The majority of toxins can be found in your blood or urine. A toxicology test may be ordered by your doctor. A urine or saliva sample is used to screen for common drugs. A blood sample is needed to detect certain chemicals, such as alcohol, benzene, and mercury. Your body gets rid of waste products in the form of toxins. These toxins are removed through urine, sweat, tears, and feces (in particular, red blood cells contain hemotoxins that help destroy old or damaged blood cells). Toxic substances can also be eliminated through the lungs when we breathe out. If these routes of elimination aren't working properly, the body will retain these harmful compounds which can cause disease. There are two main types of toxins: external and internal. External toxins enter the body through the skin or via the digestive system. Common external toxins include heavy metals (such as lead, arsenic, and mercury), pesticides, and herbicides. Internal toxins are produced within the body from natural processes such as metabolism and digestion or from exposure to environmental contaminants. Examples include the production of free radicals during normal cell function or under conditions of chemical stress; inflammatory molecules such as prostaglandins and leukotrienes; and hormones like estrogen and testosterone. Hormones are responsible for many different bodily functions including growth, reproduction, and immune response.