What are the dangers of arbutin acid?

Before analysing its safety profile, let us recall why arbutin has become a benchmark active ingredient. Mainly used for its depigmenting action, it works by inhibiting tyrosinase, the enzyme responsible for the production of melanin. Beyond this ability to reduce pigment spots, studies also attribute antioxidant and anti-inflammatory properties to arbutin, making it a versatile active ingredient for promoting radiance and an even complexion.

However, the chemical structure of alpha-arbutin is at the heart of toxicological concerns.

Indeed, arbutin is a glucoside of hydroquinone. This means that it is composed of a hydroquinone molecule to which a glucose group is attached. While arbutin is permitted in cosmetics, hydroquinone, on the other hand, has been strictly banned in Europe since 2001, except for regulated medical use, due to its toxicity and serious side effects. Hydroquinone is particularly suspected of being carcinogenic and mutagenic. The potential danger of arbutin therefore lies in its retro-conversion: the breaking of the chemical bond between glucose and hydroquinone would release the latter onto the skin.

However, the stability of arbutin in a cosmetic product is not absolute.

Several environmental factors can trigger its hydrolysis, and thus the release of hydroquinone, such as heat, pH – more specifically an acidic pH – and exposure to UV radiation. One study in particular examined the stability of arbutin under various stress conditions. The researchers tested 21 products using high‑performance liquid chromatography (HPLC). One of the creams, labelled as containing 1.61% arbutin, already contained 0.12% free hydroquinone at baseline. Moreover, intensive thermal degradation tests (up to 120°C for 6 hours) confirmed a release of hydroquinone from pure arbutin.

However, these results should be interpreted with caution: the temperature of 120°C used to induce this decomposition is considered extreme.

For comparison, the stability and accelerated ageing tests carried out by the cosmetics industry, which involve subjecting a product to high temperatures for several weeks in order to simulate several years of storage, generally do not exceed 45°C to 50°C. Although the risk of thermal conversion therefore appears limited under normal conditions of use, caution is still required with regard to prolonged UV exposure, which can break down arbutin acid into hydroquinone and p-benzoquinone, an oxidising agent.

The risk of transformation does not end with the vial’s stability; it continues during application.

Indeed, our skin hosts billions of micro-organisms that possess their own enzymes. Common bacteria of the cutaneous flora, such as Staphylococcus epidermidis or Staphylococcus aureus, are capable of metabolising arbutin. By secreting certain enzymes, they can break the glucose–hydroquinone bond directly at the surface of the epidermis. While this conversion can theoretically increase the lightening efficacy, since hydroquinone is more potent, it also raises a genuine concern about the actual and uncontrolled exposure of the body to this molecule, which is banned by cosmetic regulations.

In summary, although arbutin acid is a legal alternative to hydroquinone, its tendency to transform calls for caution and continued research.

In addition to its potential conversion into hydroquinone, arbutin acid on the skin may trigger undesirable reactions. Although these remain relatively uncommon, various clinical reports mention redness, burning sensations and tingling associated with the topical application of arbutin.

A Japanese clinical report has notably detailed the case of a 60‑year‑old female patient who developed a facial oedematous erythema with associated itching after using a skin‑lightening cream. Patch tests clearly confirmed an allergic reaction to arbutin, which persisted even at very low concentrations, around 0.3%, while the other components of the product had no effect. Although such allergic cases are regarded as fairly rare in the scientific literature, they serve as a reminder that arbutin is a potentially sensitising substance.

The warning signals related to arbutin acid are not subsiding. Although toxicological studies often focus on ingestion, their findings cannot be completely disregarded in cosmetology. The precautionary principle suggests that substances which are toxic when taken orally could, through prolonged cutaneous absorption, present similar risks. Arbutin in particular raises questions about hepatic and cerebral toxicity.

Studies conducted on rats have shown that at very high doses (2,000 mg/kg), alpha-arbutin can cause an increase in liver enzymes and cerebral inflammation characterised by necrosis of the epithelial cells of the cortex. Although these doses are far higher than those used in cosmetic applications, they reveal the cytotoxic potential of the molecule.

Furthermore, concerns about arbutin also extend to the hormonal sphere. An in vitro study conducted on Leydig cells, the testicular cells responsible for testosterone production, showed that exposure to arbutin led to a significant inhibition of androgen secretion. At a concentration of 50 μM, the active compound was even able to block the stimulatory effects of luteinising hormone, which is essential for reproductive function. Analyses showed that arbutin acts by downregulating the expression of several genes involved in hormone synthesis, such as Lhcgr, Hsd3b1, Cyp17a1 and Srd5a1.

Although these data are derived from cell models rather than from applications to the skin, they highlight the need for continued caution.

In light of these data, the Scientific Committee on Consumer Safety (SCCS) has established strict thresholds to limit systemic exposure to arbutin acid. Since 2015, the recommendation has been to not exceed 2% alpha-arbutin in facial skincare products and 0.5% in body lotions. These limits are intended to ensure that, even in the event of partial conversion into hydroquinone on the skin, the amount absorbed remains below critical toxicity thresholds. However, the question of cumulative effects with regular use over several years remains a matter of concern and ongoing monitoring in dermatological research.

Even though arbutin acid is effective in managing hyperpigmentation, its safety profile calls for constant vigilance. Between its chemical instability and the warning signals emerging from toxicological research, its use cannot be considered entirely harmless.

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