Which active ingredients should be used for oily skin (+)?

Oily skin (+) is a common dermatological concern. Although the sebaceous glands play an essential role in the skin’s barrier function by conferring water-repellent properties to the stratum corneum, they are also responsible for excessive sebum production, resulting in an undesirable shiny appearance and enlarged pores. Numerous factors have been proposed to contribute to the pathogenesis of oily skin, and active ingredients have been identified to regulate this hyperseborrhoea through various mechanisms of action.

Azelaic acid for long-lasting sebum regulation.

L'azelaic acid would be one of the substances that regulate the function of the sebaceous glands. As demonstrated by a study conducted by ERKIERT-POLGUJ A. and colleagues on 27 women aged between 19 and 25 years, the topical application of a series of six treatments with a 20% azelaic acid solution resulted in a significant reduction in sebum secretion levels. On the forehead, the mean sebum amount was 195.5 before treatment and 162.7 after the six treatments; for the cheek, the mean values were 175.3 before treatment versus 141.3 after the sixth application of azelaic acid.

The mechanism of action underpinning this sebostatic effect is the inhibition of 5α-reductase, an enzyme that leads to enhanced androgenic activity accompanied by excessive sebum production (hyperseborrhoea). It has been proposed that this inhibition results from azelaic acid competitively occupying the NADPH binding site of 5α-reductase. Consequently, azelaic acid appears to represent a potential therapeutic agent for oily skin.

Bakuchiol, theplant-based analogue of retinol targeting sebum overproduction.

Beyond its anti-ageing and antioxidant properties, studies in vitro have shown that the bakuchiol is capable of inhibiting three key pathways involved in acne pathogenesis, including the reduction of sebaceous gland activity. According to an in vivo, its sebum-regulating mechanism is attributed to the downregulation of 5-α-reductase expression, the enzyme strongly involved in sebum overproduction. At a concentration of 10 µg/mL, bakuchiol showed an approximately 40% reduction in the expression of this enzyme, an effect comparable to that of retinoic acid.

In a series of five clinical trials, one assessed the efficacy of a night-time serum containing 0.5% bakuchiol, combined with melatonin and ascorbyl tetraisopalmitate, in 31 participants with oily skin. After 28 days of application, sebum secretion was reduced by 18.2%, demonstrating that the product is suitable for oily skin.

However, it is difficult to attribute the reduction in sebum solely to bakuchiol, given the presence of other potentially synergistic active compounds, as well as certain methodological limitations such as the absence of a placebo group. Moreover, clinical data remain limited and heterogeneous. Thus, while promising, bakuchiol still requires further investigation to confirm its sebum-regulating efficacy as a single ingredient.

L-carnitine to reduce sebum accumulation.

Naturally produced in the body, L-carnitine plays a crucial role in human energy metabolism by enhancing β-oxidation, the catabolic process by which fatty acids are broken down. In an in vitro study, human sebocytes were treated with 0.5% or 1% L-carnitine, resulting in a concentration-dependent increase in β-oxidation and a decrease in intracellular fatty acid content compared with untreated control cells, which would lead to a reduction in triglyceride accumulation within sebum lipid droplets.

To determine whether the data in vitro obtained could be applied to an in vivo situation, a randomised, vehicle-controlled clinical trial was conducted in 21 female volunteers. They applied a 2% L-carnitine formulation to one half of their face twice daily for three weeks. It was found that L-carnitine reduced the sebum secretion rate compared with controls. Although further studies assessing the efficacy of L-carnitine’s sebo-suppressive properties are warranted, this ingredient appears promising for recommendation to individuals concerned about oily skin.

Niacinamide (vitamin B3), the multifunctional active ingredient for regulating sebaceous lipogenesis.

In order to better understand the efficacy of niacinamide in acne, viable human tissue obtained from facelift surgeries was treated with niacinamide for four days. It was observed that niacinamide significantly reduces total sebaceous lipogenesis in a dose-dependent manner, an effect likely attributable to a reduction in triglycerides, which represent the predominant proportion of sebaceous gland lipids (up to 57.5%).

Moreover, in 2006 a placebo-controlled, double-blind clinical trial was conducted by K. Smiles and colleagues. It showed that a hydrophilic gel containing 2 % nicotinamide and 1 % D-panthenol, applied twice daily to the entire face of 100 subjects, significantly reduced sebum levels by approximately 30 % after four weeks of use. Based on these preliminary data, the topical niacinamide appears to be beneficial for oily skin. However, further studies are required to elucidate its mechanism of action.

Retinoids to modulate the lipid synthesis of sebocytes.

The biological effects of retinoids on the skin are based on their ability to interact with nuclear receptors, the retinoic acid receptors (RAR; isotypes α, β, γ), which form complexes with retinoid X receptors (RXR; isotypes α, β, γ). Furthermore, one study revealed that all of these receptors have been identified in human sebocytes. Moreover, a study in vitro demonstrated that retinoids can regulate the proliferation and differentiation of sebocytes by modulating keratin expression as well as lipid synthesis.

In light of these findings, it is therefore postulated that a topical retinoid would bind to these specific receptors on sebocytes, thus causing a reduction in sebum production. However, to date there is no direct evidence demonstrating that topical retinoids clearly exert a sebo-suppressive effect.

Sarcosine, an amino acid derivative that controls surface hyperseborrhoea.

The sarcosine is the N-methylated derivative of glycine, an amino acid naturally found in human body tissues. It has been reported to be a valuable ingredient for restoring balance to oily skin. According to certain studies, sarcosine applied topically regulates excess sebum, shine and oiliness of the skin. It exerts this effect by inhibiting the activity of 5α-reductase, an enzyme responsible for converting testosterone into dihydrotestosterone, which in turn promotes sebum production.

Indeed, a clinical study conducted on women aged 21 to 49 years demonstrated a statistically significant reduction in sebum levels on the skin surface after two weeks of twice-daily application of a topical formulation containing sarcosine. However, although this initial study is promising, further investigations are needed to better understand the sebostatic action of sarcosine on oily skin.

Green tea and its sebum-regulating potential.

Another ingredient whose efficacy on oily skin has been proven is the green tea (Camellia sinensis). In a small study conducted in 2010, ten male volunteers applied a topical emulsion containing 3% ethanolic green tea extract to their cheeks over an eight-week period. A statistically significant reduction in skin sebum production (≈ 60%) relative to baseline was observed throughout the study period.

Another study with a slightly larger cohort (n = 22 male participants) also revealed a consistent and significant reduction in sebum secretion after 60 days of applying a topical green tea emulsion to one half of the face. Based on these findings, topically administered green tea appears beneficial for individuals with oily skin. It is suggested that this activity is due to the ability of epicatechin gallate (ECG) and epigallocatechin gallate (EGCG), the primary active constituents of green tea, to selectively inhibit the 5 α-reductase enzyme in the sebaceous glands.

Vitamin D and its analogues: a new approach to counteracting excess sebum?

Human sebocytes, the cells responsible for production of sebum, appear to express vitamin D receptors (VDR) as well as the enzymes required for the synthesis and metabolism of its biologically active form (calcitriol). Studies in vitro have shown that exposure to calcitriol or certain vitamin D analogues can inhibit sebocyte proliferation, arrest their growth cycle and reduce their lipid production in a dose-dependent manner, suggesting a potential sebo-regulatory effect.

However, it should be emphasised that these observations stem exclusively from studies conducted on cellular models in vitro. To date, no clinical trial has yet confirmed these effects in humans. Further research will therefore be required to substantiate their potential as topical actives for oily skin.

Zinc, atrace element with anti-androgenic and sebum-suppressive action.

Certain studies seem to indicate that thetrace element zinc may have sebum-suppressive activity. Indeed, results have shown that it plays a regulatory role in testosterone metabolism with a local anti-androgenic action. Notably, zinc has been reported to inhibit, in vitro, the enzymatic activity of 5α-reductase, which is primarily present in sebaceous glands, in a dose-dependent manner via various mechanisms.

Although further data are required to confirm zinc’s action on sebum production, an initial randomised, double-blind clinical trial reported that topical application of a lotion containing a complex of erythromycin (4%) and zinc (1.2%) in 14 volunteers induced a significant reduction in sebum excretion rate of over 20% compared with the control lotion (4% erythromycin) after 12 weeks. These findings suggest that the effect on sebum production may be attributed to the zinc in the formulation.

Aside from these actives, there are also ingredients referred to as mattifying (sulphur, silica, clay, charcoal, bamboo extract, etc.), capable of reducing the shiny appearance of oily skin primarily through absorption of excess sebum on the skin surface.

• MOWSZOWICZ I. & al. Inhibition of 5 α-reductase activity in human skin by zinc and azelaic acid. British Journal of Dermatology (1988).

• ORFANOS C. E. & al. Effects of 13-cis-retinoic acid, all-trans-retinoic acid, and acitretin on the proliferation, lipid synthesis and keratin expression of cultured human sebocytes in vitro. Journal of Investigative Dermatology (1991).

• PIÉRARD G. E. & al. A double-blind controlled evaluation of the sebosuppressive activity of topical erythromycin-zinc complex. European Journal of Clinical Pharmacology (1995).

• BURTON E. & al. Regulation of sebum production by niacinamide. 60th Annual Meeting American Academy of Dermatology, New Orleans (2002).

• SMILES K. & al. The effect of 2% niacinamide on facial sebum production. Journal of Cosmetic and Laser Therapy (2006).

• REICHRATH J. & al. Characterization of the vitamin D endocrine system in human sebocytes in vitro. Journal of Steroid Biochemistry and Molecular Biology (2009).

• ZOUBOULIS C. C. Sebaceous gland receptors. Dermato-Endocrinology (2009).

• SAEED T. & al. Outcomes of 3% green tea emulsion on skin sebum production in male volunteers. Bosnian Journal of Basic Medical Sciences (2010).

• MARCHIO F. & al. Bakuchiol in the management of acne-affected skin. Cosmetics and Toiletries (2011).

• WENCK H. & al. Topically applied L-carnitine effectively reduces sebum secretion in human skin. Journal of Cosmetic Dermatology (2012).

• MOLDOVAN C. & al. A comparison of the effects of topical green tea and lotus on facial sebum control in healthy humans. Hippokratia (2013).

• GRANGER C. & al. Clinical evidence of the efficacy and safety of a new 3‐in‐1 anti‐aging topical night serum‐in‐oil containing melatonin, bakuchiol, and ascorbyl tetraisopalmitate- 103 females treated from 28 to 84 days. Observational Study (2018).

• YATSKAYER M. & al. Clinical evaluation of the efficacy of a topical product containing sarcosine on subjects with normal to oily skin types residing in warm and humid environments. Journal of the American Academy of Dermatology (2021).

• ERKIERT-POLGUJ A. & al. Long-term effect of azelaic acid peel on sebum production in acne. Dermatologic Therapy (2022).

• PARK S. J. A comprehensive review of topical bakuchiol for the treatment of photoaging. Journal of Integrative Dermatology (2022).

• SODHA P. & al. The use of bakuchiol in dermatology: A review of in vitro and in vivo evidence. Journal of Drugs in Dermatology (2022).