Jacobaea vulgaris is a biennial or perennial herb, reaching up to 200 cm, with pinnatifid leaves and numerous yellow flowerheads borne in flat-topped corymbs. The blooming season starts in June and lasts till September. The weed prefers waysides, railway embankments, pastures, and wastelands. While considered an indigenous herb of Europe and Western Asia, it is also widely found in North and South Americas, South Africa, India, Siberia, New Zealand, and Australia, where it poses a serious threat for agriculture and local ecosystems in the absence of natural insects and pathogen species. Although the plant was utilized in Early Modern Europe as a medicine for various purposes, it contains numerous harmful ingredients. Sesquiterpene lactones (STLs) are responsible for allergic dermatitis and phototoxic properties of the sap, while pyrrolizidine alkaloids (PAs) pose a serious threat to livestock after ingestion. Jacobaea vulgaris has been regarded as a noxious weed since the 19th century. In the present day, its eradication from pastures is regulated by law in many countries. Nevertheless, migrant workers might not be conscious that this weed is dangerous. In the summer of 2012, a young migrant male farm worker was seen in the University Dermatology Out-Patient Clinic in Poznan due to acute blistering Jacobaea vulgaris-induced dermatitis clinically resembling dermatitis herpetiformis (cutaneous manifestation of gluten intolerance). The biological/chemical/mechanical control of the plant in farmlands, as well as education at an early age about poisonous and injurious herbs, is advisable for preventing potentially serious health hazards, particularly to urban dwellers accidentally exposed to those plants at their urban stands.