^15,16,17 Gray and white hairs add another layer of complexity: they carry less of the internal lipid that keeps a fiber flexible and sealed,¹⁸ so they tend to feel less smooth and can be more susceptible to wear and tear. Bleaching, heat styling, and chemical treatments can compound with age-related changes, making it even harder to keep your hair looking and feeling healthy.^19,20 

Porosity is your hair's ability to absorb and hold onto moisture, and it's one of the biggest factors in how breakage-prone your hair is.^4,13,21 Low-to-medium-porosity hair has a smooth, sealed cuticle and an intact outer lipid layer—it retains moisture well and tends to look shiny and manageable. High-porosity hair, usually the result of heat, chemical treatments, or ongoing wear, has an open, lifted cuticle with little lipid protection left.^5,6 It absorbs moisture quickly, loses it fast, and is significantly more prone to dryness, breakage, frizz, and split ends.²¹

Damage doesn't just make hair look worse in the moment. It can change hair's internal structure and porosity going forward, which affects how well any product you use can actually work.⁴

If you have curly or coily hair, you may already know it takes more damage from the same routine that would barely touch straight hair—and there's a structural reason for that. Coily hair has a helical shape and a flattened, elliptical cross-section that make it inherently more prone to mechanical damage than straight hair, and common styling practices like heat, chemical relaxers, and tight braiding can compound that vulnerability over time.^7,8 Research on how chemical and physical damage affects coily hair porosity specifically is still catching up, which is exactly why a gentler, more protective routine matters even more for textured strands.⁴

Because breakage builds up gradually, it can also improve gradually in ways that are easy to miss day to day. A few simple habits make it easier to actually see what's changing:

This is exactly why we created Strand Serum. It's a physician-formulated serum developed with input from a board of dermatology partners as part of Nutrafol's ongoing clinical research, built around a patent-pending, bi-phase DualFusion™ Complex—an oil phase and a water phase that work at the cuticle and the cortex at the same time, rather than addressing just one layer of damage. The formula was tested on chemically treated, color-treated, and chemically straightened hair, and on all hair types (including straight, wavy, curly, and coily hair).

The oil phase (built on Hemisqualane and Rosehip Fruit Extract) helps replenish the hair fiber's protective lipid layer. The water phase (built on Milk Thistle Seed Extract and Wild Olive Extract) helps strengthen from within the cortex and improves resilience.

In clinical testing, Strand Serum reduced breakage by up to 64% after use on both damp and dry hair, and by up to 83% with continued use over time.^† It was also tested to reduce visible split ends by 62%, leave hair up to 6 times stronger, protect against heat up to 450°F, and control frizz for up to 72 hours.^† Independent surface imaging (SEM) also showed visibly smoother, less-cracked cuticles after use, offering a literal picture of the formula at work.

Strand Serum is tested on all hair types and textures, and is formulated for high-porosity, damaged, color-treated, or chemically treated hair. To use it: Shake well. Start with 2 to 3 drops (up to 15 as needed) in your hands, and apply to towel-dried mid-lengths and ends after washing and conditioning. Then comb through and style as usual. It layers easily into a full routine with other scalp care. It can also be used alongside Nutrafol Hair Growth Nutraceuticals, which support several key root causes of hair thinning from within.

Hair breakage happens when everyday stress accumulates faster than hair can protect itself—and it's easy to mistake for a growth problem when it's really a length-retention one. Porosity is the throughline: The more damaged and porous a strand becomes, the more breakage-prone it is, with coily hair especially vulnerable to the mechanics of everyday styling. Simple habits like tracking your ends over time and using ingredients that genuinely support the hair fiber, like a good conditioner, can make a real difference—and Nutrafol Strand Serum was built specifically to strengthen and protect strands at the cuticle and cortex simultaneously, with a clinically tested 83% reduction in breakage over time.^†

What's the difference between hair breakage and hair shedding? 

Shedding is hair falling out at the root as part of the natural growth cycle—up to 80 to 100 hairs a day is typical. Breakage is a strand snapping partway along the shaft or at the ends, usually from accumulated damage.^1,22

What are the most common causes of hair breakage? 

The main drivers are mechanical stress (brushing, tight styles), thermal stress (heat tools), chemical stress (color, bleach), and environmental stress (UV exposure, pollution)—often in combination rather than one at a time. To support, Strand Serum protects against mechanical stress and thermal stress, and was tested on chemically treated, color-treated, and chemically straightened hair, and on all hair types (including straight, wavy, curly, and coily hair).

Does coily or curly hair break more easily than straight hair? 

Yes. Textured hair's helical shape and flattened cross-section make it structurally more prone to mechanical damage, and common styling practices can add to that vulnerability over time.⁴

How can I tell if my hair porosity is contributing to breakage? 

High-porosity hair typically feels less smooth and moisturized, and shows more frizz, dullness, and split ends—all signs the cuticle has little of its protective lipid layer.⁴

How long does it take to see less breakage? 

Because breakage is cumulative, improvement is usually gradual. In clinical testing, Nutrafol Strand Serum showed a 64% reduction in breakage after one use on both damp and dry hair, improving to up to 83% with continued use over time.^†