Allergens that are the most common causes of acute and chronic allergic reactions (type I and type IV) include House dust mite feces Animal dander Pollens (tree, grass, weed) Molds Foods Insect saliva and venom (transmitted by bites and stings) Drugs Latex Household chemicals (eg, hydroxyisohexyl 3-cyclohexene carboxaldehyde, cinnamal, eugenol) For type IV hypersensitivity reactions, drugs are the most common cause.