Toxicity is also classified according to the timing between exposure to the toxicant and the first appearance of symptoms associated with toxicity. Immediate toxicity results when the symptoms occur rapidly within seconds or minutes following exposure to the toxicant. With immediate toxicity, the relationship between causative agents or toxicants and the pathologic symptoms or toxicity is more easily established. However, some toxicants may take years to produce toxicity. This delayed toxicity adds to the difficulty in establishing the cause-and-effect relationship. For example, diethylstilbestrol (DES) is a nonsteroidal drug prescribed for women during pregnancy
to prevent miscarriage. It is now known that daughters born to mothers who took DES are at risk for developing vaginal and cervical cancers during adolescence. In this example the timing between in utero exposure to the toxicant and the first appearance of symptoms associated with toxicity may exceed 10 years.