OXYHEMOGLOBIN IS A QUANTIFIABLE MEASURE OF EXPERIMENTALLY-INDUCED CHRONIC TRETINOIN INFLAMMATION AND ACCOMMODATION IN PHOTODAMAGED SKIN

Chronic exposure to a weak irritant leads to inflammatory changes whic h may be followed by pigmentary changes and accommodation. The inflamm atory responses to acute exposure to an irritant have been extensively studied. This study investigated quantitatively the inflammatory reac tions produced in photodamaged skin with chronic application of a weak chemical irritant (tretinoin cream 0.025%) over a period of 9 months (36 weeks). Forty-eight subjects with moderately to severely photodama ged skin were enrolled in a 36-week, double-blind placebo-controlled s tudy. Tretinoin cream was applied nightly on the distal two thirds of one dorsal forearm and placebo on the other. The proximal third of eac h dorsal forearm received no treatment and served as control. Clinical assessments and diffuse reflectance measurements were made at 7 time points during treatment. Apparent concentrations of oxyhemoglobin (HbO (2)), deoxyhemoglobin (Hb) and melanin were estimated by analysis of t he diffuse reflectance spectra. No changes were observed in the appare nt HbO(2) or the Hb concentration of the placebo-treated or control si tes, thus establishing a reliable baseline. The apparent HbO(2) concen tration of the tretinoin-treated sites increased significantly from ba seline to a maximum at 12-18 weeks of treatment, then returned to base line with continued applications. The changes in HbO(2) concentration agreed closely with clinical assessments of erythema. The apparent mel anin concentration, corresponding to diffuse hyperpigmentation, showed a large seasonal decrease in both the control and the treated sites, with an additional decrease in the treated sites between 12 and 18 wee ks. Erythema appeared after repeated applications and eventually resol ved under continuous treatment, The maximum decrease in hyperpigmentat ion occurred simultaneously with the maximum increase in erythema.