ABSTRACT
Introduction 442
Materials and Methods 443
Sources of Materials 443
Stability of Test Materials in Products 443
Human Studies 443
Back Cumulative Irritation Test 15,16) 443
Facial Irritation Test 1 444
Facial Irritation Test 2 444
Facial Benefits Study 1 445
Facial Benefits Study 2 447
Retinoid Photostability 447
Cell Culture 447
Results 447
Back Cumulative Irritation Test 447
Facial Irritation Test 1 448
Facial Benefits Study 1 450
Retinoid Photostability 455
Facial Irritation Test 2 456
Facial Benefits Study 2 456
Inhibition of Dermal GAG Production 458
Discussion 459
Acknowledgments 461
References 461
INTRODUCTION
Topical trans-retinoic acid (t-RA) is well known for its activity in improving the
appearance of the signs of skin photodamage such as fine lines, wrinkles, and pig-
mentation problems (1,2). Although t-RA provides skin benefits, it can also
produce aesthetic negatives such as irritation and dryness (3). To minimize
these unwanted side effects and yet still deliver benefits, t-RA precursors such
as retinol (3) and retinaldehyde (4) and retinyl esters such as retinyl acetate (5)
and retinyl palmitate (6) have been used widely in the skin care industry.
Although these agents may improve the activity-to-irritation ratio, at least
the former three can still have substantial aesthetic issues. The fourth, retinyl
palmitate, has an overall weak activity profile (7).
