Toxicology is a branch of science that encompasses biology, chemistry, pharmacology , and medicine, concerned with the study of the harmful effects of chemical substances on living organisms and the practice of diagnosis and treatment when exposed to poisons and toxic substances. Factors that influence chemical toxicity include dose, duration of exposure (whether acute or chronic), route of exposure, species, age, sex, and environment. Toxicologists are experts in poisons and poisoning. There is a movement for evidence-based toxicology as part of the larger movement toward evidence-based practices. Toxicology is currently contributing to the field of cancer research because certain toxins can be used as drugs to kill tumor cells.