What Is PHA (Polyhydroxy Acid)? Difference from AHA and Sensitive Skin

PHA can be thought of as a larger, more water-loving version of the same basic chemistry as AHA. Its many hydroxyl groups attract water, and its size is thought to slow passage into the upper layer. In marketing it is called "next-generation AHA". The difference measured on skin is real but not as large as claimed, and it can come with a loss of strength.

How do gluconolactone and lactobionic acid differ?

You will not see the term "PHA" on the label; you look for the names of the molecules. The two most common names in the family do not do the same job. Lactobionic acid is a combination of a sugar and gluconic acid, so technically it belongs to the aldobionic acid (bionic acid) class, but in practice it is discussed within PHAs.

How much does the PHA versus AHA difference come out when measured?

In one known comparison, gluconolactone products were tested side by side with glycolic acid products for 12 weeks. Both groups showed a significant improvement in the appearance of ageing. In two measurements, AHA was ahead: on dullness, 17,1% versus 12,4%, and on skin elasticity and recovery, 13,5% versus 10,2%. Where PHA came out ahead was tolerance: stinging and irritation at weeks 6 and 12 were significantly higher in the AHA group.

Among this study's authors are researchers from a company that develops these ingredients, so independent replication is needed. A balanced reading: a little less effect, noticeably less discomfort. If your skin cannot tolerate AHA, this trade-off makes sense. If it tolerates it without problems, there is no strong reason to switch to PHA.

Is there really no sun sensitivity?

This is the most frequently heard promise of PHA, but its basis is narrow. In a study dated 2004, gluconolactone provided up to 50% protection against UV-triggered activation of the elastin gene in a laboratory model, and in human skin it did not significantly increase sunburn cells. Lactobionic acid lacks data of the same clarity. The one-week sun warning recommended for AHAs does not name PHAs, but that does not mean "no sunscreen needed". While using an exfoliating product, keep applying a broad-spectrum sunscreen of at least SPF 30; outdoors, renew it every 2 hours and after sweating or swimming.

How much data exists for sensitive, red or acne-prone skin?

• Acne: In a double-blind study of 150 people, 14% gluconolactone and 5% benzoyl peroxide reduced lesions; gluconolactone caused fewer side effects. This study is dated 1992, so it is old.
• Rosacea redness: In a matched study of 200 people with mild redness, 30-day use of a 5% gluconolactone serum was compared with a single session of intense pulsed light. Light therapy was superior for redness and overall appearance, while pore and tone results remained similar. So it does not replace a treatment. If the redness persists, see a dermatologist about the possibility of rosacea.
• Skin pH: A moisturiser with 10% lactobionic acid lowered the surface pH of the skin in laboratory and volunteer tests, without causing significant irritation or barrier impairment.
• Concentration: In small half-face studies (10-16 people), both gluconolactone and lactobionic acid increased moisture similarly at 10% and 30%. A higher concentration has not been shown to give additional benefit here.
• By age: In a comparison of 40% lactobionic and 40% mandelic acid peels, moisture increased only with lactobionic acid in the 50-60 age group, while in the 30-40 age group both acids increased moisture.

What is missing are large, independent, controlled studies in people diagnosed with sensitive skin. The claim "suitable for sensitive skin" currently rests more on stinging comparisons and molecular size.

How does PHA fit into a routine, and what is its limit?

The EU cosmetics regulation's restricted substances annexes have no separate entry for gluconolactone and lactobionic acid. The 10% and pH 3,5 framework used for AHAs was not built for these molecules, so it is hard to state a reliable "home product ceiling". Since there is no firm protocol, the following are example starting points:

1. Test for 7-10 days on the inner arm or elbow crease, applied twice a day. Being a PHA does not mean it will not irritate.
2. Apply a thin layer 2-3 evenings a week, then add a moisturiser on top.
3. Do not start on the same evening as a retinoid, peel or another acid. The peel article can guide you on frequency.
4. If you are targeting the appearance of ageing, wait at least 6 weeks; studies have run for 12 weeks.
5. Do not use during an eczema flare, on an open wound, or on sunburn. During pregnancy and breastfeeding, ask your doctor first.