Ingredient | Alpha-Hydroxy Acid
Lactic Acid (AHA)
INCI · Lactic Acid
Related names and forms: Sodium Lactate. This list does not indicate synonyms or exact ingredient matches.
Lactic acid (INCI: Lactic Acid) is an alpha-hydroxy acid in the AHA family with a larger molecule than glycolic acid. Its greater molecular weight means slower, more superficial penetration, so it is positioned as an AHA generally more comfortably tolerated by sensitive skin than glycolic acid. A second distinguishing feature is a mild moisture-retaining (humectant) aspect. It is related to lactate, a component of the skin's own natural moisturising factor (NMF), which is why its salt form (Sodium Lactate) is also used separately as a humectant in some formulas. As with all AHAs, its effect is shaped more by pH and the proportion of free acid than by percentage. The typical cosmetic range is 5%-10%; beyond that is professional peeling. It appears on labels as Lactic Acid and has a verified individual PubChem record (CID 612, C3H6O3). Klaris considers lactic acid alongside percentage, pH, format and companion actives.
i. Cosmetic Functions
Frequently Discussed Effects
The following headings summarise areas of effect frequently discussed in the literature; visible results in each area require regular use and a suitable formula.
Surface Turnover Support
Used in formulas that support dead cell turnover at the surface.
A Humectant Aspect
Unlike glycolic acid, it has a mild moisture-retaining (humectant) profile.
An AHA Closer to Sensitive Profiles
Its larger molecular weight helps provide a more context-sensitive option for sensitive skin.
Mechanism
What Happens Within the Skin?
The following points summarise mechanisms from dermocosmetic literature in plain English. Klaris presents them as background information to help readers understand the context, not as medical claims.
Step 1
A Medium-to-Large AHA Molecule
A larger molecular weight than glycolic acid means slower, more superficial penetration and a more comfortable profile for sensitive skin.
Step 2
An Additional Humectant Aspect
Unlike other AHAs, it has a mild humectant profile; lactate is also a component of NMF.
Step 3
pH and Free Acid
Its effect depends more on formula pH and the proportion of free acid than on percentage. The same percentage is considered differently at different pH levels.
Step 4
An AHA Closer to Sensitive Profiles
Its larger molecular weight helps offer a more context-appropriate option than glycolic acid for sensitive and dry profiles.
Step 5
Sun Sensitivity
AHA routines can make skin more sensitive to sunlight for a time, making daytime sun protection a consistent complement.
ii. Role in the Formula
How Is It Read on a Label?
Lactic acid is commonly used at 5% - 10% in cosmetic formulas; higher concentrations remain within professional peels. Changes in pH shape its effect: the same percentage gives different signals at different pH levels.
A Closer Look · pH, Stability, Synergy
Lactic acid is considered one of the AHAs closer to sensitive profiles for two reasons. First, molecular weight: being larger than glycolic acid means slower surface penetration and a more measured effect. Second, its humectant aspect: lactic acid and its salt, sodium lactate, are related to the skin's natural moisturising factor, so some formulas combine the appearance of surface renewal with moisture support. It remains an AHA, however: pH and the proportion of free acid determine its effect more than percentage, and the same percentage is more potent at low pH. The cosmetic form may commonly be racemic (DL) or L-(+) lactic acid. The INCI name Lactic Acid can cover both; in cosmetics, differences in behaviour are largely managed through formula pH and concentration. The cosmetic range is 5%-10%; beyond that is professional peeling. As AHAs can make skin more sensitive to sunlight for a time, daytime sun protection is a consistent complement. Gradual use is a measured approach with high-active combinations (AHA + BHA + retinoid). When assessing a lactic acid product, Klaris considers percentage, pH, format (leave-on or rinse-off) and companion actives as a whole.
Typical Concentration Range
5% - 10% (common in cosmetics)
Ingredient Family
Acids
iii. Sensitivity Advisory
A Note on Extra Care in Context
Considering sun protection separately can be a consistent choice with regular use. For sensitive and rosacea-prone skin, starting at a low concentration and observing the response may be helpful.
A sensitivity advisory is not an instruction for use; where individual health circumstances, pregnancy or known sensitivities are involved, discussing the decision with your doctor may be a more contextual approach.
Common Misconceptions
Frequently Confused Points
Common Belief
Lactic acid comes from milk and is the same as a dairy product.
A More Contextual Reading
Although its name shares a root with lactose and milk, cosmetic lactic acid is usually a defined molecule produced through fermentation or synthesis. It is not the same as applying milk.
Common Belief
Because it is an AHA, lactic acid is harsh and cannot be used on sensitive skin.
A More Contextual Reading
Its larger molecular weight and humectant aspect make lactic acid one of the AHAs considered closest to sensitive profiles. Suitability depends on percentage, pH and the whole formula.
Common Belief
Its humectant aspect makes pH unimportant.
A More Contextual Reading
Lactic acid is an AHA, and its surface-renewal context depends on pH and the proportion of free acid. Its humectant aspect does not change this: formula pH remains decisive.
Common Belief
It does not work because it is weaker than glycolic acid.
A More Contextual Reading
Slower, more superficial action is not weakness but a different context. For sensitive and dry profiles, that more measured approach is often a more suitable choice.
Scientific Basis
Sources and Their Scope
The following headings indicate areas of research; they are not citations of a specific publication or confirmation that every statement on this page has been verified. The links provided should be read with their individual scope in mind.
- International INCI / CosIng database
- Dermocosmetic research publications
- Formulation chemistry guides
Source Links
- Database RecordPubChem | Lactic Acid Ingredient Record (CID 612)
Database records provide ingredient identity and registration information; on their own, they do not establish the effect of a finished product or its suitability for a profile. Search links are not specific research papers.
v. Acids Family
Other Ingredients in the Same Family
Explore ingredients in the same functional family to deepen your reading of formulas.
vi. Academy · Related Reading
For a Closer Look
vii. Related Concern Guides
Guides That Include This Ingredient
Klaris · Example Analyses
How Does Lactic Acid (AHA) Feature
in Your Products?
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