Mandelic Acid Applications

Dear Valerie: I’ve seen different brands promoting mandelic acid as a more effective treatment for acne than salicylic acid. Is mandelic acid that much superior or is this just marketing?  

—Buster Blemish

Dear Buster:

I’ve also seen some brands touting this and hearing this repeatedly really sticks in my craw! If you’re not familiar with mandelic acid, it’s an alpha hydroxy acid. Its structure essentially resembles glycolic acid, but with a terminal benzene ring. Purportedly, mandelic acid is much gentler than other AHAs like glycolic or lactic acids because of its larger size. As you may know, the larger a molecule’s size, the slower its ability to penetrate the outer layers of the skin, rendering it less irritating. Having personally used mandelic peels in my younger years, I can vouch for mandelic’s gentle caress from this aspect. Its pKA is around 3.4, which is on par with other alpha hydroxy acids. 

What vexes me is when brands compare its efficacy to a renowned, acne-treating molecule like salicylic acid. Why would anyone get the impression they’re on par with one another? Like-for-like?

One esthetician on social media quipped, “It’s because mandelic acid is also oil soluble, like salicylic acid!” 

Clearly, he never worked with mandelic acid in the lab (or researched its solubility data). In my personal experience, mandelic acid is much easier to incorporate into aqueous systems. Much like sugar dissolves in water, so does mandelic acid, to the tune of 15g/L. Salicylic acid’s water solubility in optimum conditions, in contrast, is about 2g/L. 

In terms of efficacy, there are a handful of studies comparing the efficacy of the two acids for the treatment of acne. One study¹ assessed improvement of acne in 50 patients, where 25 used a 20% salicylic peel, six times over 15 days. Another group used a 30% mandelic acid peel. While both groups had statistically significant improvement in acne lesion count, the salicylic acid group had more reduction.

Another study² found that a 30% salicylic acid peel and 45% mandelic acid peel performed on par for treating acne. Salicylic acid was better for non-inflammatory lesions, whereas mandelic acid was better for inflammatory lesions. Fewer side effects were observed with mandelic acid.

I found it interesting that another study evaluated 30% salicylic acid alone, versus 10% salicylic acid combined with 20% mandelic acid.³ By itself, salicylic acid reduced acne lesions more significantly than the combination peel. Both peels had side effects, including post-inflammatory hyperpigmentation (PIH).  The PIH was less pronounced in the combination peel.

There are many more papers with similar findings: salicylic acid is more effective, or on par, when compared to significantly higher quantities of mandelic acid. Given the fact that nearly double the quantity of mandelic acid is required to [sometimes] get this on-par effect, and they have different chemistries, they are not like-for-like materials!

There is one interesting aspect nearly all the papers noted; the side effects, including PIH, were less reported with mandelic acid. This makes sense, mandelic acid is less effective weight-for-weight. It operates via a different mechanism than salicylic acid. SA’s primary modus operandi is modulating sebum production and acting to treat specific inflammation pathways leading to acne.

I’m not sure why anyone would state that mandelic acid is superior to salicylic acid for treatment of acne. However, I’m altruistic, and I do like mandelic acid. I give mandelic acid credit, where credit is due.

As noted, mandelic acid has fewer side effects, which is especially beneficial for highly pigmented skin prone to PIH with acid use. PIH in higher Fitzpatrick skin populations is a real problem. Mandelic acid is a viable solution for those with acneic, pigmented skin. Salicylic acid is also generally deemed not appropriate for use by pregnant women, whereas mandelic acid does not have this restriction. Having recently been pregnant, I would have appreciated this fact—if I remembered in the shroud of pregnancy brain. 

In staying true to myself, and knowing my altruism can be limited, I would like to point out one final limitation. Mandelic acid is about 20 times the price of salicylic acid. So, there is that!

Valerie George
askvalerie@icloud.com

Valerie George is a cosmetic chemist, science communicator, educator, leader, and avid proponent of transparency in the beauty industry. She works on the latest research in hair color and hair care at her company, Simply Formulas, and is the co-host of The Beauty Brains podcast. You can find her on Instagram at @cosmetic_chemist or showcasing her favorite ingredients to small brands and home formulators at simply-ingredients.com