L-carnitine: what are its beneficial properties for the skin?

The L-carnitine is part of the new generation of interesting active ingredients for oily skin due to its role in cellular energy metabolism. This molecule acts as a carrier for long-chain fatty acids, transporting them to the mitochondria to be oxidised and converted into energy. In the sebaceous glands, a significant portion of sebum production depends on the availability of these fatty acids. By stimulating their utilisation by the mitochondria, L-carnitine could limit the intracellular lipid reservoir, and thus reduce sebum synthesis.

A study in vitro carried out on a human sebaceous cell line (SZ95) confirmed the benefits of L-carnitine for oily skin. When these cells were exposed to 0.5% and 1% concentrations of L-carnitine, they showed a significant increase in β-oxidation, that is, the process by which mitochondria break down fatty acids. At the same time, intracellular lipid levels decreased in a dose-dependent manner, reflecting a reduction in the pool available for sebum synthesis. Beyond these results in vitro, several clinical studies have also highlighted the benefits of L-carnitine for oily skin.

The ability of L-carnitine to reduce sebum production renders it of particular interest in the management of acne. Indeed, excess sebum is one of the key factors in this condition, as it favours the obstruction of pilosebaceous follicles and the proliferation of Cutibacterium acnes, a bacterium involved in the development of inflammatory lesions. By regulating the availability of intracellular fatty acids and thus the amount of sebum produced, L-carnitine could limit the formation of comedones and reduce the severity of acne flare-ups.

A clinical study investigated this effect by evaluating an innovative therapeutic combination in 29 volunteers with mild to severe acne. The protocol involved photodynamic therapy (PDT, using intense pulsed light of 400–720 nm, administered in four sessions at two-week intervals), combined with a cream containing L-carnitine, licochalcone A and decanediol, applied twice daily for ten weeks. The other group received the same protocol but with a placebo cream. The results showed a faster and more effective reduction in lesion count in the 'L-carnitine' group. However, it is important to emphasise that these outcomes cannot be attributed to L-carnitine alone: the observed efficacy is based on a cream combining multiple active ingredients (L-carnitine, licochalcone A and decanediol) and on its concurrent use with photodynamic therapy.

The L-carnitine could also be of interest in combating skin ageing. Indeed, it has antioxidant properties that enable it to neutralise free radicals generated notably by UV radiation, which are responsible for the breakdown of collagen and elastin. Meanwhile, studies in vitro have shown that L-carnitine inhibits the activity of the matrix metalloproteinases MMP-1 and MMP-2, enzymes that contribute to the degradation of the dermal matrix under oxidative stress. By combining these two actions, L-carnitine would thus help preserve skin elasticity and firmness.

Good to know : The antioxidant properties of L-carnitine may also help to make the complexion more radiant.

These hypotheses were confirmed in a clinical study carried out on 50 women, divided into two groups: one using a cream containing 1% L-carnitine, the other a placebo. After 12 weeks of twice-daily application to the whole face, visiometry assessment showed a significant reduction in two skin roughness parameters (R2 and R3) in the L-carnitine group, reflecting a visible improvement in skin texture and a reduction in wrinkles compared with the placebo. No adverse effects were reported, confirming the good tolerability of the active ingredient. These results suggest that L-carnitine could play an interesting role in the prevention and attenuation of skin ageing.

Pruritus is a common symptom that accompanies many conditions. It can occur occasionally, for example after an insect bite, or develop in a chronic context, such as in the eczema. These itch sensations, often trivialised, nevertheless impair quality of life and reflect inflammatory and oxidative imbalances in the skin.

In this context, L-carnitine has demonstrated interesting anti-inflammatory and anti-pruritic properties. An experimental study evaluated its effects in a murine model of chloroquine-induced pruritus. The results show that oral administration of L-carnitine significantly reduced scratching behaviour compared with the control group, confirming its antipruritic potential. Biologically, the compound restored the balance of antioxidant defences (GST, GSH and catalase) while reducing lipid peroxidation (LPO). It also decreased nitric oxide synthase (NOS) activity, thereby modulating the nitric oxide pathway involved in the genesis of itching. Finally, L-carnitine reduced levels of pro-inflammatory cytokines (TNF-α), pro-inflammatory enzymes such as COX-2, and the p-NFκB marker. Taken together, these effects suggest that L-carnitine acts both by limiting inflammation and by regulating oxidative stress, thus contributing to itch relief.

However, one must remain cautious, as this study was conducted in mice and relied on oral administration of L-carnitine, which limits extrapolation.

Moreover, other studies have reported interest in the L-carnitine for topical application to soothe eczema, but these studies combined the molecule with other active ingredients whose efficacy against eczema is already well documented. It therefore remains difficult to determine to what extent L-carnitine alone truly contributes to symptom improvement.

The wound healing process is a complex series of events that relies on several stages: initial inflammation, fibroblast proliferation, collagen synthesis and finally re-epithelialisation. Any disruption of this sequence can result in delayed healing, persistent skin fragility or hypertrophic scarring. Several active ingredients can support this process, potentially including L-carnitine.

An experimental study involving 60 rats assessed the effects of L-carnitine on the healing of skin wounds. The animals were assigned to three groups: a control group with no treatment, a group receiving local L-carnitine administration and a group receiving systemic administration, all monitored over 14 days. The researchers analysed the rate of wound healing, the quality of the repaired tissue and the mechanical strength of the wounds. They found that the average healing time was markedly reduced in the groups treated with L-carnitine, whether administered orally or applied topically. Furthermore, the treated rats exhibited a faster re-epithelialisation and more abundant collagen deposition.

However, as these data were obtained from an animal model, it remains necessary to confirm these effects in humans before considering clinical application.

Applied topically, L-carnitine is thought to promote fat breakdown by facilitating the entry of fatty acids into adipocyte mitochondria via the enzymatic complex carnitine-palmitoyltransferase 1 (CPT1). This permits the formation of acyl-carnitine, which crosses the mitochondrial membrane and is then reconverted into acyl-CoA, thereby initiating β-oxidation. This mechanism results in a reduction in adipocyte volume, which could mitigate the lipid overload observed in cellulite. At the same time, L-carnitine also appears to regulate oxidative stress, a factor that exacerbates fibrosis and inflammation in cutaneous tissues. By reducing lipid peroxidation and protecting collagen and elastin fibres, it may help preserve the integrity of connective tissue.

A clinical trial investigated this hypothesis by testing a cream containing L-carnitine and caffeine, applied daily for 28 days in seven female participants who also followed a calorie-restricted diet and a weekly walking programme. Compared with placebo, the tested treatment induced a more pronounced reduction in thigh circumference and fat mass, as measured by dual-photon absorptiometry.

These findings suggest a potential role for L-carnitine in ameliorating cellulite, but their scope remains limited by the small number of participants and the presence of other actives known for their lipolytic properties. Thus, it is difficult to attribute the observed effect solely to L-carnitine, and larger-scale studies remain necessary to confirm its true efficacy.

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