Isothiazolinones, preservatives including methylisothiazolinone (MI), methylchloroisothiazolinone/methylisothiazolinone (MCI/MI), benzisothiazolinone (BIT), and octylisothiazolinone (OIT), are notorious contact allergens. Pediatric dermatologists are familiar with these preservatives in personal care products, homemade slime recipes, and wet wipes. We present a novel source of MI declared in nail polish marketed to children.