Toxicologists study the safety and biological effects of drugs, chemicals, agents, and other substances on living organisms. They develop methods to determine harmful effects, the dosages that cause those effects, and safe exposure limits. They may also investigate the relationship between dose and effect, which can be influenced by factors such as the dosing regimen (single large exposure vs. continuous smaller exposures), route of exposure (oral, dermal, nasal), age, gender, and environment. Toxicology brings together a wide variety of fields, including chemistry, biology, pharmacology, human and animal medicine, and environmental science, to help inform policies and regulations to protect both human health and the environment. Toxicologists spend their time planning and conducting experiments, dosing animals, and collecting and analyzing data. Ph.D. level toxicologists interpret the results of studies, conduct risk assessments, and integrate data from many different studies. They then create reports and recommendations for organizations and regulatory agencies, putting the data into context and providing risk analyses to ensure the safety of the products and compounds for their intended use.