What Can Be Used To Replace Salicylic Acid?

Salicylic acid is a popular active ingredient that has long been used to treat a variety of skin conditions (acne, hyperkeratosis, etc.). Thus, there are several preparations on the market containing salicylic acid, for the care of skin and hair. It is found in small doses due to its well-documented antibacterial and keratolytic properties.

Although it has few side effects at concentrations of 3% or less and is neither photosensitizing nor phototoxic, a scientific study by a team of Danish researchers has indicated an endocrine effect of the active ingredient. The study had shown that its use lowers testosterone levels in addition to having an antiandrogenic and spermatogenic effect.

However, there is limited data on the endocrine-disrupting potential of salicylic acid. Moreover, the doubts surrounding it come from studies conducted with molecules of the same family (salicylates and acetylsalicylic acid, i.e. aspirin), in addition to being conducted in vitro. The European Commission has therefore launched a call for data to clarify this point. The safety of the use of salicylic acid in cosmetic products has been evaluated by European and U.S. experts and found to be safe at concentrations approved for cosmetics in a statement published in September 2018.

Thus, these allegations require further investigation. Nevertheless, these new allegations against salicylic acid have led to some concern about its use in skin and hair care. Find out about a possible alternative: β-lipohydroxy acid.

What Is β-Lipohydroxy Acid (LHA)?

With the chemical formula C15H20O4, β-lipohydroxy acid (LHA), also known as 2-hydroxy-5-octanoyl benzoic acid, is a lipophilic derivative of salicylic acid developed by L'Oréal Recherche in the late 1980s.

Compared to salicylic acid, an acyl fatty chain with eight carbon atoms was added to the fifth carbon atom of the benzene ring of salicylic acid. The addition of this fatty group makes LHA more lipophilic than its relative, which may explain its different properties.

First of all, it has a much lower skin penetration, as shown by several in vitro and in vivo studies, which is also due to its high molecular weight (MG = 264.3 g/mol). In fact, LHA remains stored in the uppermost layers of the stratum corneum. Moreover, the lipophilic nature of LHA and its relatively slow penetration into the skin give it an exfoliating effect that is effective even at low concentrations (< 10%).

LHA appears to possess antimicrobial, anti-inflammatory, antioxidant, anticomedogenic, and exfoliative properties. Thus, chronic use of a skin care regimen containing LHA improves the appearance and texture of the skin. It also improves the appearance in terms of clarity. Let's take a closer look at these properties.

What Are the Properties of LHA on the Skin?

• Antibacterial and anti-inflammatory properties:

LHA has the potential to significantly reduce the intensity of inflammatory symptoms. In addition, it is said to have an antibacterial effect by having the ability to reduce follicular bacterial load.

• Antioxidant activity:

In vivo and in vitro studies have shown a protective effect of LHA. Daily use of LHA has been shown to increase the skin's resistance to UV-induced damage with its ability to neutralize free radicals. Specifically, LHA can inactivate singlet oxygen (¹O₂) without reacting with it and "turn off" the superoxide anion (O2-). It also reacts with hydroxyl radicals to produce 2,5-dihydroxybenzoic acid, which is an excellent superoxide anion scavenger.

• Anti-dandruff action:

Dandruff is associated with colonization of the scalp by yeasts of the species Malassezia, particularly M. ovalis (Pityrosporum ovale). These microorganisms require an exogenous source of fatty acids to proliferate. Therefore, areas of the head that have higher sebum production are particularly favored. In vitro experiments show that LHA has similar antimicrobial activity against M. ovalis as piroctone-olamine, a commonly used anti-dandruff agent. Its antifungal and exfoliating properties should also prove useful in combating dandruff.

• Comedolytic activity:

LHA has also been shown to be effective in preventing and treating mild to moderate acne. Studies have shown that after only four weeks of treatment, an LHA formulation is able to remove the horny plugs (comedones) that have accumulated in the pores of acne patients' faces. The size and number of comedone lesions (closed comedones, open comedones) and inflammatory lesions (papules, pustules) decreased significantly over time due to loosening of intercorneocytic binding and bacterial adhesion within follicular openings. Due to its lipophilic nature, LHA has a distinct affinity for the sebum-clogged pores of people with acne. It can more easily enter sebaceous gland-rich skin, improving or alleviating such skin conditions. In addition, according to another study, this ingredient is also interesting in preventing acne recurrence in summer.

• Illuminating effect:

With its keratolytic action, LHA also helps reduce the visibility of brown spots by promoting the distribution of melanosomes in the epidermal layers, resulting in a more even skin tone.

• Exfoliating activity:

LHA is primarily a potent keratolytic agent due to its ability to divide the desmosomes that connect corneocytes in the stratum corneum. It then allows desquamation to release excess corneocytes under hyperkeratotic conditions. However, unlike salicylic acid, LHA does not penetrate as deeply. Therefore, it is more likely to break up the more superficial corneodesmosomes. In addition, the slow penetration of LHA, in particular, results in cell-by-cell individual exfoliation that mimics physiological desquamation rather than the more extensive exfoliation that occurs with the use of salicylic acid and other AHAs. Thanks to this property, it thus causes a reduction in the thickness of the stratum corneum and an increase in softness as short-term effects on the skin.

An essential part of the exfoliation process is the stimulation of epidermal renewal with increased cell division. Several studies have shown that topical application of a 2% LHA formulation increased the thickness of all layers of the epidermis. One hypothesis is that the mechanism by which LHA increases cell renewal is due to a signal from the release of lamellar lipids during enhanced desquamation or mechanical forces from exfoliation that could stimulate physiological responses. It has also been shown that LHA stimulated collagen formation and induced dermal thickening in a model of human reconstructed skin. Therefore, LHA has stimulatory effects on dermal keratinocytes and dendrocytes that mimic those of retinoic acid to some extent.

What Can Be Said About the Tolerability of β-Lipohydroxy Acid (LHA)?

LHA has a very good safety profile compared to glycolic acid or retinoic acid, with good tolerability and a lower incidence of irritation. However, photodegradation of LHA may occur, limiting its effectiveness. Therefore, it should be applied in the evening or a suitable sunscreen should be applied to protect LHA from the sun's UV rays and prevent its degradation.

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