By Kristina Vile, M.Sc. Molecular Biomedicin, AllergyCertified

What is it?

Salicylic Acid is an organic acid sometimes called a Beta-Hydroxy-Acid (BHA). It is probably best known as a compound that is chemically similar but not identical to the active component of aspirin (acetylsalicylic acid). salicylic acid occurs naturally in the bark of the willow tree, Salix alba.

Salicylic acid has many functions in cosmetic formulations and is used as a denaturant, a hair and skin conditioning agent, an exfoliant, an anti-acne cleansing agent, an anti-dandruff agent and a product preservative.

Similar to other hydroxy acids, salicylic acid is a key ingredient in many skincareproducts for the treatment of seborrhoeic dermatitis, acne, psoriasis, calluses, corns, keratosis pilaris, acanthosis nigricans, ichthyosis and warts.

What is the problem?

As a topical agent, salicylic acid is capable of penetrating and breaking down fats and lipids, causing moderate chemical burns of the skin at high concentrations.

Concentration limits are set at 2% for topical preparations expected to be left on the skin and 3% for those expected to be washed off, such as acne cleansers or shampoo; up to a 6% concentration can be used under prescription.

As a preservative salicylic acid is allowed in concentrations up to 0.5%. The difference between the allowed 2% in leave on and the 0.5% as preservative is based on the specific use of the products.

Salicylic acid as an active ingredient is used locally e.g. in a foot cream versus use as a preservative in a body lotion where the exposure area is much bigger. 

In a report published from Danish Center for Endocrine Disrupters (CeHoS), in September 2018, CeHoS together with DTU looked at suspected and potential endocrine disruptors form various preexisting lists and made an evaluation of the scientific evidence compared to the criteria for classifying endocrine disrupters.

Among the evaluated chemicals salicylic acid was evaluated as an endocrine disruptor.

What do the experts say?

In the report from Danish Center for Endocrine Disrupters (CeHoS) salicylic acid was evaluated as endocrine disrupting with strong evidence from the literature.
Most studies reviewed in the report is based on oral intake of salicylic acid or derivatives such as acetylsalicylic acid. Studies based on dermal application is lacking, but it has been shown that up to 60% of salicylic acid will be absorbed through the skin.

The Scientific Committee on Consumer Safety (SCCS) made a report on salicylic acid published in December 2018. The report considers Salicylic acid safe when used as a preservative in concentrations up to 0.5%. When used for other purposes salicylic acid is considered safe up to 3.0% in rinse off products and up to 2.0% in other products.
However, in body lotion, eye shadow, mascara, eyeliner, lipstick and roll on deodorant applications, salicylic acid is considered safe up to 0.5% only as preservative. The SCCS report dose not include safety of oral products or sprayable products.

The SCCS opinion on fertility and reproduction is based on data from 2016 and concludes that salicylic acid should not be classified as a reproductive toxicant for the fertility endpoints. Also, the opinion on developmental toxicity is based on data from 2016 and says that salicylic acid is a developmental toxicant.
Harmonised classification of salicylic acid was recently published in Regulation 2018/1480 where it is classified as Repr. 2 (H361d Suspected of damaging the unborn child). Salicylic acid is not to be used for children under 3 years.

The SCCS opinion on endocrine disruption is not based on the newly published report from CeHoS, but the report is mentioned with a comment that in the future the perception of salicylic acids endocrine disrupting properties may change:

“In a newly published report from the Danish Centre on Endocrine Disrupters researchers from the National Food Institute, Technical University of Denmark, and the University of Southern Denmark have evaluated that there is solid scientific evidence that salicylic acid is an endocrine disruptor. In this report different derivatives of Salicylic acid have been used, e.g. acetylsalicylic acid (Aspirin), sodium salicylate and methyl salicylate. SCCS is also aware that in the framework of the Biocide regulation, specific tests are currently on-going to assess whether salicylic acid has endocrine disrupting properties. Depending on the outcome of these tests, the potential endocrine disrupting properties of salicylic acid in cosmetics may need to be considered.”

The Cosmetic Ingredient Review (CIR) Expert Panel (Panel) reviewed the safety of Salicylic Acid and concluded this safe within the limitations to concentrations mentioned. They calculate a Margin of Safety (MOS) value based on the concern over the potential reproductive toxicity of salicylic acid. If a MOS value is over 100 it is considered safe.
The calculated MOS value of rinse off products is 370 and 432 and for leave on the MOS is 177. This indicates that based on the potential reproductive toxicity data salicylic acid in the concentrations used in cosmetics is safe.

CIR did not include the report fromCeHoS with evidence for endocrine disrupting properties of salicylic acid.

Allergy certified

Salicylic acid does not cause skin allergy and was previously accepted in AllergyCertified products.

Both the SCCS and CIR report are important tools in our assessment of ingredients used in the products we certify. In this case however, we se a delay in evaluation of the new information from the report form CeHoS with evidence for endocrine disrupting properties of salicylic acid. The SCCS and CIR report are both dated after the CeHoS report and this may confuse people to think that they included this new information when the fact is that they did not.

When we receive information that salicylic acid classifies as an endocrine disruptor according to the new criteria, we can no longer approve this in certified products. This was informed to our clients in November 2018.

We encourage studies looking at the risk factor for exposure through the skin and studies to find a possible safe level regarding this exposure for the endocrine disrupting properties. 

Literature:

• Scientific Committee on Consumer Safety (SCCS) OPINION ON salicylic acid, SCCS, December 2018
• Amended Safety Assessment of Salicylic Acid and Salicylates as Used in Cosmetics, CIR, January 2019
• List of Endocrine Disrupting Chemicals, Final report, December 21th, 2017 (Some mainly editorial chances were made in September 2018), Danish Center for Endocrine Disrupters (CeHoS), September 2018