1 The Role of Succinic Acid in Acne Care

1.1 Acne Development Involves Multiple Interrelated Processes

Acne develops within the pilosebaceous unit and mainly involves the following changes:

① Changes in sebum secretion and sebum composition

Changes in androgen activity, sebaceous gland activity, and local metabolic status create an environment within the follicle that is more conducive to lipid accumulation and microbial metabolism.

② Abnormal follicular keratinization

Impaired shedding of keratinocytes in the follicular infundibulum causes keratin and sebum to gradually form microcomedones, which may further develop into closed or open comedones.

③ Changes in the composition and metabolic activity of follicular microorganisms

The acne-associated skin bacterium Cutibacterium acnes, abbreviated as C. acnes, was formerly known as Propionibacterium acnes or the acne propionibacterium. C. acnes is present on both healthy and acne-prone skin, and different strains vary in the extent to which they are associated with acne [2–3].

④ Inflammatory responses in the follicular wall and surrounding tissues

Expansion of the keratin plug, sebum oxidation, microbial metabolites, and host immune responses collectively promote the formation of papules, pustules, and nodules.

Succinic acid cannot simultaneously act on all of the above processes. Its main research value is concentrated in the third process, namely, assisting in the modulation of acne-associated microbial activity by influencing the acid–base environment and microbial metabolic conditions. Evidence for its direct effects on follicular keratinization and sebum secretion remains relatively limited.

1.2 Evidence for the Effects of Succinic Acid Exists at Different Levels

The potential effects of succinic acid can currently be divided into three levels:

2 Chemical Nature of Succinic Acid

2.1 Molecular Structure

The systematic name of succinic acid is butanedioic acid. Its molecular formula is C₄H₆O₄, its relative molecular mass is approximately 118.09, and its structural formula is:

HOOC—CH₂—CH₂—COOH

It is an aliphatic dicarboxylic acid containing one carboxyl group at each end of the molecule, connected by two methylene groups [1].

This structure has three important characteristics:

① The molecule is relatively small and can be readily dispersed in the aqueous phase of a formulation;

② It contains two carboxyl groups that can dissociate stepwise;

③ It contains neither an aromatic ring nor a long hydrophobic carbon chain, giving it lower lipid affinity than salicylic acid.

2.2 Two-Step Acid Dissociation

Succinic acid can release hydrogen ions in two steps:

First dissociation:

H₂Suc ⇌ H⁺ + HSuc⁻  pKₐ₁ is approximately 4.2

Second dissociation:

HSuc⁻ ⇌ H⁺ + Suc²⁻  pKₐ₂ is approximately 5.6

Where:

· H₂Suc represents undissociated succinic acid;

· HSuc⁻ represents hydrogen succinate;

· Suc²⁻ represents succinate.

The formulation pH determines the relative proportions of these three forms. Based on acid–base equilibria in an ideal aqueous solution, the following approximate values can be obtained:

At lower pH, the proportion of undissociated succinic acid is higher. As the pH increases, succinic acid exists mainly in negatively charged ionic forms.

2.3 pH of Pure Succinic Acid and Succinic Acid Solutions

Pure succinic acid is a crystalline solid at room temperature.

The pH of a succinic acid solution depends on:

① Succinic acid concentration;

② Temperature and water quality;

③ Degree of neutralization;

④ Buffer salts and other electrolytes;

⑤ Other acids, bases, and polymers in the formulation.

Assuming a temperature of 25°C, pure water, and no added neutralizing agent, the following theoretical initial values can be calculated from the acid dissociation constants of succinic acid:

These values are theoretical estimates for ideal solutions and do not represent actual measurements of finished skincare products.

The term “weak acid” means that succinic acid does not dissociate completely in water. It does not mean that its aqueous solution is necessarily close to neutral. Unneutralized succinic acid at relatively high concentrations may still cause noticeable stinging and irritation.

3 Potential Anti-Acne Mechanisms of Succinic Acid

Available evidence allows the potential effects of succinic acid on the acne-associated microbial environment to be understood from four interrelated mechanistic perspectives.

3.1 Step 1: Lowering the Local pH

After dissolving in water, succinic acid releases hydrogen ions and lowers the pH of the formulation. Once the product comes into contact with the skin, it may temporarily influence the acid–base conditions at the skin surface and around the follicular opening.

Healthy skin surfaces are generally mildly acidic, although the exact pH is influenced by body site, age, cleansing practices, perspiration, and measurement conditions. Studies have shown that when interference from washing and skincare products is minimized, the average surface pH of healthy skin may be below 5 [5]. A mildly acidic environment also participates in the regulation of stratum corneum integrity and enzymes associated with barrier function [5–6].

Changes in pH may affect:

① The activity of extracellular bacterial enzymes;

② The proton gradient across the cell membrane;

③ The ionic state of nutrients and metabolic products;

④ Growth competition among different microorganisms.

This effect is not specific to succinic acid. Lactic acid, citric acid, and other organic acids can also lower pH.

3.2 Step 2: Undissociated Succinic Acid May Increase Acid Stress in Bacteria

The antimicrobial activity of weak organic acids is generally associated with the proportion of undissociated acid.

At lower pH, the proportion of undissociated succinic acid increases. Undissociated molecules carry no net charge and may interact more strongly with bacterial cell surfaces and membranes than negatively charged succinate ions.

The possible process is as follows:

Increase in extracellular undissociated succinic acid → contact with the bacterial cell membrane → some molecules may enter the cell or affect the membrane environment → disruption of intracellular acid–base balance and anion balance → increased energy expenditure by the bacterium to maintain the proton gradient → possible inhibition of growth and metabolism

This is a common mechanistic model for weak organic acids. For succinic acid and C. acnes, existing studies support an antimicrobial phenomenon, but the specific route by which succinic acid enters bacterial cells, its principal metabolic targets, and differences in susceptibility among strains have not yet been fully clarified.

3.3 Step 3: Fermentation Metabolites of Staphylococcus epidermidis Participate in Intermicrobial Antagonism Against C. acnes

The scientific name of the common skin bacterium Staphylococcus epidermidis is abbreviated as S. epidermidis. It is a common resident microorganism of the skin, and different strains may display commensal, competitive, or opportunistically pathogenic characteristics.

Studies have found that some S. epidermidis strains can ferment glycerol under appropriate conditions and produce metabolites including succinic acid. Fermentation products and exogenous succinic acid can inhibit the growth of P. acnes, now known as C. acnes, under experimental conditions and reduce related inflammatory responses in animal models [2].

The metabolic relationship can be represented as follows:

Available substrates such as glycerol → fermentation by S. epidermidis → formation of succinic acid and other organic acids → changes in the local acid–base and metabolic environment → restriction of the growth of some C. acnes strains

This study indicates that succinic acid may be one of the components involved in intermicrobial antagonism mediated by the fermentation metabolites of resident skin microorganisms. However, direct topical application of succinic acid is not equivalent to restoring the ecological function of S. epidermidis, nor does it establish that topical succinic acid can produce long-term modulation of the human skin microbiome.

In vitro culture and animal models cannot be directly equated with skincare efficacy in humans. Whether a topical product can produce similar effects also depends on:

① The effective concentration of succinic acid in the finished product;

② The final pH and proportion of undissociated acid;

③ The actual amount of product reaching the follicular opening and the interior of the follicle;

④ Contact time and frequency of use;

⑤ The effects of preservatives and other antimicrobial ingredients in the formulation.

3.4 Relationship Among Succinic Acid, Propionic Acid, and C. acnes

C. acnes was previously classified within the genus Propionibacterium. The former genus name Propionibacterium was associated with the ability of these bacteria to produce propionic acid through metabolism. In 2016, related skin-derived species were reassigned to the genus Cutibacterium based on systematic taxonomic research. Accordingly, Propionibacterium acnes is now known as Cutibacterium acnes [4].

The relationship between the two compounds mainly exists within the metabolic network of skin microorganisms. Different microbial species utilize glycerol, sebum-derived substances, and other carbon sources to produce different types of organic acids. These metabolites collectively influence local pH, nutrient competition, and microbial interactions.

3.5 Step 4: Indirect Modulation of Inflammation Through Reduced Microbial Stimulation

Some C. acnes strains, as well as their cellular components, enzymes, and metabolites, can stimulate follicular epithelial cells and immune cells. When bacterial growth or metabolic activity is inhibited, the associated inflammatory stimulation may also decrease.

Therefore, if succinic acid can inhibit the growth or metabolism of relevant strains under actual topical-use conditions, its potential influence on inflammatory lesions may arise through the following pathway:

Reduced microbial growth and metabolism → decreased microbial stimulation within the follicle → reduced local immune activation → possible attenuation of inflammatory manifestations

This process is indirect.

Succinate is also an intermediate of the human tricarboxylic acid cycle. Under specific immune-cell and pathological conditions, abnormal intracellular accumulation of succinate can participate in signaling associated with hypoxia-inducible factor-1α and interleukin-1β [7]. These conditions differ from exposure to low concentrations of topically applied succinic acid and therefore cannot be used directly to determine whether a topical product promotes or suppresses inflammation.

4 Succinic Acid Cannot Be Considered Equivalent to Salicylic Acid

The chemical name of salicylic acid is 2-hydroxybenzoic acid. Its molecular structure contains an aromatic benzene ring, a carboxyl group, and a phenolic hydroxyl group. Its aromatic hydrophobic structure gives salicylic acid greater lipid affinity than succinic acid. Under suitable pH and formulation conditions, it can distribute more readily into environments containing sebum and stratum corneum lipids [8–9].

Succinic acid lacks the aromatic hydrophobic structure of salicylic acid and may therefore have a lower tendency to distribute into the sebaceous environment of the follicle. Product vehicles can alter the skin distribution of an ingredient, but current evidence is insufficient to demonstrate that succinic acid has comedolytic activity comparable to that of salicylic acid.

5 Formulation Control of Succinic Acid

5.1 pH, Addition Level, and Titratable Acidity

When evaluating a succinic acid formulation, the following factors should be considered together:

① Total amount of succinic acid added;

② Final pH;

③ Degree of neutralization;

④ Titratable acidity;

⑤ Buffering capacity of the formulation.

pH reflects the activity of hydrogen ions in the aqueous phase. Titratable acidity reflects the total amount of acid in the system that can be neutralized by a base.

Even when two products have the same pH, they may contain different amounts of free acid and acid salts. A formulation with a higher total acid content and greater buffering capacity may continue to release hydrogen ions after contacting the skin or being partially neutralized by perspiration, and may therefore produce different efficacy and irritation profiles.

5.2 Neutralization Reactions and pH Adjustment

Succinic acid can be partially neutralized using sodium hydroxide, potassium hydroxide, arginine, tromethamine, or other suitable alkaline ingredients.

Using sodium hydroxide as an example:

H₂Suc + NaOH → NaHSuc + H₂O

With further neutralization:

NaHSuc + NaOH → Na₂Suc + H₂O

As the degree of neutralization increases:

① pH increases;

② The proportion of undissociated succinic acid decreases;

③ The proportion of succinate salts increases;

④ When total acid content and other formulation conditions are similar, the risk of immediate stinging generally decreases;

⑤ If the antimicrobial effect depends mainly on undissociated acid, the associated microbial inhibitory effect may weaken;

⑥ The electrolyte level of the system increases.

Formulators can establish multiple pH gradients and compare antimicrobial activity, stability, irritation, and skin feel before determining an appropriate range for the product type.

In practice, the following process may be used:

① Fully dissolve succinic acid in part of the aqueous phase;

② Measure the initial pH of the unneutralized system;

③ Pre-dilute the neutralizing agent;

④ Add it gradually under stirring;

⑤ Allow the system to equilibrate after each addition before measuring again;

⑥ Recheck the pH of the finished product after all ingredients have been added;

⑦ Continue monitoring pH drift during standing and stability testing.

5.3 Formulation Stability

Succinic acid partially dissociates in the aqueous phase. Succinate salts formed through partial or complete neutralization further increase the ionic strength of the system and may affect:

① The viscosity of carbomer and other acrylic thickeners;

② The stability of emulsion systems;

③ The solubility state of zinc salts and other metal ions;

④ The distribution and effectiveness of preservatives;

⑤ The crystallization behavior of other acidic ingredients.

The formulation should be evaluated under high-temperature, low-temperature, freeze–thaw, centrifugation, and long-term storage conditions for changes in pH, viscosity, color, odor, turbidity, and crystallization.

An acidic formulation cannot replace a complete preservative system. The finished product should still undergo preservative challenge testing based on the packaging format and intended conditions of use.

6 Combination Formulations and Evidence Evaluation for Succinic Acid

6.1 Combination with Salicylic Acid

Salicylic acid primarily targets follicular keratinization and keratin plug management, whereas succinic acid mainly affects the acid–base state of the aqueous phase and the microbial metabolic environment. The two have theoretical complementarity in their directions of action, but whether they produce actual efficacy synergy must still be verified through controlled testing of the finished formulation.

The following factors should be controlled in combined formulations:

① Whether salicylic acid is fully dissolved;

② Whether crystallization occurs during storage;

③ Whether the final pH is suitable for both ingredients;

④ Whether the total titratable acidity is excessively high;

⑤ Whether the preservative system remains effective.

6.2 Combination with Niacinamide and Barrier-Supporting Ingredients

Niacinamide, panthenol, ectoine, β-glucan, and physiological lipids can be used as combination ingredients for moisturization, barrier support, and evaluation of finished-product tolerability.

These ingredients do not directly enhance the acid dissociation of succinic acid. Whether they can reduce dryness or tightness associated with the use of an acidic formulation still depends on their addition levels, the formulation base, and finished-product testing.

Products containing both niacinamide and succinic acid should undergo accelerated stability testing to confirm product stability at the target pH, temperature, and storage period. Formulation conditions should not be determined solely on the basis of the recommended pH range of a single ingredient.

6.3 Combination with Azelaic Acid

Azelaic acid is also a dicarboxylic acid, but it has a longer carbon chain, and its lipid affinity, solubility, and effects on the skin differ from those of succinic acid. Compared with succinic acid, azelaic acid has accumulated more human clinical research data in acne treatment [2,11].

When the two are combined, the following factors should be evaluated:

① The dissolved or dispersed state of azelaic acid;

② Grittiness and application uniformity;

③ System pH;

④ Total acid load;

⑤ Cumulative irritation.

Increasing the number or concentration of acids does not mean that efficacy will increase proportionally.

6.4 Verification of Antimicrobial and Microecological Effects

Antimicrobial testing of succinic acid may include the following controls:

① A blank formulation without succinic acid;

② An acidified control adjusted to the same pH as the succinic acid sample;

③ Samples with different succinic acid concentrations but the same pH;

④ Samples with the same succinic acid concentration but different pH values;

⑤ A finished-product control containing the complete preservative system.

These controls can help distinguish:

· Effects caused solely by low pH;

· Effects caused by succinic acid and its acid anions;

· Nonspecific antimicrobial effects caused by preservatives;

· Differences in susceptibility among microbial strains.

7 Representative Chemicals Related to the Anti-Acne Mechanisms of Succinic Acid, Microbial Metabolic Competition, and Formulation Research

Table 1. Core Succinic Acid Systems and Microbial Metabolism-Related Compounds

Table 2. Products Related to pH Adjustment, Neutralization, and Buffer Systems

Table 3. Products Related to Anti-Acne Combination Strategies, Keratinization Management, and Tolerability Research

Note: The above products are mainly intended for chemical analysis, in vitro experiments, mechanistic research, and laboratory formulation studies. They are not equivalent to cosmetic ingredients or products intended for human testing. Their use should comply with applicable regulations, quality standards, and safety requirements. Additional product specifications, grades, and COA information can be retrieved from the Aladdin website using the product name, CAS number, or item number.

References

[1] National Center for Biotechnology Information. PubChem Compound Summary for CID 1110, Succinic Acid. PubChem. Accessed July 21, 2026.

[2] Wang Y, Kuo S, Shu M, et al. Staphylococcus epidermidis in the human skin microbiome mediates fermentation to inhibit the growth of Propionibacterium acnes: implications of probiotics in acne vulgaris. Appl Microbiol Biotechnol. 2014;98(1):411-424. doi:10.1007/s00253-013-5394-8.

[3] Fitz-Gibbon S, Tomida S, Chiu BH, et al. Propionibacterium acnes strain populations in the human skin microbiome associated with acne. J Invest Dermatol. 2013;133(9):2152-2160. doi:10.1038/jid.2013.21.

[4] Scholz CFP, Kilian M. The natural history of cutaneous propionibacteria, and reclassification of selected species within the genus Propionibacterium to the proposed novel genera Acidipropionibacterium, Cutibacterium and Pseudopropionibacterium. Int J Syst Evol Microbiol. 2016;66(11):4422-4432. doi:10.1099/ijsem.0.001367.

[5] Lambers H, Piessens S, Bloem A, Pronk H, Finkel P. Natural skin surface pH is on average below 5, which is beneficial for its resident flora. Int J Cosmet Sci. 2006;28(5):359-370. doi:10.1111/j.1467-2494.2006.00344.x.

[6] Hachem JP, Crumrine D, Fluhr J, et al. pH directly regulates epidermal permeability barrier homeostasis, and stratum corneum integrity/cohesion. J Invest Dermatol. 2003;121(2):345-353. doi:10.1046/j.1523-1747.2003.12365.x.

[7] Tannahill GM, Curtis AM, Adamik J, et al. Succinate is an inflammatory signal that induces interleukin-1β through hypoxia-inducible factor-1α. Nature. 2013;496(7444):238-242. doi:10.1038/nature11986.

[8] National Center for Biotechnology Information. PubChem Compound Summary for CID 338, Salicylic Acid. PubChem. Accessed July 21, 2026.

[9] Arif T. Salicylic acid as a peeling agent: a comprehensive review. Clin Cosmet Investig Dermatol. 2015;8:455-461. doi:10.2147/CCID.S84765.

[10] Liu H, Yu H, Xia J, Liu L, Liu GJ. Topical azelaic acid, salicylic acid, nicotinamide, sulphur, zinc and fruit acid (alpha-hydroxy acid) for acne. Cochrane Database Syst Rev. 2020;5(5):CD011368. doi:10.1002/14651858.CD011368.pub2.

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