Investigation: Salicylic Acid and Willow Bark Extract?
Posted on April 26 2017
As an ingredient nerd and skin therapist working with clients, you learn that salicylic acid is a top notch ingredient for acne and breakout-prone skin. Salicylic acid penetrates into the pores, seeking out oil (sebum) and decreasing its secretion. Salicylic acid also exfoliates dead skin cells and has anti-inflammatory attributes. (Fun Fact: Although salicylic acid is generally referred to as a beta hydroxy acid, it actually is a phenolic aromatic acid. Likely, it was labeled as a beta hydroxy acid because it is a lipid-soluble agent, in contrast with the alpha hydroxy acids, and because "beta hydroxy acid" peels were introduced in the market in order to exploit the benefit of the popularity of alpha-hydroxy acids.)
Salicylic Acid is a "Drug"
As an ingredient nerd (and erstwhile lawyer) working to formulate products, you learn that salicylic acid is considered a drug by the FDA. In products containing salicylic acid concentrations of 0.5% to 2%, it is considered an active ingredient, an "over the counter" drug, meaning you can buy the finished product straight from the shelves. (Take a look at the back of an "acne product" -- the salicylic acid will be listed at the top of the ingredient panel, as an "active ingredient" and the percentage will be listed.) In products containing a concentration over 2%, a prescription and a visit to the pharmacy is required. In either case, if a company wants to sell products containing salicylic acid, its facility and the product must be registered with the the US Food and Drug Administration and the facility must operate under Current Good Manufacturing Practice guidelines.
While large companies can afford (with both time and money) to comply with the FDA drug regulations, the rest of us cannot. Rather, we must look for salicylic acid alternatives. This is difficult, however, because salicylic acid is the only beta hydroxy acid that is used in dermatological practice.
Is Willow Bark Extract a Salicylic Acid Substitute?
Many companies turn to willow bark extract to fill the beta hydroxy acid role. However, willow bark is a source of a lot of confusion in this regard.
The confusion happens because willow bark extract contains anti-inflammatory salicin, a type of salicylate. When orally ingested, salicin is converted by the digestive process into salicylic acid. In a laboratory setting, salicin can be chemically oxidized to yield salicylic acid. (Fun Fact: Salicylic acid is the precursor to aspirin.)
In other words, willow bark is a SOURCE of salicylates (specifically, salicin), which may then be chemically converted into salicylic acid, but is NOT salicylic acid itself. Accordingly, despite the statements of many cosmetic companies and ingredient producers, white willow bark extract is not a true salicylic acid substitute. Rather, it is a "related substance," at most ideal for reducing inflammation and associated redness, with the bonus of possibly having an antimicrobial effect, but it is not going to be the oil-seeking, oil-decreasing, acne-busting superstar that is salicylic acid.
You may see a label or website state that willow bark extract (or any other number of ingredients) is a "natural source of salicylic acid." By the magic of marketing, they're not exactly wrong, in the sense that salicylic acid can be "sourced" from willow bark extract, but this leads to the unsuspecting consumer's incorrect conclusion that the willow bark extract in the product is the equivalent of salicylic acid.
At present, there is no proper, "natural" alternative for topical use salicylic acid. If you want the results of the real thing, stick with the big brand names in the big shop aisles.
Pregnancy, Salicylic Acid, and Willow Bark Extract
Studies of willow bark extract use during pregnancy has been limited to oral use. In that regard, European Medicines Agency concluded that oral use of the extract is contraindicated in the third trimester of pregnancy and not recommended during the first and second trimester and while breastfeeding. It is important to restate at this point that in oral use of willow bark extract, the digestive process converts the salicin into salicylic acid.
Similarly, oral use of low-dose acetylsalicylic acid (aka: aspirin) during pregnancy has been a topic of a large number of studies. These studies have found that there was no increase in the baseline risk of adverse events, such as major malformations, preterm birth, or low birth weight. No studies have been conducted in pregnancy on topical use of saliclylic acid. As such a relatively small proportion is absorbed through the skin, however, it is unlikely to pose any risk to a developing baby.
Sources and Further Reading
Maroon, J. Bost, J. Maroon, A. Natural anti-inflammatory agents for pain relief. Surg Neurol Int. 2010; 1: 80.
Decker, A. Graber, E. Over-the-counter Acne Treatments: A Review. J Clin Aesthet Dermatol. 2012 May; 5(5): 32–40.
Arif, T. Salicylic Acid as a Peeling Agent: A Comprehensive Review. Clin Cosmet Investig Dermatol. 2015; 8: 455–461.
Mahdi, J. Medicinal Potential of Willow: A Chemical Perspective of Aspirin Discovery. Journal of Saudi Chemical Society. 2010 Jul; 317-322.
Ishikado, A. Sono, Y. Matsumoto, M. Robida-Stubbs, S. Okuno, A. Goto, M. King, G. Blackwell, K. Makinoa, T. Willow bark extract increases antioxidant enzymes and reduces oxidative stress through activation of Nrf2 in vascular endothelial cells and Caenorhabditis elegans. Free Radic Biol Med. 2013 Dec; 65: 10.1016
Bozzo, P. Chua-Gocheco, A. Einarson, A. Safety of skin care products during pregnancy. Can Fam Physician. 2011 Jun; 57(6): 665–667.
EMEA 2009. European Medicines Agency. Community Monograph. London (GB): EMEA Committee on Herbal Medicinal Products (HMPC), 14 January 2009.
Kennedy, D.A. Lupattelli, A. Koren, G. Nordeng, H. Safety classification of herbal medicines used in pregnancy in a multinational study. BMC Complement Altern Med. 2016; 16: 102.