Allergen [al-ler-jen] What it is: A substance that causes an allergic reaction in the body. This reaction can be topical or systemic. VIDEOS RELATED TO THIS TERM LEARN MORE TERMSBUFFINGBUFFERHYPONYCHIUMPLASTIC PUSHERDAPPEN DISHCALLUS SOFTENERTWO-WAY BUFFERBACKFILLBLOOMING GELACRYLICGLITTERBULLIONCUREPARONYCHIALED LAMPBUILDER GELNAIL PRIMERWATTAGEGEL SYSTEMACRYLIC BRUSH PrevNext