Fluorescein isothiocyanate (FITC)-induced contact hypersensitivity is a mouse model of skin allergy to chemicals. In this model, chemicals such as phthalate esters are known to enhance skin sensitization to FITC. The article by Matsuoka et al. demonstrated that butyl paraben (BP), a common preservative, enhances skin sensitization as revealed by ear-swelling response to FITC. Mechanistically, BP facilitates dendritic cell trafficking from skin to lymph nodes, and enhances cytokine production from lymph node cells. Their results provide direct in vivo evidence that BP, like phthalate esters, enhances sensitization to other chemicals.