The K-beauty approach to exfoliation that doesn't destroy the barrier — and why gentler acids win long-term

AHA vs BHA vs PHA: understanding why the third generation was developed

Alpha-hydroxy acids (AHAs, primarily glycolic and lactic acid) exfoliate by cleaving the bonds between corneocytes in the stratum corneum, producing smooth skin but also disrupting tight junctions and temporarily reducing barrier integrity. Beta-hydroxy acids (BHAs, primarily salicylic acid) penetrate into pores and dissolve sebum-bound dead cells, making them effective for oily and congestion-prone skin. Polyhydroxy acids (PHAs — gluconolactone, lactobionic acid, galactose) achieve similar exfoliation via a larger molecular size that limits penetration to the outermost cell layers, reducing irritation potential to near zero. PHAs also have documented humectant and antioxidant activity that AHAs and BHAs do not share, making them genuinely gentle rather than simply diluted.

Guava extract as a natural PHA-delivery vehicle in K-beauty formulation

Guava (Psidium guajava) extract is used in K-beauty formulations as a botanical source of natural PHAs, particularly gluconolactone and related compounds. Beyond its PHA content, guava extract provides high-concentration vitamin C (guava contains more vitamin C per gram than citrus), quercetin (a flavonoid antioxidant) and ellagic acid (an inhibitor of melanin production). The combination of gentle exfoliation, vitamin C brightening and antioxidant activity in a single botanical extract explains why guava has become a signature ingredient in K-beauty formulas targeting texture improvement and brightening simultaneously, without the irritation profile of synthetic acid combinations.

Building a sustainable exfoliation protocol around PHAs for sensitive and barrier-compromised skin

For sensitive, reactive or barrier-compromised skin, PHAs are the sustainable long-term exfoliation choice. Protocol: apply PHA serum two to three evenings per week after cleansing and before moisturiser. Do not combine with AHA or retinoid on the same night (though PHAs are compatible with niacinamide, hyaluronic acid and ceramides). Allow three to four weeks of consistent use to see measurable texture improvement — PHAs work more gradually than AHAs but produce steadily improving results without the rebound sensitivity that aggressive AHA use causes. Morning after any exfoliation step: always apply SPF, as any form of chemical exfoliation increases UV sensitivity.

BENTON Guava 70 Skin Toner Face Mask Pad 70ea — available on BuyBeautyKorea →