Novel Research Regarding Topical Use of Diclofenac in Dermatology—Non-Clinical and Clinical Data

Diclofenac, an aryl-acetic acid derivative from the non-steroidal anti-inflammatory drug class, is the subject of multiple non-clinical and clinical studies regarding its usefulness in treating some dermatologic pathologies with an inflammatory, auto-immune, or proliferative component. Diclofenac is now approved for the topical treatment of actinic keratoses (AK), pre-malignant entities that have the risk of transformation into skin carcinomas. The hypothesis that diclofenac increases granular layer development in the mice tail model, having an anti-psoriatic effect, was demonstrated in a previous study in which 1% and 2% diclofenac ointment was evaluated. The aim of the present study was to perform experimental research on the topical effect of diclofenac in the mice tail model, by testing 4% and 8% diclofenac ointment, which is presented in the first part of the manuscript. In the second part of the manuscript, we also aimed to conduct a literature review regarding topical diclofenac uses in specific dermatological entities by evaluating the articles published in PubMed and Scopus databases during 2014–2025. The studies regarding the efficacy of topical diclofenac in dermatological diseases such as AK and field cancerization, actinic cheilitis, basal cell carcinoma, Bowen disease, Darier disease, seborrheic keratoses, and porokeratosis, were analyzed. The results of the experimental work showed a significant effect of 4% and 8% diclofenac ointment on orthokeratosis degree when compared to the negative control groups. Diclofenac in the concentration of 4% and 8% significantly increased the orthokeratosis degree compared to the negative control with untreated mice (p = 0.006 and p = 0.011, respectively, using the Kruskal–Wallis test) and to the negative control with vehicle (p = 0.006 and p = 0.011, respectively, using the Kruskal–Wallis test). The mean epidermal thickness was increased for the diclofenac groups, but not significantly when compared to the control groups. The results are concordant with our previous experiment, emphasizing the need for future clinical trials on the use of topical diclofenac in psoriasis.