TLR4 and skin sensitization: The minimum amount of nickel to induce skin sensitization in transgenic mice expressing human TLR4 was reduced when nickel was co‐applied with LPS, and both the sensitization and elicitation steps during nickel allergy coincided with activation of TLR2 and TLR4, suggesting a potential role of bacteria exposure as well as nickel in inducing skin sensitization.15, 35, 40, 45, 88