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CITRIC ACID - AHA
Principal indications: dull complexion, loss of radiance
PURE ACTIVE A60
Bibliographical summary
 
  • INCI name :CITRIC ACID
  • Molecule more than 91% pure obtained by biotechnology
 

Loss of radiance in the complexion may be the result of the waxy complexion typical of oily skin associated with dilated pores or one of the consequences of skin ageing due to:
• The thickening of the corneous layer by the accumulation of corneocytes, which impair the transparency of the epidermis
• The thinning of the living epidermis
• The slowdown of the activity and turnover (renewal) of the keratinocytes
• Increased and irregular melanocyte density
Capable of modifying the cohesion of the corneocytes and thus accelerating the desquamation process, AHAs will modulate epidermal renewal.
In comparison with other AHAs, citric acid also has an astringent property that helps to close up dilated pores and give a finer complexion (a property widely recognized and, in general, related to the traditional use of lemon).

 

  • ACTION MECHANISMS / PROOFS OF EFFECTIVENESS

Owing to the multiplicity of their actions, AHAs are capable of acting on numerous parameters:
• Keratolytic/desquamating effect:
AHAs modify the strength of the intercorneocyte bonds by reducing the electronegativity of the corneocytes. The corneocytes bear positive ionic charges (amine groups of the basic amino acids constituting their cell membranes) and negative charges (linked to phosphate and sulphate groupings, also membranous). Forces of attraction are established between these opposite charges. By competing with the "binding" enzymes in the sulphate and phosphate groupings on the surface of the corneous cells, the AHAs replace these enzymes and prevent these groupings from binding. This brings about a reduction in their density, leading to a drop in electronegativity. As the cohesive forces are weakened, desquamation is facilitated [1].
• Regulation of moisturization:
AHAs provide moisturization, thanks to their hygroscopic and plasticizing abilities, by being adsorbed to the polar groups of keratin. Thanks to their moisturizing power, AHAs here again modify the ionic intercorneocyte bonds for, when the stratum is moisturized, the distance between the corneocytes is increased and the binding forces are therefore reduced [1].
• Acceleration of epidermal renewal:
The "surface peeling" effect of AHAs leads to a reduction in the thickness of the corneous layer. This phenomenon is accompanied by an increase in the thickness of the living epidermis and an acceleration of epidermal renewal, seen particularly at the start of treatment [1].
• Effects on the constituents of the dermis and the epidermis:
AHAs stimulate GAG (glycoaminoglycan) production in the dermis and the epidermis. Citric acid at 20% (applied twice a day for 3 months) increases the dermal and epidermal GAG content [1, 2]. Citric acid at 25% (applied twice a day for 6 months) increases the density of the elastic and collagen fibres in the dermis [1, 3].
The stimulant effects on the epidermis restart fibroblastic activity, as in the epidermal cicatrization process.
These effects are thought to be involved in the increase of skin thickness observed during treatment with AHAs.
• Pigmentation control:
It has been shown in skin biopsies that treatment with citric acid at 25% (applied twice a day for 6 months) brings about better, more homogenous epidermal distribution of melanin [3].
• Comment:
AHAs (alpha hydroxy acids) are recognized in particular for their powerful keratolytic activity, thanks to their acid carboxylic function, as well as for their tolerance problem. It has been clearly demonstrated in the literature that the acid pH of concentrated AHA preparations was responsible for any irritations. [Kneedler J, Sky S, Sexton L. Understanding Alpha Hydroxy Acids. Dermatology Nursing; August 1998/Vol.10/No.4]
Citric acid is an AHA, the particularity of which is that it comprises 3 carboxylic functions.
Depending on the surrounding pH, these carboxylic functions will be either acid (COOH) or basic (COO-). A pKa is attributed to each of these 3 carboxylic functions, which corresponds to the pH value at which the carboxylic function in the basic state becomes acid.
At a cutaneous pH of 5.5, the citric acid with one of its pKas at 6.4 will have one acid function and 2 basic functions (pKa 4.76 and 3.13).
At a pH of 5.5, the effectiveness/tolerance trade-off seems to be the best.

 

  • OUR EXPERT'S OPINION

Citric acid belongs to the AHA family in which the shortest molecule is glycolic acid. It is a triacid with 3 similar pKas, which have the advantage of a broader buffer range. Tolerance is considered better than that of smaller AHAs (lactic, glycolic).
The effect of this chemical series requires the formation of hydrogen bonds and complexes based on the presence of hydrogen on the acid function. Formulations must therefore be made in such a way as to provide an acid environment, pH below the pKa (3.5-4). Tolerance and effectiveness are governed by the pH and the concentration.
The desquamation and cleansing of ichthyotic lesions have been well demonstrated. The corneous layer improves rapidly and improved water bonding is possible (a few days).
By extension, the repeated "peeling" effect will stimulate the epidermis and the dermis. Effects in photo-ageing, similar to retinoic acid, are obtained (but with a different mechanism).
Over approximately one month, the skin adapts to the inflammation and tingling sensations felt on application. Rapid effects can be seen (renewed radiance), but the measurable effects on wrinkles may require several months to be considered objectively.
The best results are obtained with high concentrations in the order of 20% acid and a pH of less than 4. Clearly, here again, the formulation creates a balance between effectiveness and tolerance, which is unique to the compromise sought by the formulation technician. However, one must be aware that the occasionally unpleasant effects on initial application are a sign that the product works!

 

  • EFFECTIVE DOSE

The body of publications and scientific studies, customary usages of this active and our expert's opinion concur in using Citric Acid pure Active at the dose of 3000 mg per bottle.

 

  • BIBLIOGRAPHICAL REFERENCES

[1] Alpha-hydroxy-acides et vieillissement cutané. Gougerot-Schwartz A. Encycl Méd Chir, Cosmétologie et Dermatologie esthétique, 50-160-C-12, 7p. 2000.
[2] Citric acid increases viable epidermal thickness and glycosaminoglycan content of sun-damaged skin. Bernstein EF et al. Dermatol Surg. 23(8):689-94. 1997.
[3] Effects of alpha-hydroxy acids on photoaged skin: a pilot clinical, histologic, and ultrastructural study. Ditre CM et al. J Am Acad Dermatol. 34(2 Pt 1):187-95. 1996.

 

This information is given for informative purposes. In no event does it constitute medical information, nor engage our liability. These documents may be copied and reproduced exclusively for informative purposes for personal and private use. All and any use of copies or reproductions for other purposes is expressly forbidden and shall engage the user's liability under Article L 122-3 of the Intellectual Property Code.