Formulating with Acids: What Every Cosmetic Chemist Should Know

Acids are some of the most powerful and popular ingredients in skincare. Whether you're designing a gentle exfoliating serum or a high-performance peel, working with acids like glycolic, lactic, or salicylic acid requires careful consideration. From pH balance to ingredient compatibility, we’ll walk you through the essentials of formulating with acids for safe, effective, and stable results.

Acids play a wide range of roles in cosmetic formulations, from exfoliation and brightening to reducing inflammation and refining skin texture. Choosing the right acid depends on your product goals, skin type compatibility, and the formula’s overall design. Here’s a breakdown of the most commonly used cosmetic acids and their functions:

AHAs are water-soluble acids that work on the surface of the skin to promote exfoliation and improve skin texture.

• Examples: Glycolic Acid, Lactic Acid, Mandelic Acid
• Best for: Dull, dry, or aging skin
• Use level & considerations: Often used between 1–10%. Glycolic is the most potent and requires careful pH control; lactic and mandelic acids are gentler options.

BHAs are oil-soluble and penetrate deeper into the pores, making them excellent for treating acne and oily skin types.

• Example: Salicylic Acid
• Best for: Congested, acne-prone, or oily skin
• Use level & considerations: Typically used at 0.5–2%. Salicylic Acid needs a suitable solvent like ethanol or propylene glycol unless using an encapsulated form.

PHAs are a newer class of exfoliants that provide similar benefits to AHAs but are gentler due to their larger molecular size.

• Examples: Gluconolactone, Lactobionic Acid
• Best for: Sensitive skin or barrier-compromised skin
• Use level & considerations: Often used at 2–10%. Offer mild exfoliation along with hydration and antioxidant benefits.

• Azelaic Acid: Offers antibacterial, anti-inflammatory, and skin-brightening properties. Suitable for rosacea and acne-prone skin.
• Tranexamic Acid: A popular brightening ingredient that targets hyperpigmentation and redness without exfoliation.
• Ferulic Acid: An antioxidant often used to stabilize vitamins C and E, making it ideal for anti-aging and brightening formulas.
• Hyaluronic Acid: Technically not an exfoliating acid. It’s a hydrating molecule that pairs well with exfoliating acids to prevent dryness and irritation.

When formulating with acids, maintaining the correct pH is critical for both efficacy and skin safety. Most exfoliating acids, such as AHAs and BHAs, are most effective within a pH range of 3 to 4. Outside this range, their activity can be compromised, and skin irritation risks may increase.

• If the pH is too low (below ~3), the formula may become too harsh for the skin, increasing the risk of irritation or barrier disruption. Additionally, it may impact the stability of other ingredients in the formula.
• If the pH is too high (above ~4.5–5), exfoliating acids like glycolic or lactic acid lose their potency and may become ineffective as actives.

That’s why it’s essential to:

• Measure the final pH of the formulation once all ingredients are combined.
• Use buffering agents or neutralizers (like sodium hydroxide or triethanolamine) to adjust pH if needed.
• Consider pH compatibility when selecting additional ingredients such as thickeners, preservatives, and solubilizers.

A stable, well-balanced pH ensures your acid-based product performs as intended, delivering safe, visible results.

When working with acids in cosmetic formulations, it’s important to consider how they interact with other ingredients both from a stability and efficacy standpoint. Acids can be powerful actives, but they’re also sensitive to formulation context.

Some ingredients may become unstable or ineffective in acidic environments:

• Peptides can break down in low pH, losing their structure and function.
• Retinol (Vitamin A) and ascorbic acid (Vitamin C) are sensitive to pH and can become destabilized or cause increased irritation when combined with exfoliating acids.
• Highly active botanical extracts may be too harsh when combined with strong acids, potentially increasing irritation or disrupting the skin barrier.

If you’re formulating with these combinations, it’s essential to run stability and efficacy tests to ensure the final product performs safely and as intended.

Acidic environments can impact preservative performance and may increase the risk of metal ion interference.

• Opt for chelators like EDTA or phytic acid to bind metal ions and improve stability.
• Choose preservatives proven to be effective in low-pH systems, such as phenoxyethanol or benzoic acid derivatives.

Not all acids are water-soluble.

• Salicylic Acid, for example, requires a co-solvent such as ethanol, propylene glycol, or butylene glycol for proper solubilization unless you’re using a pre-solubilized or encapsulated version.
  Always confirm solubility early in the formulation process to avoid crystallization or layering in the final product.

Pairing acids with the right supporting ingredients can enhance performance, improve skin tolerance, and deliver a better overall user experience. Whether you’re formulating a gentle daily exfoliant or a high-strength peel, incorporating soothing, hydrating, and barrier-repairing components is key.

Ingredients like glycerin and hyaluronic acid help attract and retain moisture, counteracting the potential drying effects of exfoliating acids. They also support skin plumpness and comfort, especially in leave-on formulas.

To minimize irritation, it's smart to include skin-calming ingredients:

• Panthenol (Vitamin B5) – Hydrating and anti-inflammatory
• Allantoin – Promotes healing and reduces redness
• Bisabolol – A natural anti-irritant derived from chamomile

These ingredients can make acid-based products more suitable for sensitive skin or first-time users.

Acids can compromise the skin barrier if not properly buffered with replenishing lipids. Adding ingredients like:

• Ceramides
• Squalane
• Fatty alcohols or oils

…helps maintain barrier integrity and reduce transepidermal water loss (TEWL).

Film-forming agents help create a controlled delivery system and reduce the risk of irritation by slowing acid penetration. They can also enhance skin feel and spreadability.

Formulators might consider ingredients like:

• Silicones or silicone alternatives
• Polymers like polyquaterniums or acrylates

By building your formulation with these synergistic components, you can create acid products that are both effective and skin-friendly.

Acids are powerful tools in a formulator’s kit, offering benefits from exfoliation and brightening to acne care and skin renewal. But with that power comes responsibility. Understanding each acid’s properties, respecting pH requirements, and building balanced formulas with soothing, hydrating, and stabilizing ingredients is key to creating effective and skin-friendly products.