Irritating, allergy-producing, neurotoxic, and carcinogenic. Can cause insomnia, coughing, headaches, nausea, nosebleeds, and skin rashes. Some of the most irritating and allergenic preservatives contain, release, or break down into formaldehyde. These include 2-bromo-2-nitropropane-1,3-diol, diazolidinyl urea, DMDM hydantoin, imidazolidinyl urea, and quaternium 15. Widely used in deodorizers, disinfectants, personal-care products (including shampoos), and cosmetics (including nail polishes and hardeners). A common air pollutant, it is also used in permanent-press sheets, mattresses, foams, plastics, and building materials.