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Facial acids – how they work and the differences between AHA, BHA, and PHA
Facial acids – how they work and the differences between AHA, BHA, and PHA
Acids used in professional skin therapy are among the most frequently selected methods for improving overall skin quality. In practice, however, many individuals do not fully understand how specific groups of acids differ or why one formulation delivers visible results while another may lead to irritation or no noticeable improvement.
Understanding the differences between AHA, BHA, and PHA allows you to design a treatment that is not only effective, but above all controlled, safe, and aligned with the skin’s actual condition.
If you want to explore a broader perspective on skin function and treatment planning, review other cosmetology courses, where skin processes and practical therapeutic approaches are discussed in detail.
How acids interact with the skin
The action of acids is not limited to “exfoliation.” This is a simplified view.
In reality, acids influence:
- intercellular cohesion within the stratum corneum
- epidermal turnover rate
- sebaceous gland activity
- inflammatory pathways in the skin
- hydration levels and the integrity of the skin barrier
The final outcome depends not only on the type of acid, but also on its concentration, pH level, and method of application.
AHA – water-soluble acids
Alpha hydroxy acids primarily act on the surface of the skin and within the epidermis.
Their mechanism involves loosening the bonds between corneocytes, the cells that form the outermost layer of the skin. This leads to controlled exfoliation and the gradual exposure of a smoother, more refined skin surface.
The most commonly used AHAs include:
- glycolic acid
- lactic acid
- mandelic acid
How AHA works
→ smooths skin texture
→ improves overall tone
→ enhances hydration levels
→ supports cellular renewal
→ reduces the appearance of fine lines
AHA performs best for:
- dry and dehydrated skin
- mature skin
- hyperpigmentation
- uneven skin texture
Important: the smaller the molecular size (for example glycolic acid), the deeper and more intensive the activity.
BHA – oil-soluble acids
Beta hydroxy acids function differently than AHA because they are oil-soluble.
This allows them to penetrate through sebum and reach the follicular canal.
In professional practice, the primary BHA used is:
- salicylic acid
How BHA works
→ decongests pores
→ dissolves excess sebum
→ provides anti-inflammatory support
→ reduces comedone formation
→ regulates oil production
BHA is particularly effective for:
- oily skin
- acne-prone conditions
- comedones
- enlarged pores
It is one of the few acids that works inside the pore, not only on the surface of the skin.
PHA – next-generation acids
Polyhydroxy acids represent a gentler alternative to AHA.
Due to their larger molecular structure:
→ they penetrate the skin more slowly
→ act more superficially
→ reduce the risk of irritation
The most commonly used PHAs include:
- lactobionic acid
- gluconolactone
How PHA works
→ provides gentle exfoliation
→ delivers intensive hydration
→ supports barrier function
→ offers antioxidant protection
→ improves overall skin comfort
PHA is especially recommended for:
- sensitive skin
- vascular or reactive skin
- compromised barrier conditions
- low tolerance to more aggressive exfoliation
It is an effective option for skin that does not tolerate more intensive acid-based treatments.
Key differences – AHA vs BHA vs PHA
The differences between AHA, BHA, and PHA are primarily defined by their solubility, depth of action, and interaction with specific skin structures. The comparison below highlights the most relevant clinical distinctions.
| Acid type | Primary action level | Skin indication | Key effects |
|---|---|---|---|
| AHA | surface epidermis | dry, mature | smoothing, hydration |
| BHA | within pores | oily, acne-prone | clarifying, oil control |
| PHA | very superficial | sensitive | repair, hydration |
Why one acid works and another does not
This is one of the most common challenges in acid-based treatments.
The outcome is not determined by the “name of the acid” alone.
Critical factors include:
- concentration
- formulation pH
- vehicle (alcohol, gel, emulsion)
- application time
- skin preparation
- treatment consistency
This is why the same acid can:
→ deliver highly effective results
→ or produce no visible improvement
Does a peel work after one treatment
Chemical peels deliver cumulative results.
This means:
→ each treatment enhances the previous one
→ the skin remodels progressively
→ visible improvement requires time and consistency
If you want to understand how to manage this type of therapy in practice, review the chemical peels course, where step-by-step treatment planning is demonstrated in a clinical setting.
Table – factors influencing peel intensity
| Factor | Impact on performance |
|---|---|
| acid concentration | higher = stronger activity |
| pH level | lower = deeper penetration |
| formulation type | alcohol = more aggressive, gel = milder |
| application time | longer = increased intensity |
| number of layers | more layers = deeper effect |
| skin preparation | improves efficacy and control |
FAQ – acids and chemical peels
Can acids be used year-round?
Yes, depending on the acid type and treatment protocol. Some acids such as PHA, azelaic, or ferulic can be used year-round with proper photoprotection. Stronger peels require more caution.
Do chemical peels hurt?
Sensations depend on the acid type and intensity. Most commonly, clients experience tingling, warmth, or mild stinging, which is controlled and temporary.
Why is there not always visible peeling after treatment?
Because exfoliation often occurs on a microscopic level. Lack of visible flaking does not mean lack of activity.
Which acid is best for acne?
Salicylic, azelaic, and pyruvic acids are commonly used. Selection depends on the type of acne and overall skin condition.
Can different acids be combined in one treatment?
Yes, combination protocols are widely used in professional practice, but they require advanced knowledge and parameter control.
How many treatments are needed to see results?
Peels work cumulatively. Initial improvements may appear quickly, but meaningful skin transformation develops over a treatment series.
Are acids safe for sensitive skin?
Yes, when the correct type is selected, such as PHA, mandelic, or lactic acid, and when parameters are properly adjusted.
What matters most in acid-based treatments
Acids are not a single procedure. They are a structured tool used in professional skin therapy.
AHA, BHA, and PHA differ in mechanism, penetration depth, and clinical application.
The correct selection should be based on:
→ actual skin condition
→ the concern being treated
→ skin tolerance
→ therapeutic goal
Only then does a peel move from a random procedure to a controlled and effective treatment element.
Want to explore a wider range of acids and learn how to work with them step by step? Review the chemical peels course and learn how to combine acids with other treatments in real clinical practice.
