Glycolic vs Lactic vs Mandelic: AHA Comparison with Evidence

Alpha-hydroxy acids (AHAs) are among the most effective exfoliating ingredients available, but they’re not interchangeable. Each AHA has distinct properties that make it suited for different skin types and concerns. Understanding the differences helps you choose the right acid for your skin.

What AHAs Do

All AHAs work by:

• Breaking the bonds between dead skin cells
• Accelerating cellular turnover
• Promoting shedding of the stratum corneum
• Revealing fresher skin beneath
• Stimulating collagen production over time

The differences lie in molecular size, penetration depth, and additional properties.

The Basics

• Source: Derived from sugar cane
• Molecular weight: 76 Daltons (smallest AHA)
• Penetration: Deepest of the common AHAs

How It Works

Glycolic acid’s small molecular size allows it to penetrate the stratum corneum more readily than larger AHAs. This means:

• Faster, more dramatic results
• Greater efficacy at lower concentrations
• More potential for irritation

Best For

• Sun damage and photoageing: The deeper penetration helps with pigmentation and fine lines
• Dull, rough texture: Effective surface renewal
• Acne scarring: Helps with surface texture improvement
• Those who tolerate acids well: Not for sensitive skin

Concentrations

• 5-10%: Daily use products
• 20-30%: Professional strength at-home treatments
• 50-70%: Professional peels only

Considerations

• Most irritating of the common AHAs
• Can cause significant sensitivity in reactive skin types
• Requires careful sun protection (increased photosensitivity)
• Not ideal for beginners or those with compromised barriers

Evidence

Glycolic acid has the most extensive research of any AHA. Studies demonstrate improvements in photoageing, texture, and pigmentation at various concentrations.

The Basics

• Source: Derived from milk (though now typically synthesised)
• Molecular weight: 90 Daltons (larger than glycolic)
• Penetration: More superficial than glycolic acid

How It Works

Lactic acid’s larger molecular size means it works more gradually and superficially. But it has an additional benefit: it’s also a humectant.

The hydrating property comes from lactic acid’s ability to attract and hold water, providing both exfoliation and moisture retention.

Best For

• Dry skin: Exfoliates without stripping moisture
• Sensitive skin: Generally better tolerated than glycolic
• First-time acid users: Gentler introduction to AHAs
• Hyperpigmentation: Effective for pigmentation with less irritation
• Mature skin: Addresses texture and dryness together

Concentrations

• 5-10%: Daily use
• 10-15%: Regular treatments
• Higher concentrations: Professional use

Considerations

• Slower results than glycolic acid
• May require higher concentrations for equivalent effect
• The “milk” origin is mostly historical — modern lactic acid is typically synthesised
• Still causes photosensitivity (use sunscreen)

Evidence

Research supports lactic acid for photoageing, hyperpigmentation, and improving skin hydration. Some studies suggest it’s as effective as glycolic acid with less irritation.

The Basics

• Source: Derived from bitter almonds
• Molecular weight: 152 Daltons (largest common AHA)
• Penetration: Most superficial, slowest absorption

How It Works

Mandelic acid’s large molecular size means it penetrates slowly and stays in the upper layers of skin longer. This slow, even penetration reduces irritation risk.

Additionally, mandelic acid has:

• Antibacterial properties: Helps with acne
• Oil solubility: Unusual for an AHA, giving it some BHA-like pore-penetrating ability

Best For

• Acne-prone skin: The antibacterial action and mild oil solubility help
• Darker skin tones: Less risk of post-inflammatory hyperpigmentation
• Rosacea-prone skin: Often tolerated when other acids aren’t
• Sensitive skin: The gentlest AHA option
• Beginners: Low risk introduction to acid exfoliation

Concentrations

• 5-10%: Daily use
• 10-20%: Regular treatments
• 20-40%: Professional peels

Considerations

• Slowest results — patience required
• May need higher concentrations than glycolic for equivalent exfoliation
• Less researched than glycolic or lactic acid
• Still requires sun protection

Evidence

Research on mandelic acid is less extensive than glycolic or lactic, but available studies support efficacy for acne, pigmentation, and photoageing with good tolerability profiles.

Quick Comparison Table

Property	Glycolic	Lactic	Mandelic
Molecular size	Smallest (76)	Medium (90)	Largest (152)
Penetration	Deepest	Moderate	Superficial
Intensity	Strongest	Moderate	Gentlest
Hydrating	No	Yes	No
Antibacterial	Minimal	Minimal	Yes
Oil solubility	No	No	Partial
Best for	Photoageing, texture	Dry skin, beginners	Sensitive/acne-prone
Irritation risk	Highest	Moderate	Lowest

Start with Mandelic or Lactic if:

• You’ve never used acids before
• Your skin is sensitive or reactive
• You have rosacea
• You have a darker skin tone (PIH risk)
• You want gentle, gradual results
• You’re already using other actives (retinoids, etc.)

Move to Glycolic if:

• Your skin tolerates other acids well
• You want faster, more dramatic results
• You’re addressing significant sun damage
• Your barrier is strong and healthy
• You don’t have sensitivity issues

Consider Mandelic specifically if:

• You have acne alongside other concerns
• Other AHAs have caused irritation
• You want the gentlest possible option

Frequency

Starting: 2-3 times per week Building up: Daily if tolerated Maintenance: Adjust based on skin response

Application

Apply to clean, dry skin. Allow to absorb before applying subsequent products. Can be used AM or PM, but evening is often preferred to avoid layering under sunscreen.

Sun Protection

All AHAs increase photosensitivity. Daily SPF 30+ is essential when using any AHA.

Combining AHAs

Using different AHAs at different times can provide benefits of each. For example, lactic acid for daily maintenance, occasional mandelic acid treatment for acne, periodic glycolic acid for deeper exfoliation.

Over-exfoliation

More isn’t better. Signs of over-exfoliation:

• Persistent redness
• Unusual sensitivity
• Tight, shiny skin
• Increased breakouts

If these occur, stop AHAs and focus on barrier repair.

Combining Too Many Actives

Using AHAs with retinoids, BHAs, and vitamin C simultaneously can overwhelm skin. Build routines gradually and don’t combine all actives at once.

Ignoring Sun Protection

AHAs without sunscreen can worsen the problems you’re trying to treat. Non-negotiable.

Expecting Immediate Results

Cellular turnover takes time. Expect 4-8 weeks for visible improvement, with continued benefits over months.

The Bottom Line

There’s no “best” AHA — there’s the right AHA for your skin:

• Glycolic for maximum efficacy when tolerated
• Lactic for hydration plus exfoliation
• Mandelic for sensitive skin and acne concerns

Start gentler than you think you need, build gradually, protect from the sun, and give products time to work. Chemical exfoliation is a marathon, not a sprint.