Here's exactly how to fix damaged hair, whether you had a bad dye job or just seem to lose chunks of hair for no reason.
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Your strands go through a lot. There's drying, styling, coloring, plus the ripple effect of daily tension. And to understand just how great of an impact these activities have on your locks' strength — and how to fix damaged hair — you need to wrap your head around some science.

The Science of Hair Damage

"Everyone's strands are made up of proteins [keratin], which contain amino acids held together by three types of chains: disulfide, hydrogen, and ionic," says Mark Curry, the lead chemist at and co-founder of the beauty brand the Inkey List. These bonds vary in their sturdiness and, therefore, what can break them.

Hydrogen bonds are responsible for the shape of our strands — curly, wavy, straight — and are the most breakable, especially since you manipulate them when you style. Ionic bonds provide elasticity — they're easily severed by pH changes from shower water or a hair product with an unbalanced pH (pH isn't listed on labels, so it's hard to tell what might do harm). Disulfide bonds are the strongest and can be broken only by chemicals, like dyes. (Related: The 12 Best Protein Treatments for Stronger, Healthier Hair)

When all these bonds are intact, hair is strong and shiny. But when aggressors — like bleach or heat — break them, hair is fragile, says Curry. It looks unhealthy, too. "It's dull and has ends that snap off or split," says Matt Rez, a celebrity hair colorist and Redken brand ambassador.

Types of Hair Damage & How to Fix Them

How do you fix damaged hair and broken bonds without giving up your highlights and daily hit of the curling iron? Here, experts talk you through the damage done and how you can get back that healthy shine.

Chemical Harm

When you alter your hair color with dye or bleach or the texture with a perm solution or a relaxer, there is a chemical change within the strands' inner core, called the cortex. Do this too often or intensely, and you can cause major damage. The extreme option for how to fix damaged hair: Cut as much off as you can, and start fresh.

Or less drastic: "Get protein treatments at a salon or use protein-based products at home," says trichologist and colorist David Adams. "But it's a process. Expect a year to get strong, soft, and shiny hair again." Try Redken Extreme Anti-snap Leave-In Treatment (Buy It, $22, ulta.com), and once a week, consider applying a bond-building treatment, which has ingredients designed to rebind the atoms in the broken chain. Opt for Olaplex No.3 Hair Perfector (Buy It, $28, amazon.com) to relink disulfide bonds.

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Congested Scalp

The biggest culprits: "Dry shampoo and root touch-up sprays," says Adams. "These sit on the scalp and can clog your hair follicles." (See: How to Use Dry Shampoo the Right Way)

A follicle typically has two or three hairs growing out of it. But when product builds up, follicles shrink, so you get only one or two. As for how to fix damaged hair like this, Adams recommends exfoliating with a scrub like Thicker Fuller Hair Purifying Sugar Scalp Scrub (Buy It, $13, walgreens.com) and using products with zinc, a building block of hair.

You can also clear clogged follicles and promote growth with a professional treatment like the HydraFacial Keravive, which extracts impurities and infuses the scalp with growth factors and protein. (For more budget buys and luxurious picks, check out these scalp scrubs for buildup and beyond.)

Dullness

Think of your hair's outer layer (the cuticle) like a fish's scales. When they lie flat, they reflect light and look shiny. "If some of the cuticle's scales are missing or not lying down because of aggressors like drying, light can't bounce off evenly, and hair looks dull," says Adams. Wondering how to fix damaged hair in this condition? Smooth the cuticle with a leave-in like Aveda Nutriplenish Leave-In Conditioner (Buy It, $37, nordstrom.com). (Steal these pro tips to get that iconic "glass hair.")

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Frizz

"When your hair is damaged, the cuticle opens up and strands tend to get caught on one another, causing frizz and tangles," says Peter Corvington, a hairstylist at Spoke & Weal in New York. How to fix damaged hair like this? Opt for a styling product that will seal the cuticle and protect it from further assaults, like Beachwaver Great Barrier Heat Protectant Hairspray (Buy It, $28, ulta.com). Also, avoid touching your hair, which can rough up the cuticle again, says Adams. (Related: Hair Masks That Combat Dryness and Frizz)

Heat Damage

It's tempting to turn up your curling iron to 450 degrees to get perfect waves fast. But unless you have very coarse, thick locks, that temperature can burn your hair's cuticle and cause breakage. So dial down to 200 degrees and work your way up if needed. Also, look for a protein-based shampoo. "Hair is made up of protein, so that's what it needs for repair," says Adams.

A revitalizing shampoo like Virtue Labs Recovery Shampoo (Buy It, $38, sephora.com) is a go-to solution when it comes to how to fix damaged hair. (As is this three-step leave-in treatment.) A weekly bond-building treatment can help fix heat-damaged hair, too. Try the Inkey List PCA Bond Repair Hair Treatment (Buy It, $13, theinkeylist.com). It has a compound that protects and reconnects all types of bonds.

Friction

Wet hair holds water and stretches. "Healthy hair can stretch three times its original length and then spring back," says Adams. "But an unhealthy strand breaks off when you stretch it with a towel, a brush, or an elastic band."

The solution for how to fix damaged hair like this: "Treat your hair like a fine fabric," says colorist Colleen Flaherty. After washing, wrap hair in an Aquis Rapid Dry Lisse Hair Turban (Buy It, $30, sephora.com), a soft microfiber towel that wicks away water quickly. And swap tight elastics for a silk scrunchie like those from Slip (Buy It, $39 for 3, sephora.com).

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Hair Loss

"When you're stressed, you might stop eating properly and skip exercise, and both of these deficiencies can lead to hair thinning," says Adams. Because of the hair's growth cycle, the loss may occur three months after a stressful event. (Here's how to tell how much hair loss is normal.)

If you're wrapping a hair tie around your ponytail an extra time, "your first step is to reduce stress as much as possible and prioritize rest and good nutrition," says dermatologist Arash Akhavan, M.D. "It could take three months before you see any results." Unfortunately, there's no set answer on how to fix damaged hair here — just keep at those steps.  (That said, you can give one of these shampoos for thinning hair a try.)