L-carnitine: what essential facts do you need to know?

What is L-carnitine?

L-carnitine is a molecule naturally present in the body, derived from the amino acids lysine and methionine. It is particularly useful for energy metabolism and facilitates the transport of long-chain fatty acids to the mitochondria, regarded as the powerhouses of the cell, where they are used to produce ATP. L-carnitine is therefore essential for the proper functioning of the organism. From a biochemical perspective, carnitine corresponds to 3-hydroxy-4-trimethylammoniobutanoate. It exists in two forms, known as stereoisomers: D-carnitine, the inactive form, and L-carnitine, the biologically active form.

The human body can synthesise L-carnitine in adequate quantities under normal conditions, thanks to contributions from the liver, kidneys and brain. It is also present in the diet, primarily in red meat and certain animal-derived products. However, its levels can vary according to age, health status, dietary choices or exercise habits. L-carnitine It therefore attracts particular interest in both medical and nutritional fields, and its use as a dietary supplement is becoming increasingly common.

Did you know? Carnitine derives its name from the Latin word carnis, meaning "meat".

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What is the process for obtaining L-carnitine?

L-carnitine can be obtained by two primary routes: through endogenous synthesis in the body or by industrial production for use in dietary supplements and cosmetic applications.

Endogenous synthesis of L-carnitine : It depends on the presence of lysine and methionine, two amino acids, as well as several cofactors, such as vitamin C, vitamin B6, niacin and iron. These components participate in various enzymatic steps, allowing the progressive conversion of methylated lysine into functional L-carnitine. This process is especially active in the liver and kidneys, from where the molecule is subsequently transported to peripheral tissues.
Industrial production of L-carnitine : It is typically carried out by microbial fermentation or by stereospecific chemical synthesis. Fermentation employs microorganisms capable of converting precursors such as trimethyllysine into L-carnitine via an enzymatic cascade, such asEscherichia coli. Chemical synthesis, on the other hand, relies on the assembly of basic organic structures, but it must be carefully controlled to prevent the formation of the D enantiomer, only the L form being biologically active.

L-carnitine: what are its cosmetic benefits?

Although L-carnitine is best known for its role in cellular energy metabolism, it is also increasingly sought after in cosmetics, whether for skin care or hair care.

The L-carnitine for the care of oily skin : L-carnitine may initially regulate sebum production. By promoting the transport of long-chain fatty acids to the mitochondria, it decreases the availability of intracellular lipids required for sebum synthesis in the sebaceous glands. This effect has been confirmed in various clinical trials, including the one presented below.

Number of participants	Distribution of participants	Protocol	Results
90	3 groups: cream with 2% L-carnitine, 5% EGCG (a polyphenol extracted from green tea) or a combination of the two.	Apply twice daily for four weeks.	Reduction in sebum secretion by 34.8% with L-carnitine, 41.4% with EGCG and 43.5% with the combination.

The effects of L-carnitine on oily skin.

Source: DETUDOM P. & al. Efficacy of anti-sebum moisturizing cream containing 2% l-carnitine and 5% epigallocatechin gallate in seborrhea: A randomized clinical trial. Journal of Cosmetic Dermatology (2023).

L-carnitine could help maintain skin firmness : The L-carnitine is also beneficial for delaying the onset of wrinkles thanks to its antioxidant properties, which enable it to limit the degradation of collagen and elastin fibres by free radicals. Furthermore, studies in vitro showed that it inhibits the activity of the metalloproteinases MMP-1 and MMP-2, enzymes involved in the degradation of the dermal matrix. These mechanisms manifest clinically: a study conducted on 50 women showed that after 12 weeks of applying a cream containing 1% L-carnitine, skin roughness was significantly reduced compared with placebo, with improved texture and visibly reduced wrinkles.

Effets de la L-carnitine sur les rides. — Comparison of the crow’s-foot wrinkle indices of volunteers after 8 (a) and 12 (b) weeks of treatment.
Source: BUM-CHUN L. & al. Anti-aging effects of L-carnitine on human skin. Journal of the Society of Cosmetic Scientists of Korea (2004).

L-carnitine could soothe skin inflammation : L-carnitine might also help to soothe sensitised skin. Studies in vitro have shown that it can decrease levels of pro-inflammatory cytokines, such as TNF-α, and the p-NFκB marker, emphasising an overall anti-inflammatory action. Moreover, a clinical trial assessed a formulation combining L-carnitine, biotin, panthenol, bisabolol and α-tocopherol in 30 patients with eczema. For three weeks, participants applied the product or a placebo twice daily. The results demonstrated a significant improvement in lesions (erythema, vesicles, scaling) as well as a reduction in itching in the treated group. However, it remains difficult to know how decisive the inclusion of L-carnitine in the formulation was.

Évolution de l'érythème et du prurit associés à l'eczéma. — Progression of erythema and pruritus associated with eczema.
Source: MESSINESE S. et al. Topical treatment of contact dermatitis with natural active principles. Journal of Plastic Dermatology (2013).

L-carnitine could promote skin healing : The L-carnitine could support skin wound healing by acting on several stages of the repair process. It promotes fibroblast proliferation, stimulates collagen synthesis and accelerates re-epithelialisation, thereby contributing to a faster and more robust reconstruction of the skin tissue. At the same time, its antioxidant and anti-inflammatory properties help to limit oxidative stress and local inflammation, two factors that can delay healing.
L-carnitine may be able to reduce cellulite : The L-carnitine could help diminish the appearance of cellulite by promoting the mobilisation of fats stored in adipocytes. By facilitating the entry of fatty acids into mitochondria via the carnitine–palmitoyl transferase 1 (CPT1) complex, it boosts their oxidation and leads to reduced cell volume. This is why topical application of L-carnitine, notably in combination with caffeine, has been linked to reductions in thigh circumference and body fat in certain clinical trials, including the one presented below carried out with 10 volunteers over 28 days.

Group	Reduction in thigh circumference	Reduction in localised fat mass
L-carnitine group	1.2 cm	100 g
Placebo group	0.8 cm	57.3 g

Thigh circumference and fat mass before and after the study.

Source: RODRIGUEZ J. & al. Effects of a topical lotion containing aminophylline, caffeine, yohimbe, L-carnitine, and gotu kola on thigh circumference, skinfold thickness, and fat mass in sedentary females. Journal of Cosmetic Dermatology (2019).

L-carnitine could stimulate hair growth : The L-carnitine could also protect hair from loss. A study in vitro has shown that L-carnitine-L-tartrate (CT), when applied to human anagen phase hair follicles, promoted hair shaft elongation: follicles treated with concentrations ranging from 0.5 to 5 µM exhibited a 37% increase in hair length compared with the control group. However, while these results are promising, only a few clinical trials have been conducted to date, and further research is required to confirm the efficacy of L-carnitine on hair growth.

Effets de la L-carnitine sur la pousse des cheveux. — Hair shaft elongation in millimetres (a) and percentage (b) after treatment of hair follicles with different concentrations of L-carnitine-L-tartrate.
Source: Paus R. et al. L-carnitine L-tartrate promotes human hair growth in vitro. Experimental Dermatology (2007).

Are there any known risks or contraindications associated with the use of L-carnitine?

L-carnitine is regarded as a well-tolerated active ingredient, even for sensitive skin.

Studies conducted on the L-carnitine at concentrations typically ranging from 0.5% to 2% have reported no adverse effects (no redness, irritation or itching). Regarding vulnerable populations such as pregnant or breastfeeding women and young children, the data are limited. Nevertheless, nothing suggests that the topical use of L-carnitine poses a risk to these groups. As a precaution, however, women planning to become pregnant are advised to consult their doctor before use.