Highlighters are minimally toxic and do not pose a serious treat to anyone's health. Most highlighters, pens and markers contain dyes, trace amounts of alcohol and a chemical known as glycol or glycol ether. Glycol can be harmful in large quantities but is not harmful in trace or small amounts.
Expected symptoms of ingesting highlighter ink include stained skin and a mildly upset stomach. If ingested, monitor the person for any unusual symptoms.
Do not use cleaning agents on the stained area, as it can be harmful to the skin's surface. The stain disappears on its own after a few days. If unusual symptoms are noticed, call the nearest poison center or consult a physician.