Everything you need to know about silymarin in skincare
There’s an ingredient that's probbbaaabbbly not quite on your skincare radar yet - but we think it’s worth considering.
The ingredient is called Silymarin (sih-lee-mae-rin), and basically comes from the extract of milk thistle seeds. You'll find it on the ingredient list as "Silybum Marianum Fruit Extract", usually in a handful of clinical brands such as Skinceuticals, PCA Skin, and Dr. Dennis Gross…. And most recently our very own Mr. Reliable 2.0!
Silymarin is a potent antioxidant with anti-inflammatory properties. And wait! We know what you’re thinking – “hmm…that sounds like just about every other ‘skincare miracle; plant extract that’s out there”. But unlike thousands of touted plant extract elixirs, silymarin actually has tested topical benefits. It doesn’t sounds like a super high bar, but the reality is many plant extracts in skincare rely on data from in vitro tests (think petri dishes), animal models, or oral supplement tests that don’t necessarily translate directly to topical skincare efficacy. So the fact that silymarin has been tested topically and benched against existing skincare powerhouse actives such as hydroquinone makes our chemist senses tingle.
So let’s go through the data and see why silymarin has made its way into a few skincare formulas and happens to be hand-picked by us, the chemists, to include in our exciting Mr. Reliable Moisturizer 2.0!
How Did Milk Thistle End Up Skincare?
Milk thistle (Silybum marianum) has been used as traditional medicine for centuries across various cultures from the Greek to the Chinese. In traditional medicine, it has been used for a wide range of ailments… from liver diseases, gallbladder issues, to “melancholy”.
Given its long history of use, even modern medicine has taken an interest in milk thistle. Milk thistle has been through many tests. In fact, milk thistle was tested as an oral supplement to treat liver disease in a double blind, placebo-controlled, randomized study with 125 alcoholics. Though silymarin didn’t seem to help for liver disease in this particular study, it shows how much interest milk thistle has garnered through the years. So it’s not surprising to see that the buzz has caught on for potential topical skincare application too.
Is there any evidence for using Silymarin skincare? (in vitro and animal model)
Before anyone wants to spring the budget for a chemist-drool-worthy skincare clinical study, scientists typically start with petri dishes and mouse models to figure out if there’s any potential. Interestingly, there are over 30 studies out there that have tested silymarin in rodent models treating anything from burn wounds, sunburns, contact dermatitis, wound healing, and even fungal infection. What’s most interesting to us is the numerous tests linking silymarin to possibly functioning as an anti-inflammatory, antioxidant, and pigmentation fighter. But does that mean anything for human skin?
In terms of the mechanism on how silymarin would work on skin, there’s nothing conclusive but there seem to be a few theories:
- As an antioxidant/anti-inflammatory: This botanical has been linked to multiple modes including the inhibition of IL-1α as well as TNF-α, UVB, TPA, benzoyl peroxide-induced increase in myeloperoxidase activity, and others. Read: Inflammation is complicated and has a lot of markers. This is also why silymarin is linked to UV erythema claims.
- As a pigmentation fighter: Silymarin has been linked to activity as a tyrosinase inhibitor. As a refresher on what tyrosinase is, tyrosinase is an enzyme responsible for the cascade of melanin production in skin. For a refresher on hyperpigmentation and the different steps that your skincare can target, go here.
There’s actual human skincare clinicals behind a plant?
Time and time again, you’ll hear us rant about this on the Gram and sometimes the podcast too… but we always see ingredients that come with just a couple of petri dish studies and mayyybbee one mouse study get paraded around as the next fountain of youth. But the reality is, that really doesn’t tell us much about how the ingredient performs on our own skin.
Well well well, not only has silymarin been tested topically, we have comparative data against well-established skincare superstars such as hydroquinone *cue chemist jazz hands*
Silymarin vs. Hydroquinone
It turns out, silymarin has actually been tested against…the gold-standard hyperpigmentation fighter, hydroquinone… twice!
Clinical Study #1: A comparative clinical study of 112 female subjects that exhibited some degree of melasma tested 0.7% silymarin vs. 4% hydroquinone for 3 whole months and had a follow-up after the 6-month mark to monitor any melasma relapse. (Chemist note: this is an incredibly comprehensive clinical based on length of study, test size, and skin concern target) Subjects that used 0.7% silymarin used the cream twice a day vs. subjects that used 4% hydroquinone only used it once at night and were graded based on the MASI (Melasma Area and Severity Index) scoring system.
The results showed that at the 1 & 2 month mark, both treatments showed significant improvement, and 0.7% silymarin was found to perform on par with hydroquinone. It was only at the 3-month timepoint that hydroquinone performed significantly better than silymarin.
Clinical Study #2: A comparative study of 42 female subjects of various melasma severity was split into three groups that were to use 0.7% silymarin twice daily, 1.4% silymarin twice daily, and 4% hydroquinone once nightly for three months.
Clinical results showed that all three showed significant improvement in the MASI score after 3 months and all three (0.7% silymarin, 1.4% silymarin, and 4% hydroquinone) performed on par. We also want to emphasize that no difference was observed between 0.7% and 1.4% silymarin creams. (So more isn’t more in this case). Additionally, we should add that after 3 months of hydroquinone use, there were significantly more cases of adverse side effects (erythema, burning, scaling) vs. both silymarin groups where none were reported.
Silymarin vs. Glycolic acid peel
But wait! there’s even more. One study wanted to put silymarin through the wringer and wanted to test twice a day use of 1.4% silymarin vs. a 50% glycolic acid peel every two weeks vs. an intradermal injection of 5% tranexamic acid weekly for 12 weeks total. The study included 60 subjects with varying degrees of melasma and their skin was evaluated by expert graders and given a MASI score.
After 12 weeks of use, all three modes of treatments were found to show significant improvement. No side effects were reported for the group using silymarin, but adverse effects were reports for the other two groups.
So…exactly how does silymarin work in skin? Welp, skincare actives’ mechanism is probably one of the most mysterious subject to talk about. Silymarin most likely function as a powerful antioxidant and anti-inflammatory agent. There’s even a recent study that showed different components of milk thistle extract work to target tyrisonase, thereby slowing down melanogensis, which help explain why silymarin works to brighten skin. That said, exact skin pathway(s) can be quite complex.
Chemists’ Thoughts and Conclusions
You might be wondering… given how amazing silymarin sounds, why don’t we see it in more products? Sadly, like many lovely antioxidants, silymarin is actually REALLY unstable.
Let’s just say, it took us months of wrestling with this guy to get it to behave in formula and pretty much singlehandedly added 6 months to Mr. Reliable 2.0’s formulation timeline. We can’t even begin to tell you how many jars of sad, degraded, gunky creams we had on our desk at one point watching silymarin slowly decimate the formula. Eventually, it took a quirky blend of ingredients and an airless pump to reign this little guy in. Despite the long delays of launching Mr. Reliable 2.0, we're very proud that we're finally able to include this wonderful ingredient in our final formula!
- Silymarin is the extract of milk thistle that can be found in a few skincare products.
- Silymarin’s mechanism is not well understood however it has been linked to antioxidant, anti-inflammatory, and hyperpigmentation-fighting benefits.
- Surprisingly (in the most pleasant way possible!), there are a couple of solid clinicals showing that twice-a-day use of 0.7% silymarin performs on par with gold-standard actives such as 4% hydroquinone and glycolic acid.
- How to add silymarin to your routine: it depends on the format of the silymarin product! If you’d like to try out our Mr. Reliable 2.0, use this day and night after your hydrating serum
- What to lookout for in silymarin products: silymarin is notoriously unstable. If you decide to add a silymarin product to your routine, store in vampire mode (dark & cool) and keep an eye out for any drastic color changes!
Source for Curious: