.
Study Site: Independent Testing Laboratory,
Philadelphia, Pennsylvania

The objective of the study was to determine whether daily treatment with topical AHA and PHA products alters the sensitivity of normal human skin to UVB radiation. A change in UV sensitivity resulting from enhanced transmission or, mitigation of the deleterious effects of UVB can be monitored by the formation of sunburn cells (SBCs).

Method: The study was conducted at a single center utilizing a complete block design. A total of ten subjects completed the study; there were eight males and two females ranging in age from 19 to 22 years. Nine subjects were skin type III and one subject was skin type II. Test products were blinded and applied once daily to the mid-back region under supervision at the laboratory, six times a week for four weeks. Topical applications were randomized among the test sites and applied using 1cc disposable plastic tuberculin syringes. The topical daily dose of each product was 100mg per test area (~2mg/cm2). The test products were thoroughly rubbed into the designated site using a finger cot.

Test Products

• 8% Glycolic Acid Cream (pH 4.08)
• 8% Gluconolactone Cream (pH 4.24)
• Untreated, Irradiated Control

Minimal Erythema Dose (MED) Determination: At the end of the study, the MED was determined in each of the test sites by exposing several skin sites (1cm in diameter) to a series of exposures in 25% dose increments from the solar simulator. The MED was defined as the time of exposure required to produce minimally perceptible erythema 20±4 hours after exposure.

Biopsies: Approximately 15 minutes after the last topical application of the test products, a circular area measuring 1cm in diameter within each test site was exposed once to a single dose of 1.5 times the MED as determined in the normal untreated skin site using the solar simulator. A similar exposure to 1.5 MEDs was given to the untreated normal skin site (control site). After 20±4 hours, a shave biopsy (~4x4mm) was obtained from each irradiated site following injection of a local anesthetic (xylocaine). The skin specimens were immediately fixed in 10% buffered formalin.

Histology: The fixed specimens were processed routinely, embedded in paraffin and then sectioned and stained with hematoxylin-eosin. The numbers of SBCs were determined in at least 12 sections at 50µ intervals. A minimum of 70 high power fields (HPFs) was counted from each biopsy and the average number of SBCs per HPF determined.

Results: The difference in the numbers of SBCs and the MEDs was evaluated using analysis of variance (ANOVA) with contrasts (protected t-test) to compare the various treatments.

MEDs: AHA and PHA treatment reduced the average MED compared to untreated as follows: glycolic acid by 17% (p<0.01) and gluconolactone by 8% (not 
significant) compared to the untreated control. Six of the ten subjects treated with gluconolactone did not experience a change in their MED value as seen in the table below.

MEDs
Percent Difference from Untreated

SBCs: There was an increase in the average number of SBCs per High Power Field (HPF) in the glycolic acid treated sites compared to untreated (p<0.05). Test sites treated with gluconolactone were not significantly different from untreated.

Conclusion: Glycolic acid caused an increase in sensitivity to solar simulated radiation as expected based on other studies. No photosensitizing effect was observed following treatment with product gluconolactone, the polyhydroxy acid.

Poster Presentation: American Academy of Dermatology Poster Exhibit: New Orleans, February 2002.