How do colour-changing lipsticks and blushes work? The science

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Have you seen colour-changing lipsticks and blushes online? A lot of these claim to “adjust” to your skin’s pH to give a personalised shade… but is it just a gimmick?

Here’s the chemistry behind these products.

Colour-changing ingredients

Red 27

Most colour-changing products – whether lipsticks or blushes – contain an ingredient called Red 27, also listed as CI 45410 (it’s also called Phloxine B when used in biology). This is a dye with a structure that changes depending on the conditions – one structure is colourless, while the second, more charged structure is a cool fuchsia pink.

The “magic” happens when it changes from the colourless structure to the pink structure. When there’s no water around it’s colourless, since water makes the charged pink structure more stable. It’s also colourless when there IS water around, but it’s below pH 2.5. When there’s water around AND it’s above pH 4.0, it’s pink. In between pH 2.5 and 4.0, there’s a mixture of both structures, so it goes from lighter to darker pink.

Colour-changing products have water-free formulas, so the Red 27 is colourless inside the tube. A lot of the time, the product is tinted to a different colour with other ingredients – green is common, since green changing to pink is pretty dramatic!

Your skin and lips have lots of water (water is evaporating through your skin all the time – it’s called transepidermal water loss, or TEWL). So after you apply it, the Red 27 reacts in the watery environment and turns pink, and you see the colour.

Here’s what Red 27 looks like in Bourjois Rose Exclusif gloss, swatched on a tissue – I swatched the bottom swatch first and let it react with moisture in the air, before adding the top swatch and taking a photo:

Is it a “custom” shade? Well, pH 2.5 is very low – your skin’s pH is somewhere around 5, and saliva is around 6.7. For comparison, lemon juice is around pH 2.3. So on anyone’s skin or lips, Red 27 is almost definitely going to be in its pink form – the only “custom” part is that it’s somewhat sheer, being a dye, so it can be buildable… just like any other sheer product.

This also explains why so many “personalised” lipsticks are just a cool pink shade – because Red 27 creates just the one pink shade. Red 27 is also used in a bunch of non-colour-changing products, since the dye stains the lips slightly for longer wearing colour.

Colour-changing products with Red 27:

Red 21

Red 21, also listed as CI 45380, is less common in colour-changing products. It’s also colourless when dry, but turns into a slightly warmer red colour when wet (in biology, it’s called Eosin Y – the “Y” stands for “Yellowish”). It starts turning pink above pH 0.0 and stops changing at pH 3.0, so again, there isn’t really any “custom” colour happening, aside from how much you apply. But compared to Red 27, it’s a bit more flattering for people with warmer skin.

It’s in some of Dior Addict Lip Glow Oils, but annoyingly the range includes both Red 21 and Red 27 in their “may contain” list. Here’s a swatch of Coral, which should be mostly Red 21:

Red 21 is also in Givenchy Rouge Interdit Vinyl Noir Revelateur (older version of this Givenchy balm), which I’ve swatched on a piece of tissue, then dripped water on the right side (I was a bit slow with the camera, so the left side was also starting to turn pink from moisture in the air):

Products with Red 21:

Side note: This is the same chemistry that happens with pH indicators – for example, litmus is red below pH 6 (acidic) and blue above pH 8 (alkaline or basic), and purple in the middle when it’s a blend of the two colours.

Products shown were provided as PR samples, which did not affect my opinion. This post also contains affiliate links – if you decide to click through and support Lab Muffin financially (at no extra cost to you), thank you! For more information, see Disclosure Policy.