The Olaplex No.4P Purple Shampoo is a bestseller—here's our honest opinion and guide to how it works before you buy

There's a lot of hype around this brand's products over on TikTok, and one of the newer additions to the lineup, Olaplex No.4P Blonde Enhancer Toning Shampoo, is no exception.

For the uninitiated, the best Olaplex products rose to fame almost overnight thanks to the two initial in-salon treatments—perfect for those who frequently bleach or dye their hair. The first is mixed into your hair color, the second is the equivalent of a professional-strength deep conditioning mask and is applied at the backwash. 

Both are scientifically proven to prevent the disulfide bonds in your hair from breaking during the coloring process by effectively ‘gluing’ them together. Olaplex also prevents any protein-destroying molecules from ravaging your strands by stepping in before they have the chance to wreak havoc. Hello, switching up your hair color while maintaining healthy strands.

Since the first two in-salon products took the beauty industry by storm, the line has branched out to a whopping 12. Each has a different purpose, but are all powered by the same hero ingredient as the salon treatments, albeit at lower concentrations. While the visual improvements Olaplex achieves are a welcome effect, this patented molecule actually improves the hair's structure—rather than just papering over the cracks—a claim that most haircare brands simply couldn't make. This newbie is certainly an appealing premise; slather this sulfate-free shampoo onto highlighted, gray, or natural blonde hair to cleanse, tone, and repair in one fell swoop.

But does it live up to the same hype bestowed upon the cult No.3 treatment, or its newer counterpart the No.9 Serum? Given that my highlighted blonde hair is prone to losing that cool tone after a few washes, I wanted to put it through its paces to see how the results fare. 

Meet the tester

Meet the tester

Fiona Embleton

Up until the age of 16, I was like a beacon for lost Scandinavian tourists on the subway, who’d launch into a friendly Swedish welcome having clocked my natural platinum strands. But with each subsequent birthday my hair became a little darker and duller, eventually straying into "mousy" territory—neither blonde nor brown, but some dishwater hue in between. I missed my natural shade and positively hated having a hair color named after a rodent.

Ever since then, I’ve religiously highlighted my hair every three months. Nothing beats the euphoria of stepping out of a salon root-free, but the sentiment is short-lived if your apartment is in a hard-water area (like mine). Minerals and metals penetrate blonde hair, which tends to be more porous, causing warm tones to creep in.

For full transparency, I’m already a big fan of Olaplex. The in-salon treatments have done the unthinkable and resuscitated my bleached strands, while the Olaplex No.3 Hair Protector has been a part of my Sunday night regime ever since I can remember. So I was naturally intrigued that the brand had ventured into color-correcting haircare and couldn't wait to try the No4.P Shampoo.

A beauty editor's honest review of Olaplex No.4P Blonde Enhancer Toning Shampoo

Ingredients—What's in the Olaplex No.4P Purple Shampoo?

As for the newer shampoo, Olaplex No.4P Blonde Enhancer Toning Shampoo is a customizable purple formula with highly concentrated pigments—so you can dial up the toning depending on how brassy your hair is. To quickly recap color theory and how the best purple shampoos work, purple sits across from yellow on the color wheel, which is why this type of shampoo is so effective at neutralizing brassy tones. 

According to clinical trials, hair looks three times brighter after just one use of the Olaplex No.4P compared to other top purple shampoos in the market. But what really sets this particular purple shampoo apart from competitors is that it also contains Olaplex’s patented molecule, bis-aminopropyl diglycol dimaleate. Put simply, this high-tech molecule rebuilds the broken bonds in the hair that result from heat styling, chemical treatments, and (this is a key one in blonde hair) bleaching. You can read more about its benefits in our guide on using Olaplex as a treatment. 

Admittedly, the levels of this particular ingredient aren’t as high in this formula as in the salon-only treatments, No.1 Bond Multiplier and No.2 Bond Perfector. But every little helps when you consider that the oxygen molecules in peroxide attach themselves to bonds and deplete the hair's protein, leaving it brittle. What's more, like all Olaplex products, No. 4P Shampoo is both vegan and cruelty-free, as well as containing no formaldehyde, sulfates, parabens, phosphates, or phthalates. 

Application—How to use the Olaplex No.4P Purple Shampoo

To achieve optimum results from this brightening shampoo, you should follow the instructions on the bottle. It’s also important to do a patch test inside your elbow or behind your ear and wait 48 hours to ensure there's no irritation.

• Step 1 (optional): Pre-wash with No.4 bond Maintenance Shampoo to remove product build-up.
• Step 2: Apply No. 4P Blonde Enhancer Toning Shampoo to wet hair. Lather and leave to process for one to three minutes. For more intense toning, leave on hair for up to five minutes. Use two to three times a week or as often as needed.
• Step 3: Rinse fully. Follow with No.5 Bond Maintenance Conditioner, or No.8 Bond Intense Moisture Mask for extra hydration.

The verdict—Is Olaplex No.4P Purple Shampoo worth it?

Like most bottle blondes, I’ve tried my fair share of purple shampoos to brighten my highlights between salon visits. The trouble is, while those deep amethyst-hued shampoos certainly nix brassiness, they also suck the moisture from my strands, leaving them the same shade and texture as straw. Daily lilac shampoos, on the other hand, are too watered down, making very little difference to the overall result. However, this wasn't the case with Olaplex's toning offering. 

The first thing to say about Olaplex No.4P is that my hair looked and felt salon-fresh after using it. The tone is customizable, so on a new dye job I was only leaving it on for a maximum of three minutes once a week. After six weeks, I upped the toning time to five minutes, twice a week. It’s also sulfate-free, so the formula isn’t harsh on strands or on the scalp, which is important given what your roots go through in the colorist’s chair. Either way, my hair never felt parched and, crucially, I was putting goodness back into strands post-color courtesy of Olaplex’s infamous bond-repairing molecule—it would also work well in an Olaplex routine for curly hair that's been bleached blonde and needs cooling. 

I also love that this is a shampoo you can just slot into your regular hair care routine. You don’t have to buy a separate conditioner to create a de-brassing ‘system’; you just follow up with your usual No.5 Bond Maintenance Conditioner. Of course, you could use another conditioner if you wish, but I find products from the same brand tend to work in synergy and with Olaplex this is all the more important given the special molecule all the products share. For me, the luminous shine and multi-dimensional tones to my hair are testament to that.

The cherry on top? The purple shade doesn’t stain your hands or your shower curtain. For this bottle blonde, Olaplex No.4P is a no-brainer.