How to use acidic skin care products without causing pitfalls? Full analysis of AHA, BHA, PHAs

"Using acids" has become the only way for many people to improve their skin care - fruit acid peels, salicylic acid acne removal, A acid anti-aging... However, if acid products are not used properly, they will cause excessive exfoliation and irritate the barrier. Only when they are used properly can pores, skin color, and acne be truly improved. This article explains these types of acids clearly from a scientific perspective.

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AHA (Alpha Hydroxy Acid / Fruit Acid)

Common types

Species	Molecular weight	Main sources	Characteristics
Glycolic acid (glycolic acid)	smallest	sugar cane	most penetrating, fastest-acting, and most irritating
Lactic acid	Smaller	Milk	It also has a moisturizing effect and is relatively mild in irritation
Malic acid	Medium	Apple	Mild effect, rarely used alone in high concentrations
Citric Acid	Larger	Citrus	More commonly used as a pH adjuster rather than a workhorse acid
Tartaric acid	Larger	Grapes	Similar, mostly supporting roles

Principle of action

AHA acts on the surface of the skin, breaking the adhesions between keratinocytes (loosening the glue of glycosaminoglycans), accelerating the shedding of dead skin cells and the upward movement of new cells.

Suitable question:

• Dull, sallow complexion -Dry fine lines
• Post-sun stains and sun damage
• Enlarged pores (caused by accumulation of cutin on the surface)

Concentration Reference:

• 5–8%: Mild for entry, no adjustment required for daily use
• 8–15%: Moderate, recommended to start with low frequency (2–3 times per week)
• 15–30%: Skin rejuvenation level, experience is required
• 30% or more: Professional chemical peel, not recommended for self-use

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BHA (Beta Hydroxy Acid/Salicylic Acid)

Salicylic acid is the most common representation of BHA (almost synonymous with BHA).

The biggest difference with AHA

Salicylic acid is fat-soluble and AHA is water-soluble.

This difference determines:

• Salicylic acid can penetrate into the sebum (oil) inside the pores to work
• AHA mainly acts on the surface layer

Suitable question:

• Acne, blackheads, whiteheads (keratin plugs in pores)
• Acne (suppresses excessive secretion of sebaceous glands)
• Pore clogging problem for oily and combination skin

Concentration Reference:

• 0.5–1%: very mild, suitable for sensitive skin at the beginning
• 1–2%: Concentration for regular skin care products, mainstream serums and toners
• 2%: upper limit (domestic regulations limit salicylic acid in popular skin care products to ≤ 2%)

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PHA (Polyhydroxy Acid): The mildest option among acids

PHA has a much larger molecular weight than AHA, has a slower penetration rate, and is less irritating.

Common types: Gluconolactone (GLA), lactobionic acid

Features:

• The effect is also to promote keratin metabolism, but it is more gentle
• Has antioxidant and moisturizing effects at the same time
• Suitable for sensitive skin and skin with damaged barrier
• Not suitable for people who want "quick results"

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A acid (retinoic acid): not included in the category of acids, but often confused

Strictly speaking, retinoic acid (retinoic acid) is not an "acid" in the AHA/BHA framework. It works on a completely different principle - it affects gene expression by binding to cell nuclear receptors, promoting collagen synthesis and cell renewal.

DIFFERENCE:

• AHA/BHA/PHA: Physically remove dead skin and promote keratin metabolism
• A acid: biological regulation, affecting cell differentiation, medical grade anti-aging

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Use the principle of order and superposition

pH is key:

AHA and BHA require an acidic environment (pH 3–4) to effectively exfoliate.

Common Error Overlay:

• Use products containing niacinamide immediately after using up AHA/BHA → It’s okay when both are at a lower pH, but if the niacinamide product has a higher pH, it will neutralize the effect of the acid
• Use AHA + BHA + A alcohol in the same morning and evening → superimposed irritation and excessive exfoliation

Recommended Steps:

1. Cleansing
2. Toner (acid-containing product) or acid-containing serum (leave on for 15–20 minutes)
3. Other essences (moisturizing, antioxidant)
4. Lotion/Cream

Early/Late Assignment:

• AHA/BHA recommends use at night (photosensitivity, sun protection must be used during the day after use)
• Use sun protection (SPF 30+ or above) during morning skin care steps

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How to tell if acid can be used on your skin

Signals to start trying:

• The skin barrier is relatively healthy (no obvious redness, tightness, or peeling)
• Has been used stably for more than 3 months with regular skin care
• No obvious intolerance to basic ingredients (moisturizer, sunscreen)

Not suitable for acid use:

• Acne in the acute stage (massive inflammatory pustules) → anti-inflammatory first
• Skin wounds or damage
• Barrier impairment (persistent stinging, redness)
• Are using high concentrations of A-alcohol/A-acid (superimposed stimulation is too strong)

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Common side effects and treatments

Symptoms	Causes	Treatment
Slight stinging after use	Normal, related to low pH	Shorten the action time, or apply a thin layer of moisturizing water to dilute it first
Persistent redness and burning sensation	The concentration is too high or the frequency is too high	Pause to restore barrier
Extensive peeling	Excessive exfoliation	Stop using and rebuild the barrier (ceramide + hyaluronic acid)
On the contrary, acne increases	The initial "acne breakout" is normal (keratin metabolism is accelerated, and the blocked acne is pushed out)	Continue to use it for 1 month and re-evaluate

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*This article technically refers to Paula's Choice cosmetic ingredient database and dermatology literature, and does not represent a recommendation for a specific brand. When using acid products, please adjust according to your personal skin type. *