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

Oily skin (+) is a common dermatological concern. Although sebaceous glands play a crucial role in the skin's barrier function by providing the stratum corneum with waterproofing properties, they are also responsible for the excessive production of sebum, giving the skin an undesirable shiny appearance and larger pores. Numerous factors have been suggested to play a role in the pathogenesis of oily skin. However, active ingredients have been identified to regulate sebum production through various points of action.

Azelaic Acid.

Theazelaic acid is believed to be one of the substances that regulate the functioning of the sebaceous glands. As demonstrated by a study conducted by ERKIERT-POLGUJ A. and colleagues among 27 women aged between 19 and 25, 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 average amount of sebum was 195.5 before treatment and 162.7 after the six treatments; as for the values on the cheek, they averaged 175.3 before treatment versus 141.3 after the sixth application of azelaic acid.

The mechanism of action behind this sebostatic activity is the inhibition of 5 α-reductase, an enzyme that leads to an amplification of androgenic activity accompanied by excessive sebum production (hyperseborrhoea). It has been suggested that this inhibition may be due to azelaic acid competitively occupying the NADPH binding site of 5 α-reductase. Therefore, azelaic acid appears to represent a potential therapeutic agent against oily skin.

L-carnitine.

Naturally produced within the body, L-carnitine plays a pivotal role in human energy metabolism by enhancing β-oxidation, a catabolic process through which fatty acids are broken down. In a study in vitro, human sebocytes were treated with 0.5% or 1% L-carnitine, and this led to a significant increase in β-oxidation and a decrease in intracellular fatty acid content relative to untreated control cells, which would result in a reduction of triglyceride accumulation in the sebum's lipid droplets.

To determine whether the data in vitro can be applied to a situation in vivo, a randomised, vehicle-controlled clinical trial was conducted on 21 participants. The volunteers were required to apply a formulation containing 2% L-carnitine to half of their face, twice daily for three weeks. It was found that L-carnitine possesses characteristics of reducing sebum secretion rates compared to controls. Although further studies evaluating the efficacy of L-carnitine's sebosuppressive properties are warranted, this ingredient appears to be interesting to recommend to individuals concerned with oily skin.

Niacinamide.

In order to better understand the effectiveness of niacinamide on acne, viable human tissues from facelift surgeries were treated with niacinamide for four days. It was found that niacinamide significantly reduces total sebaceous lipogenesis, depending on the dose used, with an effect likely attributable to a reduction in triglycerides which represent the predominant proportion of lipids in the sebaceous glands (up to 57.5%).

Furthermore, in 2006, a double-blind placebo-controlled clinical study was conducted by SMILES K. and his team. It was demonstrated that the hydrophilic gel containing 2% nicotinamide and 1% D-panthenol, applied to the entire face twice a day in 100 subjects, significantly reduced sebum levels by about 30% after four weeks of use. From these initial data, the topical niacinamide appears to be beneficial for oily skin. However, further studies are needed to describe the mechanism of action.

Retinoids.

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 complex with retinoid X receptors (RXR; isotypes α, β, γ). Furthermore, a study has revealed that these receptors have all been identified in human sebocytes. Additionally, a study in vitro has demonstrated that retinoids have the ability to regulate the proliferation and differentiation of sebocytes by modulating the expression of keratin, as well as lipid synthesis.

In light of these findings, it is thus hypothesised that a topical retinoid would bind to these specific receptors at the level of the sebocytes, which would then cause a reduction in sebum production. However, there is currently no direct evidence demonstrating that topical retinoids clearly have a sebum-suppressing effect.

Sarcosine.

Sarcosine is the N-methyl derivative of glycine, an amino acid naturally present in human body tissues. It has been reported to be a promising ingredient for rebalancing oily skin. According to some studies, when applied topically, sarcosine could regulate excess sebum, skin shine and oiliness. It is believed to exert this effect by inhibiting the activity of 5 α-reductase, an enzyme responsible for converting testosterone into dihydrotestosterone, which in turn promotes sebum production.

Indeed, a clinical study conducted on women aged between 21 and 49 years demonstrated a statistical reduction in the level of sebum on the skin's surface after two weeks of twice-daily use of a topical formulation containing sarcosine. However, although this initial study is promising, further investigations are necessary to better understand the sebostatic action of sarcosine on oily skin.

Green tea.

Another ingredient that has been proven to be effective when applied to oily skin is the green tea (Camellia sinensis). In a small study conducted in 2010, 10 male volunteers applied a 3% topical emulsion of standardised green tea extract to their cheeks over a period of eight weeks. A statistically significant reduction in skin sebum production (≈ 60%) was observed compared to the initial value 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. From these results, topically administered green tea proves 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 main active constituents of green tea, to selectively inhibit the enzyme 5 α-reductase in the sebaceous glands.

Zinc.

Some studies appear to suggest that thetrace element zinc may have sebum-suppressing activity. Indeed, results have shown that it plays a regulatory role in testosterone metabolism with a local anti-androgenic action. It has been reported in particular that zinc can inhibit, in vitro, the enzymatic activity of 5 α-reductase, which is primarily present in the sebaceous glands, in a dose-dependent manner through various mechanisms.

Although additional data is required to confirm the impact of zinc on sebum production, an initial randomised double-blind clinical study reported that the topical application of a lotion containing a complex of erythromycin (4%) and zinc (1.2%) in 14 volunteers led to a significant reduction in sebum excretion rate of over 20% compared to the control lotion (4% erythromycin) after 12 weeks. These results seem to suggest that the effect on sebum production could be attributed to the zinc contained in the preparation.

Beyond these active ingredients, there are also so-called mattifying ingredients (sulphur, clay, charcoal, bamboo extract, etc.), capable of reducing the shiny appearance of oily skin more by absorbing the excess sebum on the skin's surface.