Cell cycle analysis by flow cytometry of non‐exposed, sun‐exposed, and tretinoin‐treated skin

The percentage of keratinocytes in the proliferative phase of the cell cycle (S + G₂+ M) was measured by DNA How cytometry in sun‐exposed, non‐exposed, and tretinoin‐treated skin. Before tretinoin treatment, the percentage of keratinocytes actively cycling was higher in sun‐exposed than in non‐sun‐exposed skin (p = .002) and was correlated with clinically assessed photo‐damage (p = .007). Subsequently, tretinoin‐treated sun‐exposed skin was compared to the pre‐treatment sun‐exposed skin. Overall, there was no statistically significant change. However, there was a trend toward a decrease1 in the percentage of keratinocytes in the S + G₂+ M phases immediately after four months of tretinoin us that was limited to the most severely damaged patients. This effect was no longer evident two months after discontinuing treatment. This is the first study, to our knowledge, utilizing flow cytometry to investigate the effects of tretinoin in patients with varying degress of photodamage.