Brassy Hair — And Why It’s Not Just a Blonde Problem

I’ve spent the last couple of months bouncing between Mexico City and Tulum—two of my favorite places, but two very different vibes. One has high altitude and drier air; the other’s salty, humid, and full of sun. And somewhere along the way, I started noticing something: my hair color wasn’t quite right.

It looked a little dull. A little too warm. Brassy, even.

And here’s the thing—yes, I’m blonde, and I’m usually the first to notice when my tone goes wonky. But brassiness doesn’t just happen to blondes. It happens to everyone with color-treated hair. Whether you’re brunette, copper, caramel, or platinum, those unwanted tones can sneak in fast. Especially if you’re traveling. Or showering in hard water. Or swimming. Or using the wrong shampoo. Or not clarifying enough. (You get the point.)

So when my friend and fellow hairstylist Sunnie Brook posted her go-to fixes for brassy hair on her Substack, BEAUTY UNDRESSED—and included our Clarifying Hard Water Shampoo + Treatment—I had to share it. Because as much as I love a good toner, what most people need first is a clean slate.

Her post got me thinking about how misunderstood brassiness really is. Most people assume it’s a blonde issue—and sure, blondes are more visibly affected—but brassiness doesn’t discriminate. If you’ve ever colored your hair, you’re likely dealing with it at some point. And even if you haven’t? You might still be experiencing dullness, uneven tone, or a weird shift in shine that all traces back to build-up.

And lately, I’ve been seeing it everywhere. On my clients. On myself. On anyone who's gone too long without a clarifying step in their routine.

So, what actually causes brassiness?

Hard Water

Let’s start with the biggest culprit—and the one I’m currently dealing with. Hard water is full of minerals like calcium, magnesium, and iron, which cling to your strands and alter the way your color looks. In darker hair, it can bring out coppery undertones. In lighter shades, it’s that yellow-y tinge. And in all cases, it dulls shine. (Tulum water, I love you—but you are not it.)

Sun Exposure

When the sun hits your hair, it can literally break down your color molecules. Especially if you're lightened or highlighted, your hair becomes more porous—meaning it soaks up more sun and shifts to warmer tones faster. UV + chlorine + salt? That’s the trifecta of brass.

Product + Oil Build-up

This one’s sneaky. Even if you’re not using “heavy” products, things like dry shampoo, serums, leave-ins, and your scalp’s own oils can build up over time. That film affects how your color reflects light—and it can make it look muddy, dull, or straight-up orange. (Especially in between washes… you know I had to say it.)

Chlorine + Salt Water

Salt dehydrates your hair, and chlorine is even worse. Both can rough up the cuticle, leading to uneven color and dullness. That green tint you sometimes see in blonde hair after a swim? That’s oxidation happening right on your head.

Using the Wrong Shampoo

Color correcting shampoo isn’t always the answer—and in some cases, it can make things worse. Overusing it can leave hair looking flat or tinted violet. Same goes for sulfate-heavy shampoos or silicone-laden formulas. These strip or coat your hair, which makes it harder for your true color to shine through.

How I Fix It (and What I Recommend to Clients)

If you’ve just looked in the mirror and realized your hair’s a little off—it’s okay. There are two main goals: remove what doesn’t belong (build-up, minerals, excess tone), and protect what does (your color, cuticle health, and shine).

Here’s what I do:

1. Clarify weekly—with a treatment, not just shampoo. A lot of people assume a clarifying shampoo is enough. But if you’re dealing with real build-up from hard water, sun, or product, you need something that goes deeper. I use our Clarifying Scalp Treatment once a week. It’s a pre-wash that melts through build-up and restores your scalp’s pH—without stripping or drying out your hair.

2. Follow with a clarifying shampoo—gently. After the treatment, I use our Clarifying Shampoo to rinse everything away. Unlike most clarifiers, it’s gentle enough for daily use, so you’re not left with that squeaky, straw-like feeling. But if you’re using another option, just make sure it’s color-safe and doesn’t strip your hair.

Two I like to recommend:

• Sam McKnight Light Cleanse Hair & Scalp Shampoo – A great silicone-free option that gently removes sebum, dirt, and build-up without causing irritation. It’s formulated with Aquaxyl (a sugar-derived complex) to support long-term scalp hydration and health—especially helpful if your scalp tends to feel tight or dry after clarifying.

• K18 Detox Shampoo – Another solid pick if you’re looking for a non-stripping, pH-optimized formula. It’s specifically designed to remove heavy metals like Nickel, Cadmium, and Iron—exactly the kind of build-up that leads to brassy tones over time.

The goal is to clear the brass-inducing stuff without compromising your hair health.

3. Add a showerhead filter.

This one’s a game-changer, especially if you live somewhere with hard water. A good shower filter removes chlorine and minerals before they even touch your hair. (I use one at home and always notice the difference when I travel without it.) Ours is currently sold out but I absolutely love the Canopy Showerheard Filter – plus they recently launched a handheld version I’ve been eyeing.

4. Protect your hair in the sun.

UV rays break down color molecules, especially in dyed or lifted hair. If I’m going to be outside, I throw on a hat , or try a physical barrier like a scarf or towel wrap post-swim. (Bonus: less sun damage = fewer split ends too.)

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My Shower Thoughts

Traveling between Mexico City and Tulum has been the best kind of reset. New energy, new routines—and a few new favorite spots I keep coming back to. If you’re planning a trip (or just bookmarking for the future), here’s what’s made my list so far:

Coffee

• Quentin in Mexico City makes one of the best flat whites I’ve had in a while.

• Long Time in Tulum is where I’ve been spending slow mornings.

• And Mera’s chili cacao? Unexpectedly perfect post-pilates.

Workouts

• Moon Pilates in CDMX is a must if you’re into reformer.

• And if you’re in Tulum, Kundalini at Holistika will leave you feeling completely reset.

Dinner

• Felix on the Park in Mexico City has that effortless indoor-outdoor energy and incredible food.

• In Tulum, Asian Bodega and Negro Huitlacoche are two spots I’d happily return to.

I’ll forever be on the hunt for the best croissant—but I’ll keep you posted.

Until next wash,

Helen