Salicylic acid, a promising agent against psoriasis?

Due to a malfunction of the immune system, the psoriasis causes skin inflammation and a faster than average renewal of skin cells. These dead cells accumulate on the surface of the epidermis, resulting in the appearance of raised skin plaques that can be red and itchy.

Seemingly, thesalicylic acid would help both to reduce the size and improve the appearance of plaques. Four studies focusing on this BHA as a monotherapy for the treatment of psoriasis plaques and two studies on salicylic acid used in combination with other treatments (topical corticosteroids, anthralin, calcineurin inhibitors, etc.) for more severe cases of psoriasis have been analysed.

• Forty patients suffering from scalp psoriasis were treated in a 21-day double-blind study with an alcohol-based lotion containing either betamethasone-17,21-dipropionate at 0.05%, or salicylic acid at 2%, or a combination of 0.05% of betamethasone-17,21-dipropionate and 2% salicylic acid, or a placebo. The results showed that the addition of salicylic acid enhanced the activity of the betamethasone-17,21-dipropionate.

• A randomised controlled trial from 1986 reported successful treatment for moderate or severe scalp psoriasis using a 6% salicylic acid gel alone in 30 patients (10 inpatients and 20 outpatients). The inpatients were treated for three weeks with daily applications of 6% salicylic acid, which were then removed 24 hours later with a standard shampoo, while the outpatients were treated for six weeks with salicylic acid applied once a day and removed 12 hours later. Nine inpatients (90%) and thirteen outpatients (65%) found that the salicylic acid helped to reduce the size of the affected areas on the scalp.

• A 21-day multicentre, randomised clinical study revealed that the topical application of a combination of 0.1% mometasone furoate and 5% salicylic acid for 7 days, followed by 14 days of 0.1% mometasone furoate (n = 184), was more effective than monotherapy with 0.1% mometasone furoate (n = 176).

• In 2009, a small open pilot study involving 20 individuals revealed that those treated for three to six weeks with 6% salicylic acid as a monotherapy once a day experienced a significant "clearing" of their scalp.

• A 6% salicylic acid was assessed in a small open pilot study involving 10 individuals suffering from scalp psoriasis. Six out of the ten participants (60%) saw their psoriatic plaques completely or almost completely disappear after four weeks of monotherapy.

• In a randomised, double-blind comparative clinical trial conducted with 25 patients suffering from moderate chronic psoriasis, researchers evaluated the therapeutic efficacy of a 6% salicylic acid cream compared to a 20% AHA/PHA emollient. Both formulas resulted in a significant reduction in scaling at the end of the two-week treatment period.

• A small clinical study from 2022 involving 20 subjects aged over 18 with mild to moderate psoriasis (<10% of the body surface area) showed that an over-the-counter lipophilic aqueous gel containing turmeric and salicylic acid (3%), followed by a shea butter exfoliating moisturiser with salicylic acid, improved the appearance of psoriasis plaques after 12 weeks of once-daily use.

According to published results, it is suggested that salicylic acid alone can to some extent alleviate symptoms (itching, irritation, erythema, etc.) and soften scales to facilitate their removal, although the studies have some limitations (no control group, small number of participants, etc.). However, while it cannot target the root cause of psoriasis, salicylic acid can act as an initial and complementary therapy to other psoriasis treatments.

By what mechanism?

It is suggested that the main benefit of salicylic acid in the treatment of psoriasis lies in its ability to promote the removal of corneocytes through two possible pathways:

1. it reduces the adhesion and cohesion between dead cells by dissolving the intercellular cement (keratolytic effect);

2. it lowers the pH of the stratum corneum, which increases its hydration.

However, salicylic acid-based products only target the physical plaques and not the immune processes that lead to skin inflammation and hyperproliferation of skin cells. A systemic medication would be needed in addition to control the disease from an autoimmune perspective. Nevertheless, by detaching the links between the cells of the stratum corneum, it increases the penetration rate of other topical therapies for psoriasis and enhances their availability. Salicylic acid also has the ability to reduce inflammation, which helps to alleviate the itching and redness associated with psoriasis.

A 2015 review warns that salicylic acid is not an appropriate treatment for young children suffering from psoriasis due to a higher risk of systemic absorption and the negative reactions it presents. However, it appears to be safe in pregnant women with localised psoriasis.

Whether it's a keratolytic hair product for scalp psoriasis or perhaps a cream, lotion, gel or ointment for plaques located on the arms and legs, the recommended salicylic acid concentration for psoriasis is between 2% and 10%. However, the higher the concentration, the greater the risk of side effects and adverse reactions.

Precautions to be taken?

• Consult a dermatologist to determine the product and salicylic acid concentration that suits you best.

• Perform a patch test on a small area before committing to widespread use to ensure that you do not react negatively to the formula, as individuals with psoriasis already have sensitive skin.

• Begin by applying a small amount of the product to a single psoriasis area. Try this method for several days to see how the body responds.

• Limit the application of salicylic acid to areas affected by psoriatic lesions. No more than 20% of the body surface should be involved, as the skin can absorb salicylic acid. If you apply it over too large an area of the body, this can cause an overdose and lead to potential chronic or acute systemic poisoning (salicylism, vomiting, dizziness, nausea, severe headaches, etc.). Similarly, avoid using it to treat widespread psoriasis.

• Opt for formulas containing moisturising ingredients (hyaluronic acid, glycerine, ceramides, etc.) due to the drying and irritating nature of salicylic acid, in addition to helping improve the skin's barrier function.

• Medicated shampoos containing salicylic acid, whether available over-the-counter or on prescription, should only be used for a short period of time.

• The use of salicylic acid should be avoided on the genital organs, mucous membranes and eyes.

• Do not apply salicylic acid before UVB phototherapy, as at a concentration >0.1%, it has photoprotective effects and thus blocks ultraviolet light.

• Do not use topical salicylic acid concurrently with calcipotriol, as it may reduce its effectiveness.

This will not replace medications prescribed by a dermatologist, but it can significantly alleviate itching and soften scaly skin.

• KAVALEC E. C. & al. Effect of salicylic acid on the activity of betamethasone-17,21-dipropionate in the treatment of erythematous squamous dermatoses. Journal of International Medical Research (1983).

• HUNTER J. A. & al. Salicylic acid gel for scalp psoriasis. Clinical and Experimental Dermatology (1986).

• LEBWOHL M. The role of salicylic acid in the treatment of psoriasis. International Journal of Dermatology (1999).

• SALAVASTRU C. M. & al. Mometasone furoate 0.1% and salicylic acid 5% vs. mometasone furoate 0.1% as sequential local therapy in psoriasis vulgaris. Journal of the European Academy of Dermatology & Venereology (2009).

• KIRCIK L. Salicylic Acid 6% in an ammonium lactate emollient foam vehicle in the treatment of mild-to-moderate scalp psoriasis. Journal of Drugs in Dermatology (2011).

• FELDMAN S. R. & al. A double-blind, randomized clinical trial of 20% alpha/poly hydroxy acid cream to reduce scaling of lesions associated with moderate, chronic plaque psoriasis. Journal of Drugs in Dermatology (2013).

• AUGUSTIN M. & al. Keratolytics and emollients and their role in the therapy of psoriasis: a systematic review. Dermatology and Therapy (2015).

• GAUTAM M. M. & al. Topical therapies in psoriasis. Indian Dermatology Online Journal (2017).

• DRAELOS Z. D. The efficacy and tolerability of turmeric and salicylic acid in psoriasis treatment. Psoriasis (2022).