TNF and dermatitis: TNF‐α is a key factor involved in TPA‐induced dermatitis, especially at the stage where dermal edema is significant.[22] Topical application of TPA has been shown to induce TNF‐α expression at the application site.[22a] Exposure of a mouse ear to 2.4 μg TPA (in neat DMSO) for 30 min led to a significant increase in ear thickness and tissue weight (Figure 4A).