Reports have surfaced from Japan that dozens of residents are being treated for radiation poisoning in the aftermath of the magnitude 9 earthquake that caused damage to five of Japan’s nuclear reactors.

Reactors at the Fukushima Daiichi nuclear plant, in Onahoma City, began leaking radiation over the weekend, and thousands of people had to be evacuated from their homes. However, it appears that despite these measures, 23 people are currently being treated for radiation exposure, which can lead to acute radiation syndrome – or radiation poisoning.

Radiation poisoning can occur either when the body is suddenly exposed to high levels of toxic radiation or when it is exposed to lower levels for prolonged periods of time. Poisoning can result in substantial damage to human body tissues, premature aging, cancer and even death.

One hundred millisieverts of radiation a year is enough to cause a clear increase in the risk of cancer. Larger amounts, naturally, increase the risk even further. A dose of 1,000 millisieverts can cause radiation sickness and decrease white blood cell counts. A dose of 5,000 millisieverts kills about half of those exposed within a month.

In comparison, humans are typically exposed to about 2 millisieverts a year from radiation that occurs naturally in soil and cosmic rays. Chest X-rays emit about 0.1 millisieverts.

Early symptoms of radiation poisoning include nausea, vomiting and diarrhea, which can start within minutes to days of exposure and last for days. Following that, a person may look and appear healthy, but they will soon become sick again, suffering from loss of appetite, fatigue, fever and possibly seizures and coma. These more serious symptoms may last for hours or months.

The condition is treated with stable potassium iodide, a salt that protects the body from radiation by blocking the intake of radioactive material in the thyroid. It is most effective when it is distributed before exposure, and it can provide protection for up to 24 hours afterwards. Japan has already distributed 230,000 doses of potassium iodide to evacuation centers housing people from the areas around the damaged nuclear reactors.

On the West Coast of the United States, sales of potassium iodide have skyrocketed in the past few days due to fears that radiation may sweep across the Pacific. Pharmacies typically do not stock the product, but it has always been readily available over the Internet – until recently.

Many outlets that sell potassium iodide have been flooded with orders, which has lead to a shortage. Companies say that callers often end up in tears when told the product is unavailable, even after being reassured that the chance of radiation reaching the U.S. is actually very low.

It is worth noting that potassium iodide only protects the thyroid from exposure and not other parts of the body that radiation can affect, such as the cells lining the intestines and stomach, and in the bone marrow. Moreover, potassium iodide cannot undo damage that has already been done to the thyroid. This is why it is vital to receive treatment as quickly as possible following exposure.

Dr. Manny Alvarez serves as Fox News Channel's senior managing health editor. He also serves as chairman of the department of obstetrics/gynecology and reproductive science at Hackensack University Medical Center in New Jersey. Click here for more information on Dr. Manny's work with Hackensack University Medical Center. Visit AskDrManny.com for more.