Reference Guide for the pH Setting of Cosmetics

Outline

Setting cosmetic pH values requires balancing skin physiology, regulatory frameworks, and formulation science. For cosmetic manufacturers, obtaining pH-compatible raw materials—whether buffers, stabilizers, or actives—enables brands to create safer, high-performance products. By prioritizing pH alignment with skin's natural state and product functionality, Alfa Chemistry empowers innovators to meet evolving market demands while adhering to global standards.

What Is pH?

pH or "hydrogen potential" measures the hydrogen concentration present in water. The pH value reveals whether an aqueous solution is acidic or alkaline by comparing it to distilled water which maintains a neutral pH of 7 within the 1 to 14 range. The measurement of pH applies only to aqueous solutions because oils lack this property.

Water-based liquids that measure below 7.0 on the pH scale are acidic whereas water-based liquids that measure above 7.0 on the pH scale are considered to be alkaline or basic. Acids typically taste sour while bases demonstrate a bitter flavor.

Typically, lemon juice demonstrates acidity through its composition of about 5% citric acid and its pH measurement of 2.2. Baking soda possesses a bitter taste and registers a pH level of 9.

Skin Physiology and pH Balance

Human skin maintains a natural acidic mantle, with a pH range of 4.5–6.5 (averaging ~5.5), which supports barrier function, enzyme activity, and microbial balance. Key functions include:

• Barrier Protection: The acidic environment stabilizes the stratum corneum, enhances lipid organization, and reduces transepidermal water loss.
• Microbiome Regulation: A pH of ~5.5 inhibits pathogenic bacteria (e.g., S. aureus) while promoting beneficial flora like C. acnes.
• Enzyme Activity: Proteases and lipid-processing enzymes function optimally at pH 5.5; deviations impair desquamation and repair.

Makeup products that disturb this equilibrium can result in dry skin and irritation while weakening skin defenses. Thus, aligning product pH with skin's natural range is ideal, especially for sensitive or infant skin.

Skin pH affected by a variety of factors. [1]

Common pH Ranges for Major Skincare Product Categories

Consumer Trends and pH Optimization

Skin Age and pH

Skin pH changes with age, becoming more alkaline over time and more susceptible to conditions such as wrinkles, pigmentation, and acne. Moderately aged skin (>55 years) also shows permeability barrier defects and altered integrity, along with an increased pH.

Young men have higher skin moisture levels than women of the same age. Men's skin hydration levels begin to decline after reaching 40 years old whereas women maintain stable or even increase hydration levels throughout their lives. Men maintain a stable and high level of skin sebum production as they age while women see a gradual decrease in sebum production over their lifetime. Typically, men exhibit lower pH levels compared to women.

pH of Hair

In cosmetics, "pH neutral" means something slightly different. Skin and hair products labeled "pH neutral" are most likely not pH 7 neutral. Cosmetics labeled "pH neutral" have a pH close to the pH of your skin or hair.

• Shiny hair: pH 4.2 to 5.5
• Dull hair: pH > 7

Formulation-Driven pH Requirements

A. Ingredient Compatibility

• Thickeners: Carbomers require neutralization (pH 5–9) for viscosity; specific grades narrow this to 6.5–7.
• Preservatives: Organic acids (e.g., benzoic acid) lose efficacy above pH 6 due to ionization, while parabens hydrolyze in alkaline conditions.
• Actives: Vitamin C (ascorbic acid) stabilizes at pH<4; unstable above this range, necessitating acidic bases.

B. Product Category Variations

• Cleansers:
  a) Soap-based: pH 9–10 (traditional) vs. modern soap-based systems adjusted to pH<9.
  b) Amino Acid Surfactants: pH 6–7 optimizes foaming and mildness.
• Emulsions/Serums: Neutral pH (5–7) suits most hydrating products, balancing stability and skin compatibility.

Regulatory Standards and Safety Guidelines

Global regulations provide broad pH limits but emphasize tailored adjustments based on product type and target demographics:

• General Cosmetics: Products containing α-hydroxy acids (AHAs) should have a pH of ≥ 3.5. The pH value of products containing alkaline ingredients should be ≤11.
• Children's Products:
  a) Leave-on (e.g., lotions): pH 4.5–7.5
  b) Rinse-off (e.g., cleansers): pH 4.5–8.5

Exceptions require scientific justification and safety assessments.

• Anti-Aging/Exfoliants: Low-pH formulations (pH 3.5–4) enhance AHA efficacy but demand caution to avoid irritation.

Regulatory flexibility allows brands to refine ranges based on ingredient synergy and consumer needs while ensuring compliance. Of course, regulatory restrictions vary from country to country. For example, the US cosmetics pH standard is jointly formulated by the Food and Drug Administration safety regulations, state chemical bans and industry best practices. According to EU Cosmetics Regulation (EC) No 1223/2009, cosmetics products must fall within approved pH levels. In China, the quality control indicators in the "Cosmetic Safety Technical Specifications" and "Technical Guidelines for Children's Cosmetics" should be followed.

Please consult Alfa Chemistry's expert team for the latest regulatory standard information and recommendations.

pH Testing and Quality Control

• The direct measurement method is suitable for direct determination of the pH value of cosmetics (using a calibrated pH meter). This method is not suitable for powder, oil-based and water-in-oil emulsion cosmetics.
• The dilution method dilutes the sample ten times and then uses a calibrated pH meter for determination. If the product has a high oil content, it can be heated to 70℃-80℃, cooled and removed for use; powdered products can be filtered and precipitated for use.
• Measurement method of water-in-oil cosmetics: After the emulsification type of creams and lotions is identified, it is confirmed that they are water-in-oil cosmetics. They need to be demulsified by physical or chemical methods, diluted to obtain the tested solution, and then measured by pH meter.
• Stability Testing: Monitor pH shifts during storage, especially in formulations with reactive ingredients (e.g., AHAs, antioxidants).

Product Recommendations: pH-Related Ingredient Selection Guide

Reference

1. Milica Lukić, et al. Cosmetics, 2021, 8(3), 69.

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Reference Guide for the pH Setting of Cosmetics

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