How does radiation affect humans? Well there is many different ways it affects humans, a relatively low dose of radiation will often cause hair loss is a symptom of deeper internal cell damage with doses of between 200 and 300 or more rems. Moderate doses of radiation can cause severe damage to capillaries, and thereby damage the heart. The thyroid gland is very susceptible to radiation damage. In fact, radioactive iodine is prescribed in some cases of an overactive thyroid. The radiation in the iodine kills part of the thyroid, thus reducing its output of throid hormones. A bodys blood system has a number of functions. To bringing oxygen to cells, it is key in fighting off infetion. Doses as low as 100 rems can trigger a reduction in the bloods lymphocyte count and leave a person more prone to infection. Cases where a person has beeen exposed to a relatively low dose of radiation that causes flu like symptoms are often suffering from a drop in lymphocytes. This is often called a mild dose of radiation sickness. Symptoms can last for as long as ten years and patients experiencing mild radiation sickness are more susceptible to the cancers lymphoma and leukemia. Reproductive cells divide quickly. As such, the reproductive system is very susceptible to radiation damage. Damage can occur with a dose as low as 200 rems. Many victims of radiation poisoning become sterile. Radiation causes fundamental changes to the genetic, or DNA, structure of cells. This genetic damage sometimes results in cells growing out of control or not dying at the correct time. These cell growths form cancerous tumors. What is background radiation? Ionizing radiation that people on the planet earth are exposed to, including natural and artificial sources. Radioactive material is found throughout nature. Dectectable amounts occur naturally in soil, rocks, water, air, and vegetation, from which it is inhaled and ingested into the body. Humans can receive internal exposure, or external exposure…